2011

Mesoscale Discussion #0167


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 28...29...CONTINUES.

   

GREATEST THREAT FOR DAMAGING WINDS AND TORNADOES EXPECTED ACROSS THE NRN EXTENT WW 29...SPREADING FROM SRN IND INTO NRN KY.  PARTS OF WW/S 28 AND 29 WILL LIKELY NEED TO BE EXTENDED INTO NRN KY BY 0930Z...GIVEN FASTING MOVING LINE OF STORMS EXPECTED TO EXIT WW 29 BY 10Z.

   

AT 09Z...REGIONAL RADAR IMAGERY SHOWED A FAST MOVING /55-60 KT/ LINE OF STORMS EXTENDING NNE-SSW FROM WASHINGTON INTO HARRISON COUNTIES IN EXTREME SRN IND.  THIS LINE...WITH BOWING TENDENCIES AT TIMES...HAS A HISTORY OF DAMAGE ACROSS SWRN IND /REFERENCE LOCAL STORM REPORTS FROM WFO PAH FOR GIBSON COUNTY/.  AIR MASS IMMEDIATELY DOWNSTREAM OF THESE FAST MOVING STORMS REMAINS UNSEASONABLY WARM AND MOIST...WITH NO INHIBITION.  THUS...THREAT FOR DAMAGING WINDS AND TORNADOES IS EXPECTED TO PERSIST EWD INTO NRN KY EARLY THIS MORNING.

   

FARTHER SW...RADAR IMAGERY SHOWED THE GUST FRONT HAS MOVED EWD JUST AHEAD OF THE TSTMS EXTENDING INTO WRN KY...THOUGH A THREAT FOR DAMAGING WINDS WILL PERSIST IN THE SHORT TERM...GIVEN STRENGTH OF LOW LEVEL WINDS /60 KT/ PER AREA VWPS.

Mesoscale Discussion #0256


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 56...58...CONTINUES.

   

...WW 58 AND SRN EXTENT OF WW 56... --- THREAT FOR TORNADOES CONTINUES ACROSS PARTS OF MIDDLE INTO ERN TN...WITH THIS THREAT ADVANCING INTO NRN AL SUCH THAT AN AREAL EXTENSION OF WW 58 HAS OCCURRED PER RECENT SPC-WFO COORDINATION. ---

   

REGIONAL RADAR IMAGERY SHOWED A BROKEN LINE OF STORMS EXTENDING FROM SWRN VA THROUGH NERN TO SRN MIDDLE TN NEAR THE AL BORDER.  ALTHOUGH THE AIR MASS ALONG AND E TO S OF THIS LINE OF STORMS REMAINS ONLY MARGINALLY UNSTABLE...STRONG FORCING FOR ASCENT WITHIN EXIT REGION OF 100 KT WLY MIDLEVEL JET OVER TN COMBINED WITH 50-65 KT EFFECTIVE BULK SHEAR CONTINUES TO SUPPORT STORM ORGANIZATION.  IN ADDITION... LOW LEVEL SHEAR /300-500 M2/S2 OF EFFECTIVE SRH/ EXTENDING FROM NRN AL TO ERN TN TO WRN NC SUPPORTS THE CONTINUED THREAT FOR TORNADOES YET THIS EVENING.

   

...NRN EXTENT OF WW 56... WEAKER INSTABILITY WITH NWD EXTENT ACROSS WW 56...LIKELY DUE TO EARLIER CONVECTION MOVING THROUGH THIS REGION AND NOW LOCATED E OF WW 56...SUGGESTS THE OVERALL SEVERE WEATHER THREAT SHOULD CONTINUE TO WANE.  THE EXCEPTION MAY BE WITH ACTIVITY CURRENTLY LOCATED OVER FAR SWRN VA IN SCOTT COUNTY...WITH THESE PARTICULAR STORMS AFFECTING THE BORDER REGION OF SWRN VA/NERN TN/NWRN NC.

Mesoscale Discussion #0353


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 95...96...CONTINUES.

   

...INCREASING POTENTIAL FOR TORNADOES /POSSIBLY STRONG/ THROUGH MID-EVENING ACROSS CNTRL/SRN AL AND SERN MS....

   

23Z MESOANALYSIS PLACES A MESOLOW OVER ECNTRL MS WITH PERSISTENT PRESSURE FALL AXIS NEWD INTO CNTRL/NERN AL. CONSIDERABLE AMOUNT OF PRE-QLCS TSTMS HAVE ERUPTED AHEAD OF THE MESOLOW IN SERN MS...PRESUMABLY GIVEN ACCELERATION OF THE LOW-LEVEL FLOW AND INCREASING LARGE-SCALE ASCENT.  THESE MORE DISCRETE CELLS SHOULD PERSIST/ADVANCE ENE INTO CNTRL/SRN AL THROUGH THE EVENING WITH HIGHEST POTENTIAL FOR STRONG TORNADOES IN AN 80 MILE CORRIDOR CENTERED 30SSE OF PINE BELT MS-SELMA AL-25W ANNISTON AL.

   

BMX VWP SUGGESTS THE 0-1KM FLOW HAS BACKED AND ACCELERATED WITH 0-1KM SRH IN EXCESS OF 350 M2/S2 NOW.  CONCERN IS THAT AS THE DISCRETE CELLS MOVE INTO THAT AREA AND/OR INTERACT WITH THE QLCS...TORNADO POTENTIAL WILL INCREASE.  OTHERWISE...BOWS/LEWPS WITHIN THE LINE WILL POSE AN ADDED DAMAGING WIND THREAT.

Mesoscale Discussion #0392


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 116 CONTINUES.

   

WARM ADVECTION APPEARS TO BE THE PRIMARY FORCING MECHANISM FOR ONGOING ACTIVITY ACROSS THE NRN THIRD OF WW116.  SEVERAL LONG-LIVED SUPERCELLS...A FEW TORNADIC...PERSIST WITHIN THIS ENVIRONMENT AND SHOULD CONTINUE THEIR MOVEMENT NEWD AS WARM FRONT GRADUALLY RETREATS TOWARD THE MN BORDER.  IT/S NOT ENTIRELY CLEAR HOW MUCH REDEVELOPMENT WILL OCCUR LATER ACROSS NEB ALTHOUGH LATEST IR IMAGERY DOES SUGGEST STRONGER FORCING WILL BEGIN TO OVERSPREAD THE WARM/MOIST SECTOR OVER THE NEXT 2-4 HR.  GIVEN THAT THE AIRMASS REMAINS MOIST/UNSTABLE AND LLJ IS EXPECTED TO INCREASE MARKEDLY BY 06Z ACROSS ERN NEB IT APPEARS AT LEAST A LOW THREAT FOR ANOTHER BOUT OF SEVERE IS POSSIBLE.


**This MCD preceded the Pocahontas, Iowa EF3 and EF4 tornadoes

Mesoscale Discussion #0399


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 120 CONTINUES.

   

THE REMAINDER OF THE WESTERN AND CENTRAL UPPER PENINSULA OF MICHIGAN MAY NEED TO BE ADDED TO WW 120 WITHIN THE NEXT HOUR OR TWO.

   

SCATTERED VIGOROUS STORMS ARE ONGOING...FROM NEAR THE DEEP SURFACE CYCLONE CENTER MIGRATING ACROSS NORTHWEST WISCONSIN...SOUTHWARD TO THE VICINITY OF A 90 KT SOUTHWESTERLY 500 MB JET AXIS ACROSS SOUTHWEST WISCONSIN.  AN EMBEDDED SPEED MAXIMUM IS IN THE PROCESS OF NOSING ACROSS THE UPPER MISSISSIPPI VALLEY TOWARD THE UPPER GREAT LAKES REGION...WITH A REGION OF ENHANCED UPPER DIVERGENCE CONTRIBUTING TO CONVECTIVE DEVELOPMENT.  THIS ACTIVITY APPEARS LIKELY TO GENERALLY MAINTAIN ITS DISCRETE NATURE AT LEAST ANOTHER COUPLE OF HOURS AS UPPER FORCING SPREADS ACROSS NORTHEASTERN WISCONSIN AND THE WESTERN UPPER PENINSULA OF MICHIGAN THROUGH 01-02Z.  IN THE PRESENCE OF MODERATELY STRONG MIXED LAYER CAPE/1000-1500 J PER KG/ AND STRONG DEEP LAYER SHEAR...AS WELL AS PERHAPS ENLARGING LOW-LEVEL HODOGRAPHS...TORNADIC POTENTIAL COULD STILL INCREASE EARLY THIS EVENING.  LARGE HAIL WILL CONTINUE POSSIBLE...ALONG WITH LOCALLY DAMAGING WIND GUSTS.


**This MCD preceded the Merrill, Wisconsin EF3 tornado

Mesoscale Discussion #0426


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 135 CONTINUES.

   

A DRYLINE EXTENDS FROM THE KS/OK BORDER 20 NNE OF PNC TO 25 SE OF OKC TO THE RED RIVER 25 WSW OF ADM AND FARTHER S-SW INTO N-CNTRL TX. THE ARCING LINE OF SEMI-DISCRETE SUPERCELLS THAT INITIATED ALONG THE DRYLINE CONTINUES TO SHIFT EWD TOWARD ERN OK...AND WILL CONTINUE TO DO SO DURING THE NEXT FEW HOURS GIVEN EFFECTIVE BULK SHEAR VECTORS ORTHOGONAL TO THE DRYLINE WITH MAGNITUDES OF 45 TO 60 KT. THIS DEGREE OF DEEP-LAYER WIND SHEAR WILL MAINTAIN THE SUPERCELL THREAT AS STORMS APPROACH THE TULSA AND MCALESTER AREAS THROUGH 2330Z WHILE TRAVERSING MLCAPE VALUES OF 2000-2500 J/KG. EFFECTIVE SRH VALUES OF 100-200 M2/S2 SUPPORT A TORNADO THREAT ANY SUSTAINED SUPERCELLS. THIS THREAT WILL FURTHER INCREASE INTO THE EVENING...ALONG WITH THE THREAT FOR STRONG TORNADOES...AS EFFECTIVE SRH VALUES INCREASE PER THE LATEST RUC GUIDANCE. THE GREATEST THREAT FOR STRONG TORNADOES WILL BE ACROSS SERN OK INTO FAR NERN TX THROUGH 00Z...WHERE SFC-3 KM CAPE VALUES FROM 100-150 J/KG WILL PROVIDE ENHANCED LOW-LEVEL BUOYANCY TO THE RELATIVELY MORE DISCRETE CONVECTION /COMPARED TO FARTHER NORTH/.

   

FARTHER SOUTH ALONG THE DRYLINE...CONVECTION IS INITIATING ACROSS PORTIONS OF N-CNTRL TX TO THE NORTH OF THE DFW AREA. GIVEN THE DEGREE OF POTENTIAL INSTABILITY AND DEEP-LAYER WIND SHEAR...THESE STORMS COULD EVENTUALLY POSE A THREAT FOR LARGE HAIL. THERE WILL ALSO BE A THREAT FOR A TORNADO GIVEN THE VEERING WIND PROFILE EVIDENT IN THE SFC-2-KM LAYER PER THE NEARBY FORT WORTH VWP. THUS...THE TORNADO WATCH MAY NEED TO BE EXTENDED FARTHER SOUTH BY ONE TIER OF COUNTIES IN NERN TX IF STORMS FURTHER INTENSIFY.

   

LATEST RUC GUIDANCE IS SUGGESTING THAT THE DRYLINE WILL REMAIN STATIONARY INTO EARLY EVENING ACROSS CNTRL/SRN OK...AND POTENTIALLY BE NUDGED WWD A BIT. THIS MAY SERVE TO FOCUS ANOTHER ATTEMPT AT CONVECTIVE INITIATION AFTER 00Z AS AN AREA OF DEEP-LAYER ASCENT APPROACHES. THIS IS SUPPORTED BY THE LATEST EXPERIMENTAL HRRR GUIDANCE...AND THESE TRENDS WILL CONTINUE TO BE MONITORED FOR A PERSISTENT SEVERE THREAT INTO THE EVENING ACROSS THE WRN PORTIONS OF THE WATCH.

Mesoscale Discussion #0438


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 140...141...CONTINUES.

   

CONTINUE W 141.  REPLACEMENT WW FOR 140 IS LIKELY BEFORE SCHEDULED 20Z EXPIRATION...BECAUSE SVR THREAT WILL PERSIST WELL BEYOND THAT TIME AND PRIOR TO COLD FROPA.

   

18Z SFC MESOANALYSIS SHOWED COLD FRONT CONTINUING TO MOVE EWD ACROSS NERN...CENTRAL AND SWRN LA...WITH WARM FRONT ANALYZED ROUGHLY 30 NNE TCL...TCL...GZH...NSE AND LIFTING NEWD ACROSS W-CENTRAL/S-CENTRAL AL.  PRE COLD-FRONTAL CONFLUENCE LINE IS PIVOTING EWD ACROSS SWRN/CENTRAL MS WHILE DRIFTING EWD ACROSS SERN LA.  AS THESE PROCESSES CONTINUES...FAVORABLY BUOYANT AND STRONGLY HEATED AIR MASS...CHARACTERIZED BY MLCAPE 1000-2000 J/KG...WILL OVERSPREAD PROGRESSIVELY MORE OF CENTRAL/SRN AND EVENTUALLY ERN AL...THROUGH LATE AFTERNOON.  NRN FRINGE OF STRONGEST HEATING IS EVIDENT IN SFC DATA AND VIS IMAGERY ROUGHLY ALONG JAN-EET LINE...AND HAS MOVED N OF MEI.  STORMS WITHIN AND JUST N OF THAT BOUNDARY MAY ENCOUNTER ENHANCED LOW-LEVEL VORTICITY/ASCENT.  THIS INCLUDES LONG-LIVED SUPERCELL NOW MOVING TOWARD PORTIONS SUMTER/GREENE/HALE/TUSCALOOSA COUNTIES AL THAT PRODUCED DAMAGING TORNADO IN JAN AREA AROUND 16Z...AND MORE RECENTLY...REPORT OF LARGE TORNADO IN KEMPER COUNTY AT 1820Z.  UPSHEAR SUPERCELLS S AND SW JAN ALSO MAY INTERACT WITH THAT BOUNDARY.  CELLS OVER SERN MS AND SRN AL MAY ENCOUNTER WARM FRONT...WHERE LOW-LEVEL BACKING/VORTICITY/HODOGRAPHS WILL BE RELATIVELY MAXIMIZED.  BOTH REGIMES MAY SUPPORT CORRIDORS OF LOCALLY ENHANCED TORNADO POTENTIAL...WITH EFFECTIVE SRH REACHING 500 J/KG.  HOWEVER...STG LOW-MIDLEVEL SPEED SHEAR WILL SUPPORT SUPERCELL THREAT EVEN AS FAR W AS S-CENTRAL LA.

   

SVR POTENTIAL MAY EXTEND INTO PORTIONS WRN GA DURING NEXT 2-3 HOURS WITH CELLS WELL NE OF SFC WARM FRONT...BUT IN REGIME OF ELEVATED WAA AND STRENGTHENING BUOYANCY/SHEAR ALOFT...SUPPORTING OCNL HAIL.  BETTER-ORGANIZED THREAT THERE IS NOT EXPECTED UNTIL LATE AFTERNOON INTO EVENING.

Mesoscale Discussion #0444


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 141 CONTINUES.

   

NUMEROUS SUPERCELLS WILL CONTINUE TRACKING E-NEWD ACROSS WW141 INTO EARLY EVENING. THE GREATEST INSTABILITY -- MLCAPE VALUES AOA 1000 J PER KG -- IS CURRENTLY CONFINED TO W-CNTRL AND SWRN INTO S-CNTRL AL INVOF A SFC MOIST AXIS FEATURING DEWPOINTS IN THE MIDDLE TO UPPER 60S. THIS IS WHERE THE GREATEST THREAT FOR PERSISTENT/CYCLIC SUPERCELL STRUCTURES EXISTS. AS THE MOIST AXIS SHIFTS EWD IN TIME...THIS THREAT WILL CONTINUE TO EXPAND INTO CNTRL AL. VERY STRONG LOW-LEVEL WIND SHEAR IS RESULTING IN EFFECTIVE SRH VALUES AOA 500 M2/S2 AND WILL SUPPORT A CONTINUED THREAT FOR TORNADOES...SOME POTENTIALLY STRONG. WITHIN THE LOWEST FEW KM AGL...BIRMINGHAM VWP DEPICTS STRONG CLOCKWISE CURVATURE IN THE HODOGRAPH ATOP A LONG STRAIGHT-LINE HODOGRAPH. THIS SUGGESTS THAT THE GREATEST THREAT FOR STRONG TORNADOES WILL OCCUR WITH ANY RIGHT-MOVING /EASTWARD-MOVING/ SUPERCELLS ACROSS CNTRL AL.

   

FARTHER NORTH...EARLIER WIDESPREAD CONVECTION HAS RESULTED IN A COLD POOL ACROSS NRN AL INDUCING A STATIONARY BOUNDARY DRAPED ACROSS THE NRN PART OF THE STATE /FROM 25 SW RMG TO 20 NNE BHM TO 35 SSW MSL/. ENHANCED VORTICITY NEAR THIS BOUNDARY COULD ALSO FOCUS AN ENHANCED AREA OF TORNADO POTENTIAL ALONG AND JUST SOUTH OF THE BOUNDARY DURING THE NEXT COUPLE OF HOURS. HOWEVER...MORE NUMEROUS CONVECTION IN THIS AREA COMPARED TO THE SOUTH COULD YIELD MORE FREQUENT CELL INTERFERENCE AND MITIGATE A MORE SIGNIFICANT TORNADO POTENTIAL.

   

THE THREAT FOR SEVERE THUNDERSTORMS AND TORNADOES WILL PERSIST WELL PAST THE EXPIRATION TIME OF 02Z. THUS...A NEW TORNADO WATCH WILL BE NEEDED PRIOR TO 02Z ACROSS MUCH OF THE ONGOING TORNADO WATCH 141 AND DOWNSTREAM INTO SERN AL AND THE WRN FL PANHANDLE.

Mesoscale Discussion #0450


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 147 CONTINUES.

   

A NEW WW LIKELY WILL BE ISSUED BY 10Z EXPIRATION OF WW 147.

   

IN RESPONSE TO ONGOING SURFACE PRESSURE FALLS TO THE LEE OF THE SOUTHERN APPALACHIANS...OBSERVATIONAL AND MODEL DATA INDICATE A LOW-LEVEL MOISTURE RETURN OFF THE SOUTH ATLANTIC COAST THROUGH THE SAVANNAH VALLEY AND CAROLINA COASTAL PLAIN THIS MORNING.  ALTHOUGH LAPSE RATES ARE GENERALLY WEAK...THIS MAY CONTRIBUTE TO SUFFICIENT DESTABILIZATION FOR INCREASING CONVECTIVE DEVELOPMENT ACROSS NORTH CENTRAL/NORTHEAST GEORGIA INTO THE WESTERN NORTH CAROLINA THROUGH DAYBREAK.  ALTHOUGH A MORE SUBSTANTIVE INCREASE IN SEVERE POTENTIAL ACROSS THE CAROLINAS MAY NOT OCCUR UNTIL MID TO LATE MORNING WITH BOUNDARY LAYER HEATING...BOUNDARY LAYER BASED STORMS MAY BECOME INCREASINGLY LIKELY EAST OF ATHENS GA INTO WESTERN SOUTH CAROLINA BY 11-13Z.  STRENGTHENING LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION ASSOCIATED WITH AN APPROACHING SHORT WAVE IMPULSE WILL CONTRIBUTE TO THIS POTENTIAL...AND...IF IT OCCURS...STRONG DEEP LAYER SHEAR AND LARGE CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS WILL BE FAVORABLE FOR SUPERCELLS CAPABLE OF PRODUCING TORNADOES.

Mesoscale Discussion #0454


CONCERNING...OUTLOOK UPGRADE 

   

VALID 161616Z - 161715Z

   

AN UPGRADE TO HIGH RISK FOR THE 1630Z CONVECTIVE OUTLOOK UPDATE IS FORTHCOMING FOR ERN NC.  THE COMBINATION OF VERY STRONG SHEAR/MODERATE INSTABILITY...INCREASING LOW LEVEL MOISTURE...AND LARGE SCALE ASCENT ACROSS THE REGION THIS AFTERNOON/EVENING LENDS CONFIDENCE IN THE FORECAST FOR AN OUTBREAK OF SEVERE STORMS CAPABLE OF PRODUCING SIGNIFICANT TORNADOES.

Mesoscale Discussion #0460


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 150 CONTINUES.

   

BKN BAND OF SVR CONVECTION...INCLUDING A FEW CYCLIC/LONG-TRACKED SUPERCELLS WITH HISTORY OF DESTRUCTIVE TORNADOES...IS MOVING NEWD ACROSS WW IN SRN VA AND CENTRAL-ERN NC.  CONDITIONS REMAIN QUITE FAVORABLE FOR TORNADIC SUPERCELLS TO PERSIST EWD ACROSS COASTAL PLAIN TO TIDEWATER...CONTINUING ONGOING REGIME OF DAMAGING/SIGNIFICANT TORNADO POTENTIAL FOR A FEW MORE HOURS AT LEAST.

   

SFC ANALYSIS INDICATES WARM FRONT LIFTING NWD ACROSS CENTRAL AND SERN VA...WHICH WILL LEAVE ENTIRE WW IN SFC-BASED EFFECTIVE INFLOW SHORTLY.  STG PRESSURE FALLS CONTINUE AHEAD OF PRIMARY TSTM CORRIDOR...ARE HELPING TO MAINTAIN RELATIVELY BACKED SFC WINDS...ENLARGED LOW-LEVEL HODOGRAPHS AND FAVORABLE STORM-RELATIVE INFLOW.  ALTHOUGH RDU VWP HAS BEEN AFFECTED BY GUST FRONT FROM EARLIER TORNADIC SUPERCELL IN THAT AREA...PRE-STORM PROFILE...INTERPOLATED WITH VWP AT AKQ...APPEAR TO REPRESENT KINEMATIC ENVIRONMENT WELL OVER NERN NC AND SERN VA.  THOSE DATA...ALONG WITH MODIFIED RUC SOUNDINGS...INDICATE 0-1 KM SRH AROUND 500 J/KG...TRENDING TO AROUND 250-300 J/KG OVER EXTREME ERN SC...WITH 0-3 KM SRH UP TO 900 J/KG AND 0-1 KM SHEAR MAGNITUDES 35-40 KT IN SERN VA NEAR WARM FRONT.  SUCH LOW-LEVEL SHEAR AND SRH ARE EXTREME FOR ANY AIR MASS WITH SFC-BASED PARCELS...AND ARE SUPERIMPOSED ON 50-60 KT EFFECTIVE SHEAR MAGNITUDES.  MLCAPE WILL RANGE FROM AROUND 500 J/KG OVER SERN VA TO NEAR 1500 J/KG OVER SERN NC AND ERN SC THROUGH 23Z.

Mesoscale Discussion #0462


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 150 CONTINUES.

   

THREAT FOR TORNADOES...LARGE HAIL AND DAMAGING WIND CONTINUES FROM COASTAL SC...ERN NC INTO SERN VA. THE THREAT FOR STRONG TORNADOES APPEARS GREATEST FROM ERN NC THROUGH SERN VA NEXT FEW HOURS. CURRENT INDICATIONS ARE THAT SEVERE THREAT MAY PERSIST OVER EXTREME ERN NC ABOUT 1-2 HOUR BEYOND EXPIRATION TIME OF TORNADO WATCH 150. A LOCAL EXTENSION IN TIME MAY BE NEEDED PRIOR TO WW EXPIRATION FOR A PORTION OF MOREHEAD CITY AND MAYBE WAKEFIELD CWA.

   

LINE OF DISCRETE SUPERCELLS CONTINUES THROUGH INSTABILITY AXIS WITH 500-1000 J/KG MLCAPE FROM COASTAL SC...ERN NC INTO SERN VA. STORMS ARE MOVING WITH AN EWD COMPONENT OF 30 KT WHICH SUGGEST THEY WILL NOT CLEAR THE NC OUTER BANKS UNTIL AROUND 02-03Z. GIVEN THE DISCRETE STORM MODE...VERY LARGE HODOGRAPHS WITH 0-1 KM SRH FROM 500-700 M2/S2...AND MODEST BUT SUFFICIENT SBCAPE...THREAT FOR STRONG TORNADOES WILL PERSIST NEXT FEW HOURS OR UNTIL ACTIVITY CLEARS THE COAST. BACK EDGE OF SEVERE THREAT AND REDEVELOPMENT APPEARS TO BE WITH BAND OF STORMS DEVELOPING FROM NEAR BRUNSWICK NC NWD TO JUST WEST OF WAKEFIELD VA.

Mesoscale Discussion #0475


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 154 CONTINUES.

   

LATEST SURFACE ANALYSIS PLACES LOW PRESSURE 45 NNW STL WITH A WARM FRONT EXTENDING EWD FROM THE LOW TO NEAR SPI AND THEN EWD INTO WRN IND 30 ENE HUF. A COLD FRONT EXTENDS S-SWD FROM THE LOW TO 10 NNW TBN TO 15 SSE OF UMN. THE MOST VIGOROUS AND WIDESPREAD CONVECTIVE DEVELOPMENT /INCLUDING DISCRETE AND SEMI-DISCRETE SUPERCELLS/ OVER THE PAST HOUR HAS BEEN NOTED IN THE ERN SEMICIRCLE OF THE LOW WITHIN 60 NM OF THE LOW CENTER. BACKED SFC FLOW IN THIS REGION...ESPECIALLY INVOF THE WARM FRONT...IS SUPPORTING STRONG LOW-LEVEL VERTICAL WIND SHEAR AND EFFECTIVE SRH VALUES OF 300-400 M2/S2. THE SFC LOW IS FORECAST TO SHIFT E-NEWD INTO CNTRL IL DURING THE NEXT COUPLE OF HOURS...WHERE PRESSURE FALLS AROUND 2 MB PER 2 HRS HAVE BEEN NOTED. CORRESPONDINGLY...THE GREATEST THREAT FOR SUPERCELLS WITH DMGG WINDS AND VERY LARGE HAIL /SUPPORTED BY MLCAPE VALUES AOA 2000 J PER KG AND STRONG CLOUD-BEARING WIND SHEAR/ WILL OCCUR WITHIN A 60-NM-WIDE AREA CENTERED ALONG A LINE FROM 45 WSW STL TO 5 ESE DEC THROUGH 00Z. THIS INCLUDES THE ST LOUIS METRO AREA /ESPECIALLY NRN SECTIONS/ BETWEEN 23Z AND 00Z. TORNADOES WILL REMAIN A CONCERN...AS WELL...ESPECIALLY WITH ANY SUPERCELLS THAT CAN REMAIN DISCRETE AND MOVE EWD NEAR THE WARM FRONT. 

   

FARTHER SOUTH ALONG THE COLD FRONT...THE PRESENCE OF SOME CINH HAS RESULTED IN FAIRLY MORE ISOLATED COVERAGE OF STORMS...EXCEPT IN S-CNTRL MO WHERE MID-LEVEL ASCENT IS MORE PRONOUNCED. THIS ACTIVITY WILL MOVE NEWD AROUND 35-40 KT WHILE TRAVERSING STRONG INSTABILITY AND EFFECTIVE BULK SHEAR MAGNITUDES AOA 45 KT...WITH BOTH LINEAR AND DISCRETE SUPERCELL MODES FAVORED. DMGG WINDS...VERY LARGE HAIL...AND TORNADOES WILL REMAIN THREATS WITH EFFECTIVE SRH VALUES OF 200-300 M2/S2.

Mesoscale Discussion #0515


CONCERNING...OUTLOOK UPGRADE 

   

VALID 221544Z - 221645Z

   

METEOROLOGICAL DETAILS FORTHCOMING IN UPCOMING 1630Z OUTLOOK

Mesoscale Discussion #0520


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 179 CONTINUES.

   

CONDITIONS REMAIN FAVORABLE FOR TORNADOES ACROSS TORNADO WATCH 179...ESPECIALLY OVER CNTRL AND ERN PORTIONS FROM THE COLUMBIA/JEFFERSON CITY/VICHY AREA EWD TOWARDS ST. LOUIS.

   

THE CNW PROFILER AND SGF VWP SHOWS RELATIVELY VEERED FLOW IN THE LOW LEVELS ACROSS WRN MO...WHICH IS RESULTING IN STRAIGHT LINE HODOGRAPHS. HOWEVER..FARTHER NE WHERE SURFACE WINDS ARE MORE BACKED AHEAD OF THE LOW AND IN THE WAKE OF EARLIER CONVECTION...SHEAR IS STRONGER WITH 0-1 KM SRH OVER 300 M2/S2. SUPERCELLS JUST S OF THE COLUMBIA MO AREA HAVE SHOWN STRONG ROTATION...AND THIS TREND IS EXPECTED TO CONTINUE AS THESE CELLS ENCOUNTER GREATER LOW LEVEL SHEAR TO THE E. ISOLATED STRONG TORNADOES MAY OCCUR. 


LARGE HAIL...SOME VERY LARGE...WILL REMAIN POSSIBLE AREA-WIDE.

Mesoscale Discussion #0571


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 201 CONTINUES.

   

TORNADO WATCH 201 CONTINUES UNTIL 23Z...WITH A RISK OF TORNADOES/LARGE HAIL AND DAMAGING WINDS.

   

A NUMBER OF STRONG/SEVERE TSTMS...WITH A COMPLEX CONVECTIVE MODE...CONTINUE TO OCCUR WITHIN A CORRIDOR OF PRE-FRONTAL CONFLUENCE FROM NORTHEAST TX INTO SOUTHEAST OK/FAR WESTERN AR...WITH OTHER MORE RECENT/SEPARATE DEVELOPMENT BEGINNING TO OCCUR FARTHER WEST NEAR THE MERGING COLD FRONT/DRYLINE FORM SOUTH-CENTRAL OK INTO NORTH-CENTRAL TX. IN THE WESTERNMOST PORTIONS OF TORNADO WATCH 201...VISIBLE SATELLITE/SURFACE OBSERVATIONS REFLECT A NARROW CORRIDOR OF STRONGER IMPLIED SURFACE BASED DESTABILIZATION READILY OCCURRING ALONG/IMMEDIATELY AHEAD OF AND NEAR THE MERGING SOUTHEAST MOVING COLD FRONT/EASTWARD ADVANCING DRYLINE. HERE...MODIFICATIONS OF THE 12Z DALLAS-FORT WORTH OBSERVED RAOB ARE NOW SUGGESTIVE OF 3500+ J/KG OF WEAKLY CAPPED MLCAPE AMID UPPER 60S F SURFACE DEWPOINTS. WITH AN INITIALLY MORE ISOLATED/SEMI-DISCRETE INITIATION EXPECTED...THESE STORMS MAY PROVIDE THE MOST CONSEQUENTIAL TORNADO/VERY LARGE HAIL THREAT THROUGH THE AFTERNOON ACROSS WW 201. 

   

THAT SAID...ANY STORMS...AHEAD OF THE ENE-ADVANCING OK SURFACE LOW AND ALONG/SOUTH OF THE WEST-EAST CONVECTIVELY REINFORCED BOUNDARY FROM EAST-CENTRAL OK INTO CENTRAL AR...AND POINTS WEST-SOUTHWARD INTO THE WARM SECTOR...MAY POSE A TORNADO THREAT WITH A RELATIVELY RICH SRH ENVIRONMENT PER REGIONAL WSR-88D VWPS/PROFILERS.

   

WITH NORTH EXTENT...SURFACE BASED DESTABILIZATION REMAINS MORE UNCERTAIN ACROSS NORTHEAST OK/NORTHERN AR OWING TO CONSIDERABLE ONGOING CONVECTION...ALTHOUGH THESE AREAS WILL BE MONITORED FOR BOUNDARY LAYER RECOVERY/DESTABILIZATION THROUGH THE AFTERNOON. IN SPITE OF THE EXTENSIVE ONGOING CONVECTION...AT LEAST SOME NORTHWARD ADVANCEMENT OF THE AFOREMENTIONED WEST-EAST BOUNDARY SEEMS PROBABLE AHEAD OF THE SURFACE LOW THIS AFTERNOON/EARLY EVENING.

Mesoscale Discussion #0574

   

CONCERNING...SEVERE POTENTIAL...WATCH NEEDED SOON 

   

VALID 252008Z - 252045Z

   

AN ADDITIONAL TORNADO WATCH WILL BE ISSUED SOON FOR NORTHERN/CENTRAL PORTIONS OF AR AND NORTHERN LA.

   

THE AIRMASS CONTINUES TO DESTABILIZE ALONG/SOUTH OF A MODIFYING WEST-EAST OUTFLOW BOUNDARY ACROSS AR AMID A REGIONAL OF STRONG SURFACE PRESSURE FALLS...WITH ADDITIONAL DESTABILIZATION /ALBEIT MODEST/ EXPECTED INTO NORTHERN AR AS THE AFOREMENTIONED BOUNDARY MIXES/SHIFTS NORTHWARD AS AN EFFECTIVE WARM FRONT. AS SAMPLED BY THE 18Z LITTLE ROCK OBSERVED RAOB...STRONG SHEAR WILL CONTINUE TO SUPPORT A THREAT FOR TORNADOES /PERHAPS SOME STRONG/...IN ADDITION TO SEVERE HAIL/DAMAGING WINDS.

Mesoscale Discussion #0575


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 252134Z - 252230Z

   

ANOTHER WW IS LIKELY ACROSS MS VALLEY REGION E AND NE OF WW 205.

   

SVR TSTMS OVER NERN PORTIONS AR IN WW 205 MAY BE MAINTAINED AS THEY MOVE NEWD INTO DESTABILIZING AIR MASS OVER THIS REGION.  MAIN UNCERTAINTY INVOLVES NRN EXTENT OF FAVORABLE/SFC-BASED EFFECTIVE INFLOW...GIVEN ROBUST STRENGTH OF COLD POOL OVER MO OZARKS AND LIMITED TIME FOR DESTABILIZATION TO ITS E.  SFC MESOANALYSIS SHOWED SRN EDGE OF THAT COLD POOL FROM NEAR FLP NEWD ACROSS CARTER COUNTY MO THEN NWD TOWARD SWRN FRINGES STL AREA...E OF WHICH 3-4 MB/2-HOUR FALLS ARE FOCUSED ACROSS SERN MO/NERN AR REGION.  THIS TENDENCY IS CONSISTENT WITH SFC LOW SHIFT/DEVELOPMENT NEWD INTO REGION...WHILE RELATED ISALLOBARIC FORCING WILL MAINTAIN BACKED NEAR-SFC WINDS AND ENLARGED LOW-LEVEL HODOGRAPHS FAVORABLE FOR SUPERCELLS/TORNADO POTENTIAL.  DEEP-LAYER SHEAR WILL REMAIN SUITABLE ALSO...WITH EFFECTIVE SHEAR MAGNITUDES AROUND 45-55 KT.  OUTFLOW BOUNDARY...N OF WHICH HODOGRAPHS ARE FURTHER ENLARGED...WAS ANALYZED FROM WRN KY MCS SWWD ACROSS MEM AREA THEN NWWD OVER NERN AR.  HOWEVER...SFC DIABATIC HEATING IS DESTABILIZING AIR MASS TO ITS N SUCH THAT 500-1500 MLCAPE MAY DEVELOP ACROSS SERN MO INTO SRN IL AND WRN KY BEFORE SUNSET. WAA WILL MAINTAIN FAVORABLE BUOYANCY IN PRE-STORM ENVIRONMENT.

Mesoscale Discussion #0580


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 205...206...CONTINUES.

   

THREAT FOR SIGNIFICANT TORNADOES AND DAMAGING WIND CONTINUES ACROSS WWS ALONG AND E OF PRIMARY CONVECTIVE COMPLEX THAT EXTENDS FROM NEAR CGI THROUGH LIT-TXK CORRIDOR AND JUST N TYR AS OF 00Z.  ENVIRONMENT WILL BECOME MORE FAVORABLE OVER AR/LA BORDER REGION EWD TO DELTA REGION...FROM WRN TN SWD TO NEAR LA BORDER THROUGH REMAINDER EVENING.

   

AS OF 00Z...TORNADIC SUPERCELLS WITH HISTORY OF DAMAGE OVER HOT SPRINGS AREA...INCLUDING APPARENT DEBRIS SIGNATURE OVER SRN CONWAY COUNTY...ARE PROCEEDING NEWD ACROSS CENTRAL AR...FOLLOWED BY INCREASINGLY WELL-ORGANIZED BOW ECHO MOVING NEWD ABOUT 60 KT TOWARD LIT METRO AND CAPABLE OF SIGNIFICANT-SVR WIND.  SUPERCELLS WILL BE MOVING NEWD ABOUT 40 KT...REMAINING AHEAD OF BOW FOR ANOTHER 1-2 HOURS.  ALL THIS ACTIVITY WILL REMAIN WITHIN BAROCLINIC GRADIENT FROM CENTRAL-NERN AR AND WILL REMAIN CAPABLE OF SIGNIFICANT TORNADOES...WITH PROXIMITY 00Z LZK RAOB SHOWING 0-1 KM SRH APCHG 400 J/KG.  BLEND OF SUPERCELL AND BOW MODES IS POSSIBLE FARTHER S IN CONVECTIVE COMPLEX...AS ACTIVITY MOVES FROM NE TX AND SWRN AR ACROSS REMAINDER OF ARKLATEX REGION AND OVER SRN AR AND EXTREME NRN LA.  SERN MO/SRN IL ACTIVITY WILL MOVE INTO PROGRESSIVELY MORE STABLE AIR...BUT REMAINS CAPABLE OD DAMAGING WIND.

   

STRONG PRESSURE FALLS ARE ANALYZED OVER SERN AR...MAINTAINING BACKED SFC WINDS WITH 300-500 J/KG OF 0-1 KM SRH.  AS LLJ STRENGTHENS DURING NEXT 2-3 HOURS...LOW-LEVEL HODOGRAPHS SHOULD ENLARGE FURTHER ACROSS SRN AR...NRN LA EWD TOWARD NWRN MS AND WRN TN. RELATED WAA AND MOISTURE TRANSPORT MAY DISPERSE RELATIVE DRY POCKETS NOW ANALYZED AT SFC OVER PORTIONS NRN LA AND WRN MS...LEADING TO MORE UNIFORM FIELD OF MLCAPE RANGING FROM 500 J/KG OVER ERN AR TO 2000 J/KG IN NRN LA...AMIDST 60-70 KT EFFECTIVE SHEAR MAGNITUDES.

Mesoscale Discussion #0585


CONCERNING...OUTLOOK UPGRADE 

   

VALID 261551Z - 261645Z

   

THE EXISTING CATEGORICAL HIGH RISK WILL LIKELY BE EXPANDED NORTHEASTWARD IN THE FORTHCOMING 1630Z DAY 1 OUTLOOK TO INCLUDE REMAINING PORTIONS OF EASTERN AR...WHILE ADDING PARTS OF SOUTHWEST TN/NORTHWEST MS INTO A HIGH RISK. FOR ADDITIONAL METEOROLOGICAL DISCUSSION...SEE THE FORTHCOMING DAY 1 OUTLOOK THAT WILL BE ISSUED BY AROUND 1630Z.

Mesoscale Discussion #0589


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 261811Z - 262015Z

   

THE SEVERE THREAT IS EXPECTED TO STEADILY INCREASE THROUGH MID/LATE AFTERNOON...INITIALLY ACROSS PORTIONS OF NORTHEAST TX AND INTO SOUTHEAST OK/NORTHERN LA/SOUTHERN AR. A RELATIVELY LONG LEAD TIME/DURATION PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCH WILL LIKELY BE ISSUED BY MID AFTERNOON.

   

WITH SURFACE CYCLOGENESIS UNDERWAY ACROSS THE SOUTHERN HIGH PLAINS...THE WARM SECTOR AIRMASS...EAST OF A NEAR I-35 CENTRAL TX DRYLINE...AND ALONG/SOUTH OF A SLOW NORTHWARD-RETURNING SOUTHWEST-NORTHEAST ORIENTED FRONTAL BOUNDARY FROM THE SOUTH DFW METRO INTO SOUTHERN AR...HAS ALREADY BECOME MODERATE TO STRONGLY UNSTABLE IN THE PRESENCE OF LITTLE CINH. AFTER A BRIEF BOUT OF SHORTWAVE RIDGING AT MIDDAY...THE LEADING EDGE OF AN UPPER JET STREAK APPEARS TO HAVE REACHED THE SOUTHERN HIGH PLAINS...WITH LIKELY-ASSOCIATED DEEP MIXED CUMULIFORM DEVELOPMENT NOW EVIDENT ACROSS EASTERN NM/NORTHWEST TX PER VISIBLE SATELLITE IMAGERY. INCREASING DEEP LAYER WIND FIELD ATOP THE MOIST/UNSTABLE WARM SECTOR WILL BE HIGHLY FAVORABLE FOR SUPERCELLS WITH AN INCREASING LARGE HAIL/TORNADO THREAT INTO THIS EVENING. STRENGTHENING LOWER TROPOSPHERIC WINDS THIS EVENING WILL ACCENTUATE THE RISK OF STRONG TORNADOES ESPECIALLY ACROSS THE ARKLATEX VICINITY/ADJACENT FAR SOUTHEAST OK.

Mesoscale Discussion #0597


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 215 CONTINUES.

   

PARTICULARLY DANGEROUS /PDS/ TORNADO WATCH 215 CONTINUES UNTIL 03Z FOR PORTIONS OF NORTH-CENTRAL/NORTHEAST TX AND FAR SOUTHEAST OK TO CENTRAL/SOUTHERN AR AND NORTHERN LA. LARGE HAIL AND TORNADOES WILL REMAIN A CONCERN...WITH THE TORNADO THREAT /INCLUDING THE POSSIBILITY OF STRONG TORNADOES/ EXPECTED TO STEADILY INCREASE TOWARD/AFTER DARK.

   

SCATTERED STRONG/SEVERE TSTMS INCLUDING SUPERCELLS CONTINUE TO DEVELOP FROM THE SOUTH SIDE OF THE DFW METRO NORTHEAST INTO SOUTHERN AR. THE RELATIVELY VOLATILE WARM/MOIST SECTOR MAY CONTINUE TO RETURN NORTHWARD A DEGREE ACROSS NORTH-CENTRAL TX/TOWARD THE RED RIVER IN RESPONSE TO UPSTREAM HEIGHT FALLS/LARGE SCALE FORCING...WITH THE ARRIVAL OF MORE APPRECIABLE DEEP ASCENT /CURRENTLY ACROSS NORTHWEST TX/ LIKELY TO CONTRIBUTE TO AN UPSWING IN VIGOROUS DEEP CONVECTION BY THIS EVENING. WITH RIGHT MOVING SUPERCELL MOTIONS LARGELY PARALLEL TO THE SOUTHWEST-NORTHEAST ORIENTED FRONTAL BOUNDARY...THE MOST CONCENTRATED SEVERE/TORNADO THREAT SHOULD REMAIN FROM NEAR THE DFW METRO INTO SOUTHERN AR...LARGELY PARALLEL TO/SOUTHEAST OF I-30. THE THREAT FOR STRONG TORNADOES IS EXPECTED TO STEADILY INCREASE INTO THIS EVENING...ACCENTUATED BY AN INCREASINGLY STRONG LOW LEVEL JET WITH A CONSEQUENTIAL INCREASE IN LOW LEVEL HODOGRAPH CURVATURE/LENGTH.

Mesoscale Discussion #0601


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 215...217...221...CONTINUES.

   

SVR CONVECTION...INCLUDING SEVERAL POTENTIALLY TORNADIC SUPERCELLS...CONTINUES TO INCREASE IN COVERAGE ACROSS DISCUSSION AREA FROM ERN OK TO MS RIVER NEAR MEM.  

   

WARM-SECTOR ENVIRONMENT WILL REMAIN FAVORABLE FOR TORNADIC SUPERCELLS.  IN FACT...PRE-STORM LOW-LEVEL SHEAR PROFILES ARE EXPECTED TO BECOME VERY FAVORABLE FOR BOTH SIGNIFICANT/DESTRUCTIVE TORNADOES AND WIND DAMAGE DURING NEXT 3-4 HOURS AS LLJ STRENGTHENS JUST ABOVE SFC...SUBSTANTIALLY BOOSTING LOW-LEVEL SHEAR AND SRH.  LARGE/DESTRUCTIVE HAIL ALSO IS LIKELY FROM INDIVIDUAL SUPERCELLS.

   

SFC MESOANALYSIS SHOWS LOW OVER ERN OK JUST W FSM...COLD FRONT SWWD ACROSS LAMAR COUNTY TX...QUASISTATIONARY FRONTAL ZONE CURVING NEWD OVER NWRN AND EXTREME N-CENTRAL AR.  FRONT BECOMES COLD FRONT AGAIN FROM NERN AR NEWD ACROSS SERN MO.  THOSE FRONTAL ZONES WILL ACT AS NRN/WRN BOUNDS FOR SFC-BASED EFFECTIVE INFLOW PARCELS...ALTHOUGH TSTMS TO THEIR N AND W ACROSS SERN KS/NERN OK/SWRN MO REGION WILL BE IN FAVORABLE ELEVATED SHEAR AND BUOYANCY FOR LARGE HAIL. IN REGIME OF STG LOW-LEVEL WAA AND SHEAR SE OF FRONTAL ZONE...OUTFLOW BOUNDARIES PRODUCED BY ONGOING CONVECTION OVER AR MAY MIX/ADVECT AWAY RATHER QUICKLY...BUT ALSO CAN SUPPLY ADDITIONAL LOW-LEVEL VORTICITY/SHEAR ABOVE ALREADY STRONG ENVIRONMENTAL VALUES.  MODIFIED RAOBS AND RUC SOUNDINGS INDICATE MLCAPE RANGING FROM 3000 J/KG OVER CONVECTIVELY UNPERTURBED AIR MASS OF CENTRAL/SRN AR...NARROWING TO CORRIDOR OF 1500-2500 J/KG MLCAPE NEWD TOWARD LOWEST OH VALLEY. EFFECTIVE SHEAR MAGNITUDES 50-60 KT AND 0-1 KM SRH 150-300 J/KG ARE COMMON...WITH SRH FCST TO INCREASE SUBSTANTIALLY AFTER 00Z BENEATH LLJ.

Mesoscale Discussion #0620


A LONG LEAD-TIME/LONG DURATION PARTICULARLY DANGEROUS /PDS/ TORNADO WATCH WILL LIKELY BE ISSUED SOON...MOST CERTAIN ACROSS NORTHERN/CENTRAL PORTIONS OF MS.

   

VISIBLE SATELLITE/SURFACE OBSERVATIONAL TRENDS IMPLY RELATIVELY QUICK AIRMASS RECOVERY/DESTABILIZATION IS OCCURRING FROM LA INTO MS/AL THROUGH MID/LATE MORNING. THIS IS THE CASE NOT ONLY FOR IN THE VICINITY OF EARLY MORNING WEST-EAST OUTFLOW ACROSS MS/AL...WHERE SURFACE TEMPERATURES/DEWPOINTS HAVE EACH INCREASED 8-12F OVER THE PAST 2 HR...BUT ALSO IN THE WAKE OF AN APPARENT WAVE-LIKE FEATURE SPREADING EASTWARD CROSS CENTRAL PORTIONS OF MS/LA AS A CU FIELD OTHERWISE CONTINUES TO INCREASE/MATURE ACROSS NORTHEAST LA.

   

AIDED BY STRONG AMPLIFICATION/INTENSIFICATION OF AN INCREASINGLY NEGATIVE TILT SHORTWAVE TROUGH/ASSOCIATED JET STREAK LATER TODAY...A VOLATILE SCENARIO IS EXPECTED TO UNFOLD THROUGH THE AFTERNOON. CONVECTIVE INITIATION OF VIGOROUS CONVECTION BY EARLY/MID AFTERNOON IS WELL SUPPORTED BY EXPERIMENTAL GUIDANCE SUCH AS SEVERAL RECENT HRRR RUNS AND THE 12Z WRF-NMM. SHORT TERM FORECAST SOUNDINGS FROM GUIDANCE SUCH AS THE RUC/12Z NAM...ACCENTUATED BY VERY LONG/STRONGLY CURVED LOW LEVEL HODOGRAPHS...SUPPORT THE NOTION OF SUPERCELLS CAPABLE OF STRONG/POTENTIALLY VIOLENT TORNADOES THIS AFTERNOON/EARLY EVENING ESPECIALLY ACROSS THE HIGH RISK AREA.

Mesoscale Discussion #0626


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 271805Z - 271930Z

   

A LONG DURATION PARTICULARLY DANGEROUS /PDS/ TORNADO WATCH WILL BE ISSUED BY MID AFTERNOON FOR MUCH OF AL INTO MIDDLE TN/NORTHWEST GA...WITH AN ISSUANCE PROBABLE BY AROUND 19Z.

   

AMID CLOUD BREAKS...THE AIRMASS CONTINUES TO QUICKLY DESTABILIZE IN THE WAKE OF A DECAYING MORNING WEST-EAST BOUNDARY ACROSS AL...AND TO THE SOUTH OF A MORE RECENT MCS-INDUCED BOUNDARY/COLD POOL ACROSS FAR NORTHERN AL. WITH A CLASSIC/SYNOPTICALLY EVIDENT OUTBREAK SETUP VIA A SHORTWAVE TROUGH/STRONG JET STREAK CURRENTLY NEARING THE LOWER-MIDDLE MS RIVER VALLEY PER SATELLITE IMAGERY...AN INCREASINGLY VOLATILE SETUP IS LIKELY THROUGH THE AFTERNOON. SUPERCELLS CAPABLE OF STRONG/VIOLENT TORNADOES ARE EXPECTED TO BECOME PREVALENT ACROSS AN INCREASINGLY UNSTABLE/WEAKLY CAPPED WARM SECTOR...WITH WSR-88D VWP OBSERVED AND RUC FORECASTS REFLECTING INCREASINGLY LONG/LOOPING LOW LEVEL HODOGRAPHS. IN THE WAKE OF A MORNING SEVERE MCS...THE AIRMASS IS EXPECTED TO RAPIDLY RECOVER ACROSS FAR NORTHERN AL INTO MIDDLE TN BY LATE AFTERNOON/EARLY EVENING.

Mesoscale Discussion #0629


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 232...235...CONTINUES.

   

PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCHES 232/235 CONTINUE UNTIL 00Z/03Z RESPECTIVELY. THIS INCLUDES THE POTENTIAL FOR LONG-TRACK STRONG/PERHAPS VIOLENT TORNADOES INTO THIS EVENING AS A SEVERE WEATHER OUTBREAK ONLY INCREASES IN MAGNITUDE/RISK.

   

AN EXTREMELY DANGEROUS/LIFE-THREATENING SITUATION CONTINUES TO UNFOLD THIS AFTERNOON ACROSS A LARGE PART OF MS/AL...WITH ADJACENT PORTIONS OF TN/NORTHWEST GA ALSO EXPECTED TO BECOME A CONCERN LATE THIS AFTERNOON/EVENING. CURRENT OBSERVATIONAL TRENDS...REASONABLY SUPPORTED BY EXPERIMENTAL HRRR GUIDANCE...IMPLY THAT SCATTERED SUPERCELLS WILL CONTINUE TO FORM IN BROKEN NNE-SSW ORIENTED CORRIDORS OF SUBTLE CONFLUENCE AHEAD /EAST/ OF MORE STORMS/SUPERCELLS THAT ARE DEVELOPING ALONG A PRE-COLD FRONTAL TROUGH/DRYLINE GENERALLY NEARING I-55 IN MS. 

   

THE WARM SECTOR AIRMASS HAS AGGRESSIVELY DESTABILIZED THIS AFTERNOON AMID NEAR 70F/LOWER 70S F SURFACE DEWPOINTS...REFERENCE SPECIAL 18Z OBSERVED RAOBS FROM JACKSON MS/BIRMINGHAM AL...WITH A WIDE/HIGHLY SHEARED MOIST SECTOR IN PLACE ALONG/SOUTH OF A MODIFYING WEST-EAST OUTFLOW BOUNDARY /NOW AN EFFECTIVE WARM FRONT/ ACROSS FAR NORTHERN PORTIONS OF AL/MS. EXTREME LOW LEVEL SHEAR...VIA LONG/CURVING LOW LEVEL HODOGRAPHS...WILL REMAIN HIGHLY CONDUCIVE FOR SUPERCELLS CAPABLE OF LONG-TRACK STRONG/VIOLENT TORNADOES INTO THIS EVENING AMID 0-1 KM SRH OF 300-500 M2/S2 OR GREATER /ESPECIALLY NEAR THE AFOREMENTIONED NORTHERN MS AND AL BOUNDARY/.

Mesoscale Discussion #0632


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 272138Z - 272215Z

   

A NEW TORNADO WATCH IS BEING COORDINATED WITH AFFECTED WFOS AND WILL BE ISSUED SHORTLY FOR MUCH OF CENTRAL AND ERN KY INTO SERN IND...AND PARTS OF WV AND SWRN VA.  ONGOING TORNADO THREAT S OF THIS REGION IS EXPECTED TO SPREAD NNEWD INTO THE EVENING.

   

LATE AFTERNOON SURFACE ANALYSIS INDICATED AN AREA OF LOW PRESSURE LOCATED OVER SERN MO...WITH THIS FEATURE EXPECTED TO UNDERGO FURTHER INTENSIFICATION TRACKING TOWARD INDIANA AS THE ATTENDANT PROGRESSIVE OZARKS SHORTWAVE TROUGH TAKES ON A NEGATIVE TILT TRACKING NEWD. DESPITE WEAKER INSTABILITY IN PLACE ACROSS THE DISCUSSION AREA...A STRENGTHENING LOW LEVEL JET INTO KY/SRN IND/SRN OH BY EARLY EVENING AS A 100 KT SWLY MIDLEVEL JET NOSES INTO THIS REGION WILL AID IN DESTABILIZATION.  THIS COMBINED WITH INCREASING LOW LEVEL SHEAR/300-500 M2 PER S22/ INTO THE EVENING WILL BE VERY FAVORABLE FOR STORM ROTATION...SUPERCELLS PRODUCING TORNADOES.

Mesoscale Discussion #0634


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 232...235...CONTINUES.

   

PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCHES 232/235 CONTINUE UNTIL 00Z/03Z RESPECTIVELY.

   

A TORNADO OUTBREAK WILL CONTINUE INTO THIS EVENING ACROSS MUCH OF MS/AL INTO NORTHWEST GA. THIS IS AN EXTREMELY DANGEROUS/LIFE-THREATENING SITUATION! CITIES AND AREAS AT GREATEST RISK INCLUDE BIRMINGHAM...HUNTSVILLE...THE I-59 CORRIDOR OF NORTHERN AL...AND I-65 NEAR/NORTH OF BIRMINGHAM.

   

A NUMBER OF SEMI-DISCRETE/LONG-LIVED TORNADIC SUPERCELLS CONTINUE TO FORM WITHIN A PRE-DRYLINE/PRE-COLD FRONTAL WARM SECTOR FROM SOUTH-CENTRAL MS NORTHEASTWARD INTO MUCH OF NORTHERN AL. OTHER TORNADIC STORMS CONTINUE TO INTERACT WITH A MODIFYING EFFECTIVE WARM FRONTAL-TYPE BOUNDARY ACROSS FAR NORTHERN AL IN THE GENERAL VICINITIES OF DECATUR/HUNTSVILLE.

   

THE SPATIALLY WIDE WARM SECTOR IS VERY UNSTABLE AMID MIDDLE-UPPER 60S F SURFACE DEWPOINTS...WITH LOWER 70S F SURFACE DEWPOINTS ACROSS PORTIONS OF SOUTHERN/MS. MLCAPE VALUES ARE AS HIGH AS 2000-4000 J/KG WITHIN THE WEAKLY CAPPED WARM SECTOR.

   

RECENT REGIONAL WSR-88D VWP DATA IS INDICATIVE OF AN INCREASE IN LOW LEVEL WIND SPEEDS/HODOGRAPH CURVATURE OVER THE PAST FEW HOURS...WITH 0-1 KM SRH VALUES NOW ESTIMATED TO BE IN EXCESS OF 300-400 M2/S2 AND 0-3 KM SRH IN EXCESS OF 600 M2/S2 PER BIRMINGHAM/HUNTSVILLE WSR-88D VWPS. THIS WILL REMAIN HIGHLY FAVORABLE FOR LONG-LIVED STRONG/POTENTIALLY VIOLENT TORNADOES WITH ANY SUSTAINED SUPERCELLS WITHIN THE BROAD/VOLATILE WARM SECTOR INTO THIS EVENING.

   

WHILE STRONG TORNADOES WILL BE POSSIBLE WITH ANY SUSTAINED SUPERCELLS WITHIN PDS TORNADO WATCH 232/235...THE RELATIVELY HIGHEST CONCERN OVER THE NEXT FEW HOURS WOULD APPEAR TO BE ACROSS WEST-CENTRAL AL AND NORTHERN HALF OF AL INTO FAR NORTHWEST GA. HERE...IN ADDITION TO THE AFOREMENTIONED RESIDUAL SURFACE BOUNDARY...RELATIVELY STRONG/BACKED LOW LEVEL FLOW IS EVIDENT IN 21Z SUBJECTIVE ANALYSIS AMID A RELATIVE MAXIMA OF 2-HR PRESSURE FALLS...ESPECIALLY ALONG/NORTH OF I-20 IN NORTHERN AL.

Mesoscale Discussion #0636


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 238 CONTINUES.

   

PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCH 238 CONTINUES UNTIL 05Z ACROSS MIDDLE/EASTERN TN. THE POTENTIAL FOR TORNADOES...INCLUDING STRONG TORNADOES...WILL ONLY INCREASE THROUGH EARLY/MID EVENING. THE RELATIVELY HIGHEST TORNADIC POTENTIAL INVOLVES SOUTHERN MIDDLE TN/SOUTHEAST TN INCLUDING THE CHATTANOOGA VICINITY AND I-24/I-75 CORRIDORS.

   

A COMPLEX CONVECTIVE MODE INCLUDING EMBEDDED TORNADIC SUPERCELLS CONTINUE TO DEVELOP/QUICKLY SPREAD NORTHEASTWARD ACROSS PDS TORNADO WATCH 238. OF CONCERN...THE AIRMASS ALONG A PRIOR OUTFLOW BOUNDARY ALONG THE TN/AL BORDER CONTINUES TO RECOVER...WITH A CONTINUED LIKELY NORTHWARD ADVANCEMENT INTO THE SOUTHERN PART OF MIDDLE TN AS WELL AS MUCH OF EASTERN TN THIS EVENING. ACCORDINGLY...RICHER LOW LEVEL MOISTURE /LOWER-MIDDLE 60S F SURFACE DEWPOINTS/ WILL CONTINUE TO SURGE NORTH-NORTHEASTWARD...HEIGHTENING TORNADO POTENTIAL ESPECIALLY ACROSS SOUTHEAST TN. ADDITIONALLY...RAPID AIRMASS RECOVERY/DESTABILIZATION CONTINUES TO OCCUR UPSTREAM ACROSS WESTERN TN BENEATH THE MID LEVEL DRYSLOT...AND THIS WILL FURTHER AID DESTABILIZATION INTO MIDDLE TN THIS EVENING. WITH SUPERCELLS REMAINING LIKELY INTO THIS EVENING...EXTREME SHEAR/LOW LEVEL SHR WILL BE HIGHLY FAVORABLE FOR TORNADIC SUPERCELLS...INCLUDING THE POSSIBILITY OF STRONG TORNADOES.

Mesoscale Discussion #0637


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 272241Z - 272315Z

   

A NEW TORNADO WATCH IS BEING COORDINATED TO THE EAST OF WW/S 235 AND 238.  THIS NEW WATCH WILL LIKELY BE A PDS WATCH.

   

STRENGTHENING SLY LOW LEVEL WINDS /50-60 KT/ THIS EVENING ACROSS ERN AL INTO CENTRAL/NRN GA TO WRN PARTS OF SC/NC WILL MAINTAIN A MOIST AIR MASS /SURFACE DEWPOINTS RISING INTO THE MID 60S/ AND SUPPORTING MLCAPE 1000-2000 J/KG.  THIS COMBINED WITH INCREASING SWLY MIDLEVEL WINDS ATOP THE LOW LEVEL WINDS WILL SUPPORT STRONG EFFECTIVE BULK SHEAR /50-70 KT/ FOR DISCRETE SUPERCELLS AS ACTIVITY NOW LOCATED OVER AL AND ERN TN DEVELOPS DOWNSTREAM.

Mesoscale Discussion #0640


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 235 CONTINUES.

   

PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCH 235 CONTINUES UNTIL 03Z.

   

A HIGH-END TORNADO OUTBREAK WILL CONTINUE INTO THIS EVENING ACROSS A LARGE PART OF CENTRAL/NORTHEAST AL AND NORTHWEST GA. THIS IS AN EXTREMELY DANGEROUS AND LIFE-THREATENING SITUATION! CITIES AND AREAS AT GREATEST RISK INCLUDE BIRMINGHAM...THE I-59 CORRIDOR OF WESTERN/NORTHEAST AL...I-65 ACROSS NORTHERN/CENTRAL AL...AND I-20.

   

23Z SURFACE ANALYSIS CONTINUES TO REFLECT A HIGHLY FAVORABLE ENVIRONMENT FOR TORNADIC SUPERCELLS...WITH RELATIVELY STRONG SOUTHERLY LOW LEVEL WINDS COINCIDENT WITH NEAR 70F SURFACE DEWPOINTS ESPECIALLY WITHIN AN AXIS FROM EAST-CENTRAL MS INTO WEST-CENTRAL TO NORTHEAST AL/NORTHWEST GA. IN PROXIMITY TO DESTRUCTIVE TORNADIC SUPERCELL NEAR/NORTH OF BIRMINGHAM...WSR-88D VWP DATA NOW REFLECTS 0-1 KM SRH IN EXCESS OF 600 M2/S2. A SEMI-DISCRETE/SUSTAINED SUPERCELLULAR MODE...COINCIDENT WITH THE GREATEST INGREDIENTS FOR STRONG/VIOLENT TORNADOES...IS EXPECTED TO REMAIN ACROSS WEST-CENTRAL TO NORTHEAST/EAST-CENTRAL AL AND NORTHWEST GA THROUGH EARLY EVENING. A CORRIDOR OF ROUGHLY 50 MILES EITHER SIDE OF I-59...AS WELL AS THE GENERAL VICINITY OF I-20...REMAINS OF PARTICULARLY HIGH CONCERN FOR LONG-LIVED/DESTRUCTIVE TORNADIC SUPERCELLS.

   

ANOTHER RELATIVELY CONCENTRATED AREA OF HIGH SHORT-TERM CONCERN WILL REMAIN ACROSS FAR NORTHERN AL IN VICINITY OF A RECOVERING OUTFLOW BOUNDARY...WHILE STORMS ALONG THE EASTWARD-ADVANCING PRE-FRONTAL TROUGH/DRYLINE OTHERWISE INCREASE AND GROW UPSCALE/MERGE WITH LEADING SEMI-DISCRETE STORMS. THIS MORE LINEAR EVOLUTION WILL LIKELY TEMPER THE HIGH-END TORNADO POTENTIAL WITH TIME ACROSS NORTHERN AL...BUT THE RISK FOR DAMAGING WINDS/ISOLATED TORNADOES WILL NONETHELESS PERSIST THIS EVENING.

Mesoscale Discussion #0642


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 235 CONTINUES.

   

PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCH 235 CONTINUES UNTIL 03Z...WITH A CONTINUED HIGH-END RISK FOR STRONG/PERHAPS VIOLENT TORNADOES ESPECIALLY ACROSS A LARGE PART OF EAST-CENTRAL/SOUTH-CENTRAL AL INTO NORTHWEST GA. GIVEN A SCHEDULED 03Z EXPIRATION OF TORNADO WATCH 235...EARLY INDICATIONS ARE THAT A REPLACEMENT TORNADO WATCH WILL LIKELY BE NEEDED. THIS REMAINS A POTENTIALLY LIFE-THREATENING SCENARIO. NOT SURPRISING GIVEN A NUMBER OF DESTRUCTIVE TORNADOES SINCE THIS AFTERNOON...THE 00Z OBSERVED BIRMINGHAM RAOB SAMPLED A CLASSIC STRONG TORNADO ENVIRONMENT/PARAMETER SPACE...HIGHLIGHTED BY HIGH BOUNDARY LAYER MOISTURE CONTENT AND VERY STRONG 0-1 KM SRH OF 450 M2/S2 VIA A LONG CURVING HODOGRAPH WITHIN THE LOWEST 1-2 KM. WITH TIME...OBSERVATIONAL TRENDS/SHORT TERM GUIDANCE SUGGEST THE STRONGEST 1-2 KM FLOW WILL CONTINUE TO SHIFT EAST-NORTHEASTWARD ACROSS EASTERN AL INTO NORTHERN GA/THE SOUTHERN APPALACHIANS VICINITY. THERMODYNAMICALLY...THE BOUNDARY LAYER WILL BE VERY SLOW TO DECOUPLE AFTER DARK GIVEN THE HIGH MOISTURE CONTENT...AMID LOWER 70S F SURFACE DEWPOINTS AND 16 G/KM MEAN MIXING RATIO PER THE 00Z BIRMINGHAM RAOB.

   

OF NOTE...ONGOING TORNADIC SUPERCELLS ASIDE...SHORT TERM OBSERVATIONAL TRENDS IMPLY THAT ADDITIONAL STORMS/SUPERCELLS ARE LIKELY TO CONTINUE TO DEVELOP/INCREASE IN THE SHORT-TERM ACROSS SOUTH-CENTRAL/EAST-CENTRAL AL AMID A ZONE OF SHARPENING LOW LEVEL CONFLUENCE. THIS WOULD INCLUDE THE VICINITY OF MONTGOMERY AND NEARBY I-65/I-85 GENERAL VICINITIES. ACCORDINGLY...SUSTAINED/RELATIVELY DISCRETE TORNADIC SUPERCELLS...WITH CONTINUED STRONG/PERHAPS VIOLENT TORNADO POTENTIAL...ARE LIKELY TO PERSIST WITHIN A WSW-ENE ORIENTED BROAD CORRIDOR ACROSS A LARGE PART OF CENTRAL/PORTIONS OF SOUTHERN AL INTO NORTHWEST/WEST-CENTRAL GA THIS EVENING.

Mesoscale Discussion #0645


CONCERNING...TORNADO WATCH 240...

   

VALID 280212Z - 280315Z

   

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 240 CONTINUES.

   

RECENT RADAR/SATELLITE TRENDS INDICATE SEVERE THREAT HAS BECOME INCREASINGLY LOCALIZED ACROSS CNTRL VA...WITH A LONE SUPERCELL NOW IN CULPEPER COUNTY. HOWEVER...LONG-TRACK SUPERCELLS ARE APPROACHING THE WRN EXTENT OF WW 240 ACROSS SWRN VA/NWRN NC/SERN WV. SURFACE DEW POINTS CONTINUE TO INCREASE ACROSS THIS REGION JUST AHEAD OF THESE CELLS. MODIFIED 00Z RNK RAOB SUGGESTS MODEST SURFACE-BASED INSTABILITY WOULD REMAIN IN PLACE WITHIN A VERY STRONGLY SHEAR ENVIRONMENT...CONDUCIVE TO ALL FORMS OF SEVERE WEATHER THROUGH THE OVERNIGHT.

Mesoscale Discussion #0648


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 238...241...CONTINUES.

   

A NEW TORNADO WATCH WILL BE NEEDED FOR PARTS OF THIS REGION GIVEN THE EXPIRATION OF WW 241 AT 06Z.  LOCAL WFO EXTENSION OF WW 238 MAY BE NEEDED AS THE STORM OVER SEVIER COUNTY TN REACHES FAR NERN TN BETWEEN 05-0530Z.

   

THE LIKELIHOOD FOR DISCRETE SUPERCELLS PRODUCING TORNADOES CONTINUES ACROSS THE VALID PORTIONS OF PDS /PARTICULARLY DANGEROUS SITUATION/WATCHES 238 AND 241 LATE THIS EVENING INTO THE EARLY OVERNIGHT PERIOD.  THIS INCLUDES ERN AL THROUGH CENTRAL AND NRN GA TO FAR ERN TN...UPSTATE SC AND WRN NC.

   

LATE EVENING SURFACE ANALYSIS SHOWED AN AREA OF LOW PRESSURE OVER CENTRAL INDIANA WITH A COLD FRONT TRAILING SWD THROUGH MIDDLE TN AND NERN AL TO SERN MS.  REGIONAL RADAR IMAGERY INDICATED SEVERAL DISCRETE SUPERCELLS ACROSS THE DISCUSSION AREA WITH THIS ACTIVITY LOCATED ALONG AT LEAST TWO PRE-FRONTAL WIND SHIFTS/CONVERGENCE ZONES.  THE WARM SECTOR REMAINS MODERATELY UNSTABLE FROM NRN GA SWD AND MARGINALLY UNSTABLE ACROSS FAR WEST CENTRAL NC.  WRN EXTENT OF STRONGER INSTABILITY IN LEE OF THE APPALACHIANS DOES EXIST OVER THE NERN PART OF WW 241.  STRONG DEEP LAYER WIND FIELDS REMAIN SUPPORTIVE OF SUPERCELLS WITH THE STRENGTH OF THE LLJ /55-70 KT/FROM ERN AL/WRN GA TO ERN KY AND WV WILL MAINTAIN STRONG LOW LEVEL SHEAR FOR LOW LEVEL ROTATION/TORNADIC THREAT.

Mesoscale Discussion #0843


THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 318...319...CONTINUES.

   

LTH PROFILER/AREA VWP/S INDICATE LLJ IS INCREASING ACROSS WRN/NRN MO...WITH FLOW AT 1 KM AGL APPROACHING 30 KT. THIS IS AIDING IN STRENGTHENING LOW-LEVEL SHEAR PROFILES...WITH 0-1 KM BULK SHEAR NEAR 30 KT/0-1 KM SRH FROM 100-150 M2 S-2...AND FORECAST BY THE RUC TO INCREASE TO 250 M2 S-2 BY 01Z. PRIMARY LIMITING FACTOR FOR MORE ROBUST TORNADO THREAT IS FAIRLY LARGE SURFACE DEWPOINT DEPRESSIONS/AROUND 18F/...WHICH WILL ENHANCE POTENTIAL FOR STRONG COLD POOLS. HOWEVER...QUASI-DISCRETE SUPERCELLS OCCURRING ACROSS NWRN MO/NERN KS MAY EXPERIENCE SOME INCREASE IN TORNADO POTENTIAL DURING THE NEXT FEW HRS. OTHERWISE...THREAT FOR LARGE/VERY LARGE HAIL AND DAMAGING WIND GUSTS CONTINUES TO EXIST ACROSS WW 319...AND MAINLY ERN PORTIONS OF WW 318.


**This MCD preceded the Reading, Kansas EF3 tornado

Mesoscale Discussion #0847


CONCERNING...OUTLOOK UPGRADE 

   

VALID 220941Z - 221145Z

   

AN UPGRADE TO A CATEGORICAL MODERATE RISK IS ANTICIPATED WITH THE DAY 1 OUTLOOK UPDATE AT 13Z. THIS WILL LIKELY INCLUDE PORTIONS OF NORTHEAST MO/EASTERN IA/SOUTHEAST MN INTO WESTERN/NORTHERN IL AND WESTERN/SOUTHERN WI...WITH THE PRIMARY SEVERE THREAT EXPECTED LATER THIS AFTERNOON/EVENING. FOR ADDITIONAL METEOROLOGICAL DISCUSSION...SEE THE DAY 1 OUTLOOK THAT WILL BE ISSUED BY AROUND 13Z. A PUBLIC SEVERE WEATHER OUTLOOK /PWO/ WILL ALSO BE ISSUED EARLY THIS MORNING.

Mesoscale Discussion #0849


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 221553Z - 221800Z

   

CONDITIONS WILL BECOME QUITE FAVORABLE FOR SUPERCELLS AND TORNADOES LATER THIS AFTERNOON...AND ONE OR MORE TORNADO WATCHES ARE LIKELY BY MIDDAY.

   

VISIBLE SATELLITE IMAGERY SHOWS A WELL DEFINED DRYLINE ACROSS ERN KS...NWRN MO AND INTO IA WHERE MORE EXTENSIVE CLOUD COVER EXISTED AS A RESULT OF THE UPPER VORT. MEANWHILE...A PSEUDO-WARM FRONT EXTENDING FROM CNTRL IA SEWD INTO CNTRL IL...WITH MID TO UPPER 60S F DEWPOINTS S OF THIS BOUNDARY. 

   

MORNINGS SOUNDINGS SHOWED CLASSIC LOADED GUN WITH SUBSTANTIAL BOUNDARY LAYER MOISTURE IN PLACE BENEATH A BREAKABLE CAPPING INVERSION. THE STRONGEST FORCING FOR ASCENT WILL DEVELOP FIRST ACROSS MN/IA/WI AS THE UPPER LOW CONTINUES EWD. NRN EXTENT OF THREAT AREA WILL COINCIDE WITH WARM FRONT. OTHER DEVELOPMENT WILL OCCUR SWD ALONG THE DRYLINE INTO MO AND FAR ERN KS WHERE A SUBSTANTIAL CU FIELD WAS ALREADY DEVELOPING AND WITH 3000-4000 J/KG MUCAPE. SHEAR PROFILES ARE FAVORABLE FOR SUPERCELLULAR STORM MODE CAPABLE OF A FEW STRONG TORNADOES AND VERY LARGE HAIL.

Mesoscale Discussion #0853


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 221806Z - 222000Z

   

A TORNADO WATCH WILL BE ISSUED SHORTLY.

   

AN EXTREMELY UNSTABLE AIR MASS HAS DEVELOPED E OF THE DRYLINE WITH DEWPOINTS NEAR 70 F BENEATH STEEP MID LEVEL LAPSE RATES. NEARLY ALL CONVECTIVE INHIBITION HAS BEEN ERODED...THUS EXPECTED CU ALONG THE DRYLINE TO ERUPT INTO INTENSE SUPERCELLS. EXTREMELY LARGE HAIL IS LIKELY...AND ALTHOUGH LOW LEVEL SHEAR IS A BIT MARGINAL...IT WILL BE MORE THAN SUFFICIENT FOR TORNADOES GIVEN EXTREME INSTABILITY.

Mesoscale Discussion #0858


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 322...323...327...CONTINUES.

   

THE TORNADO THREAT INCREASING ACROSS THE AREA.

   

LATEST RADAR TRENDS SHOW STORMS BEGINNING TO SHOW MORE CLASSIC SUPERCELL STRUCTURE WITH INTENSIFYING MESOCYCLONES. NOW THAT STORMS HAVE BECOME ESTABLISHED...THEY WILL BE ABLE TO TAKE ADVANTAGE OF THE ENVIRONMENT WHICH IS QUITE UNSTABLE WITH AMPLE SHEAR FOR TORNADOES. AREA WIND PROFILERS AND VADS SHOW A FAVORABLE SHEAR ENVIRONMENT FOR STRONG TORNADOES...ESPECIALLY OVER NERN IA..SERN MN...WRN WI...AND EVENTUALLY FAR NWRN IL. THE ENVIRONMENT WILL CONTINUE TO BECOME MORE FAVORABLE FARTHER E INTO CNTRL WI AND NRN IL AS MID 60S BOUNDARY LAYER DEWPOINTS STREAM NWD

Mesoscale Discussion #0862


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 325 CONTINUES.

   

VIGOROUS CONVECTION CONTINUE TO INTENSIFY ALONG THE DRYLINE FROM WRN MO INTO SERN KS. A MODIFIED 19Z SGF SOUNDING USING OBSERVED SURFACE OBSERVATIONS ALONG THE DRYLINE YIELDS OVER 5000 J/KG MUCAPE WITH A 300 MB LI OF -19C. ALSO DEPICTED IN THIS SOUNDING...AND ON NDS AND CNW PROFILERS...IS 40-50 KT MID LEVEL FLOW ATOP VEERING LOW LEVEL FLOW...MORE THAN SUFFICIENT FOR SUPERCELLS. EXISTING STORMS WILL PERSIST WITH AN EXTREME HAIL THREAT AS WELL AS THE POSSIBILITY OF CYCLIC TORNADOES.

   

TO THE S...A SUBSTANTIAL CU FIELD REMAINS OVER NERN OK...AND SWD ACROSS ERN OK WHERE DEWPOINTS ARE IN EXCESS OF 72 F. HERE...SBCAPE IS AVERAGING 5500-6000 J/KG. HKL AND PRC PROFILERS ALSO INDICATE INCREASING MID TO UPPER LEVEL FLOW TO 50-60 KTS ABOVE 9 KM. STRONG HEATING PERSISTS NEAR THE DRYLINE...ALTHOUGH CONVERGENCE IS WEAK. TOWERING CU PERSIST ALONG THE DRYLINE. ANY ROBUST STORMS THAT DO FORM WILL CERTAINLY PRODUCE VERY LARGE HAIL AND HAVE A THREAT OF TORNADOES.

Mesoscale Discussion #0867


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 325 CONTINUES.

   

AT 2245-23Z...REGIONAL AND HI-RES RADAR IMAGERY SHOW A CLUSTER OF HP SUPERCELLS MOVING E-SE AT AROUND 30 KT. MOST SIGNIFICANT STORM /WITH A HISTORY OF PRODUCING A TORNADO/ IN THIS CLUSTER WAS LOCATED NEAR JOPLIN AT 2248Z. SGF VWP SHOWS ENLARGED LOW-LEVEL HODOGRAPH STRUCTURE...WITH 0-1 KM SRH NEAR 200 M2 S-2. GIVEN STRONG SHEAR PROFILES RESIDE DOWNSTREAM OVER SWRN MO...ALONG WITH AXIS OF MLCAPE VALUES FROM 2500-4000 J/KG...TORNADO THREAT /POTENTIALLY STRONG/ ALONG WITH VERY LARGE HAIL SHOULD PERSIST AS HP SUPERCELL CLUSTER MOVES ACROSS THE REMAINDER OF SWRN MO. FARTHER N OVER CNTRL MO...CLUSTER OF STORMS WAS MOVING E ACROSS AN ENVIRONMENT CHARACTERIZED BY STRONG INSTABILITY AND FAVORABLE SHEAR PROFILES FOR SUPERCELLS POSING A THREAT FOR TORNADOES...LARGE HAIL AND DAMAGING WINDS. 

   

MEANWHILE OVER NERN OK...SUSTAINED STORM DEVELOPMENT APPEARS TO BE TAKING PLACE BASED ON RECENT REGIONAL REFLECTIVITY. WITH SURFACE CONDITIONS CHARACTERIZED BY TEMPERATURES IN THE MID 80S AND DEWPOINTS IN THE LOW 70S...AND 700-500 MB LAPSE RATES AROUND 7 C/KM...EXTREME INSTABILITY RESIDES AHEAD OF THIS NEW DEVELOPMENT/MLCAPE VALUES NEAR 4000 J PER KG/. AREA VWP/S AND RUC SOUNDINGS SHOW FAVORABLE WIND PROFILES FOR SUPERCELL DEVELOPMENT AS THIS ACTIVITY MOVES DOWNSTREAM ACROSS NERN OK INTO NWRN AR...WITH THE POTENTIAL FOR VERY LARGE HAIL AND TORNADOES CONTINUING INTO THE EVENING HRS.

   

OVER S-CNTRL OK...LEFT MOVING SUPERCELL IS RAPIDLY MOVING N TOWARD THE SWRN CORNER OF WW 325. THIS STORM WILL POSE A THREAT FOR LARGE HAIL IF IT PERSISTS INTO E-CNTRL/NERN OK.

Mesoscale Discussion #0925


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 241718Z - 241845Z

   

STORM INITIATION IS EXPECTED ACROSS WRN OK AND NW TX OVER THE NEXT HOUR. SUPERCELLS SHOULD RAPIDLY DEVELOP WITH A THREAT FOR LARGE HAIL AND TORNADOES. A TORNADO WATCH WILL LIKELY NEED TO BE ISSUED BY 18Z.

   

   

SFC ANALYSIS SHOWS A 997 MB LOW IN THE NRN TX PANHANDLE WITH A DRYLINE EXTENDING SWD FROM THE LOW ACROSS FAR WRN OK INTO WEST TX. THE DRYLINE IS STARTING TO ADVANCE EWD WITH VISIBLE SATELLITE IMAGERY SHOWING AN EXPANDING FIELD OF CUMULUS FROM I-40 IN WRN OK SWD TO NEAR SAN ANGELO IN WCNTRL TX. AS FURTHER DESTABILIZATION OCCURS THIS AFTERNOON AND THE CAP WEAKENS...RAPID CELL INITIATION IS EXPECTED TO OCCUR ALONG THIS CORRIDOR. AS THIS OCCURS...A 50 TO 65 KT MID-LEVEL JET EJECTING NEWD TOWARD THE SRN PLAINS WILL CREATE STRONG DEEP LAYER SHEAR PROFILES VERY FAVORABLE FOR SUPERCELLS. AS STORMS INTENSIFY...VERY LARGE HAIL GREATER THAN 2 INCHES IN DIAMETER WILL BECOME LIKELY. IN ADDITION...A 30 TO 40 KT LOW-LEVEL JET IS IN PLACE ACROSS NW TX AND WRN OK. AS THIS FEATURE STRENGTHENS...LOW-LEVEL SHEAR WILL BECOME VERY FAVORABLE FOR TORNADOES. WITH 0-3 KM STORM RELATIVE HELICITIES INCREASING INTO THE 450 TO 600 M2/S2 RANGE...LONG-TRACK STRONG TORNADOES ARE EXPECTED TO OCCUR LATE THIS AFTERNOON INTO EARLY THIS EVENING.

Mesoscale Discussion #0927


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 241759Z - 241930Z

   

A SEVERE THREAT SHOULD DEVELOP ACROSS WRN AND CNTRL KS AS STORM INITIATE AND INCREASE IN COVERAGE THIS AFTERNOON. THE ENVIRONMENT WILL SUPPORT A THREAT FOR LARGE HAIL AND TORNADOES. THE THREAT FOR TORNADOES SHOULD INCREASE LATE THIS AFTERNOON AS THE LOW-LEVEL JET STRENGTHENS. A TORNADO WATCH WILL LIKELY BECOME NECESSARY BY 19Z TO 20Z ACROSS THE REGION.

   

SCATTERED STRONG THUNDERSTORMS ARE CURRENTLY ONGOING IN ERN CO TO THE NW OF A SFC LOW IN THE NRN TX PANHANDLE. THIS ACTIVITY WILL CONTINUE TO INCREASE IN COVERAGE EXPANDING EWD ACROSS WRN AND NCNTRL KS THIS AFTERNOON AS A SHORTWAVE TROUGH MOVES OUT INTO THE SRN AND CNTRL HIGH PLAINS. AHEAD OF THE SHORTWAVE TROUGH...THE EXIT REGION OF A WELL-DEVELOPED 70 TO 85 KT MID-LEVEL JET WILL EJECT NEWD ACROSS THE CNTRL PLAINS CREATING STRONG DEEP LAYER SHEAR PROFILES AND ENHANCING LIFT. THIS COMBINED WITH MODERATE DESTABILIZATION AND VERY STEEP MID-LEVEL LAPSE RATES WILL BE FAVORABLE FOR THE DEVELOPMENT OF SUPERCELLS WITH LARGE HAIL. IN ADDITION...A 35 TO 45 LOW-LEVEL JET IN NRN OK IS FORECAST TO EXPAND NWWD INTO WCNTRL KS LATE THIS AFTERNOON. THIS WILL CREATE A LOW-LEVEL SHEAR ENVIRONMENT INCREASINGLY FAVORABLE FOR TORNADOES. THE MORE DOMINANT SUPERCELLS MAY HAVE A THREAT FOR STRONG TORNADOES ESPECIALLY ACROSS CNTRL KS WHERE MODERATE INSTABILITY IS ALREADY IN PLACE.

Mesoscale Discussion #0930


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 241915Z - 242045Z

   

A SEVERE THREAT WILL LIKELY DEVELOP ACROSS THE CONCHO VALLEY INTO CNTRL TX THIS AFTERNOON. AS CELLS INITIATE...SUPERCELL DEVELOPMENT WILL LIKELY OCCUR WITH A POTENTIAL FOR LARGE HAIL AND TORNADOES. A TORNADO WATCH WILL LIKELY BE NECESSARY OVER THE NEXT HOUR ACROSS THE REGION.

   

A DRYLINE IS CURRENTLY LOCATED ACROSS WEST TX AND IS STARTING TO ADVANCE MORE QUICKLY EWD. VISIBLE SATELLITE IMAGERY SHOWS CUMULUS JUST AHEAD OF THE DRYLINE FROM NEAR WICHITA FALLS SWD TO NEAR SAN ANGELO. THE CAPPING INVERSION IS NOW GONE ACROSS THE MCD AREA AND STORM INITIATION WILL BECOME INCREASINGLY LIKELY AS CONVERGENCE INCREASES ALONG THE DRYLINE. MESOANALYSIS SHOWS STRONG INSTABILITY IN PLACE WITH MLCAPE VALUES FROM 3000 TO 4000 J/KG. IN ADDITION...PROFILER DATA SUGGEST 0-6 KM SHEAR VALUES ARE AROUND 40 KT. THE SHEAR SHOULD RAPIDLY INCREASE AS A 65 TO 80 KT MID-LEVEL JET MOVES INTO THE REGION FROM THE WEST MAKING CONDITIONS VERY FAVORABLE FOR SUPERCELLS. THE MORE DOMINANT SUPERCELLS SHOULD HAVE A THREAT FOR VERY LARGE HAIL OF GREATER THAN 2 INCHES IN DIAMETER. IN ADDITION...STRENGTHENING LOW-LEVEL SHEAR LATE THIS AFTERNOON SHOULD ALSO RESULT IN A TORNADO THREAT WITH AN ISOLATED STRONG TORNADO THREAT POSSIBLE AS WELL.

Mesoscale Discussion #0932


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 241935Z - 242100Z

   

A SEVERE THREAT WILL LIKELY DEVELOP ACROSS NRN OK AND SRN KS LATE THIS AFTERNOON AS STORMS INITIATE AND MOVE INTO THE REGION FROM THE SOUTHWEST. A TORNADO WATCH WILL BE REQUIRED PRIOR TO 21Z.

   

SFC ANALYSIS SHOWS A RAPIDLY DEEPENING 994 MB LOW ACROSS THE ERN OK PANHANDLE WITH A DRYLINE MOVING EWD ACROSS WRN OK. THUNDERSTORMS ARE DEVELOPING ALONG THE DRYLINE AHEAD OF A STRONGLY UNSTABLE AIRMASS WHERE MESOANALYSIS SHOWS MLCAPE VALUES RANGING FROM 3500 TO 4500 J/KG. IN ADDITION...A WELL-DEFINED MID-LEVEL JET 70 TO 85 KT ENTERING WEST TX WILL EJECT NEWD ACROSS THE MCD AREA LATE THIS AFTERNOON INTO EARLY THIS EVENING. THIS WILL CREATE VERY FAVORABLE DEEP LAYER SHEAR PROFILES FOR SUPERCELLS. THIS POTENTIAL WILL INCREASE AS THE SUPERCELLS CURRENTLY IN WRN OK MOVE NEWD INTO SRN KS OVER THE NEXT COUPLE OF HOURS. AS THE UPPER-LEVEL TROUGH MOVES INTO THE REGION FROM THE WEST...THE LOW-LEVEL JET WILL QUICKLY STRENGTHEN RESULTING IN VERY FAVORABLE CONDITIONS FOR TORNADOES. A THREAT FOR STRONG LONG-TRACK TORNADOES WILL LIKELY EXIST WITH THE MORE DOMINANT SUPERCELLS WITH THIS THREAT INCREASING WITH TIME.

Mesoscale Discussion #0934


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 356 CONTINUES.

   

SUPERCELLS CAPABLE OF PRODUCING STRONG TO VIOLENT TORNADOES AND VERY LARGE HAIL WILL MOVE INTO CNTRL OK AND N-CNTRL TX...LIKELY AFFECTING THE OKLAHOMA CITY AND DALLAS-FORT WORTH METRO AREAS BETWEEN 5 AND 7 PM THIS EVENING. GREATEST THREAT CURRENTLY APPEARS ACROSS CNTRL AND S-CNTRL OK.

   

A LINE OF DISCRETE SUPERCELLS THAT INITIATED ALONG THE DRYLINE EXTENDS FROM NEAR ENID IN N-CNTRL OK SWD TO NEAR MINERAL WELLS IN N-CNTRL TX. THE DOWNSTREAM ATMOSPHERE IS VERY UNSTABLE WITH 3000-4000 J/KG MLCAPE...VERY STEEP LAPSE RATES AND A MOIST BOUNDARY LAYER. THE TWIN LAKES VWP ALREADY INDICATE VERY STRONG /60-70 KT/ SFC-6 KM SHEAR AND LARGE HODOGRAPHS WITH 300+ M2/S2 0-1 KM STORM RELATIVE HELICITY. SEVERAL TORNADOES HAVE ALREADY BEEN CONFIRMED...AND THIS PARAMETER SPACE WILL CONTINUE TO SUPPORT SUPERCELLS CAPABLE OF LONG TRACK...DAMAGING TORNADOES AND VERY LARGE HAIL AS STORMS MOVE THROUGH CNTRL OK AND N-CNTRL TX NEXT FEW HOURS.

Mesoscale Discussion #0938


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 356 CONTINUES.

   

THREAT FOR STRONG TORNADOES...VERY LARGE HAIL AND DAMAGING WIND IS EXPECTED TO PERSIST FROM CNTRL THROUGH ERN OK INTO N-CNTRL TX THE NEXT FEW HOURS.

   

NUMEROUS STORMS INCLUDING A FEW SUPERCELLS CONTINUE FROM N-CNTRL TX THROUGH CNTRL AND E-CNTRL OK. MANY STORMS IN CNTRL OK HAVE BECOME TEMPORARILY LESS ORGANIZED DUE TO DESTRUCTIVE INTERFERENCE ASSOCIATED WITH CELL MERGERS AND OUTFLOW INTERACTIONS. HOWEVER...THE ENVIRONMENT REMAINS SUPPORTIVE OF TORNADOES AND VERY LARGE HAIL WITH LARGE 0-1 KM HODOGRAPHS AND STRONG INSTABILITY...AND SOME STORMS WILL LIKELY REORGANIZE DURING THE EVENING. FARTHER SOUTH STORMS REMAIN MORE DISCRETE ACROSS N-CNTRL TX AND WILL ALSO CONTINUE TO POSE A THREAT FOR VERY LARGE HAIL AND TORNADOES.

Mesoscale Discussion #0945


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 363...364...CONTINUES.

   

THREAT FOR ISOLATED TORNADOES...DAMAGING WIND AND LARGE HAIL WILL LIKELY PERSIST NEXT FEW HOURS AS STORMS MOVE THROUGH WRN AND CNTRL MO...EXTREME ERN OK INTO WRN AR AND NERN TX.

   

AN EXTENSIVE BAND OF STORMS WITH EMBEDDED SUPERCELLS IS ADVANCING EWD THROUGH WRN MO...EXTREME ERN OK...WRN AR AND NERN TX. A STRONG SLY LLJ WILL CONTINUE TO SHIFT EWD THROUGH THE LOWER-MID MS VALLEY IN ASSOCIATION WITH POTENT CNTRL/SRN PLAINS SHORTWAVE TROUGH. THIS WILL MAINTAIN 0-1 KM HODOGRAPHS FAVORABLE FOR TORNADOES AS ACTIVITY CONTINUES EWD INTO A MODERATELY UNSTABLE ENVIRONMENT WHERE MUCAPE REMAINS AROUND 2000 J/KG.

   

SEVERE THREAT WITH STORMS DEVELOPING BEHIND THE LINE ACROSS ERN KS WILL PROBABLY REMAIN SOMEWHAT MARGINAL DUE TO MORE LIMITED INSTABILITY.


**This MCD preceded the Etna, Arkansas EF4 tornado

Mesoscale Discussion #0949


CONCERNING...OUTLOOK UPGRADE 

   

VALID 251231Z - 251330Z

   

AN UPGRADE TO A CATEGORICAL HIGH RISK IS LIKELY WITH THE UPDATED DAY 1 CONVECTIVE OUTLOOK AT 13Z.  THIS WILL LIKELY INCLUDE PORTIONS OF NERN AR / WRN TN / WRN KY / SERN MO / FAR SRN IL AND SWRN IND.  FOR ADDITIONAL METEOROLOGICAL DISCUSSION...SEE THE FORTHCOMING DAY 1 OUTLOOK THAT WILL BE ISSUED BY AROUND 13Z.

Mesoscale Discussion #0952


CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

   

VALID 251454Z - 251630Z

   

STORM INITIATION IS EXPECTED TO OCCUR OVER THE NEXT FEW HOURS IN WRN MO AND WRN AR. AS THE STORMS INTENSIFY...SEVERE THUNDERSTORM DEVELOPMENT WILL BE LIKELY. INITIALLY LARGE HAIL AND WIND DAMAGE WILL BE THE PRIMARY THREATS BUT AS THE STORMS MATURE...A TORNADO THREAT WILL ALSO BECOME LIKELY. WW ISSUANCE SHOULD BECOME NECESSARY ACROSS THE REGION LATE THIS MORNING AS CONFIDENCE INCREASES CONCERNING THE EXACT TIMING OF STORM INITIATION.

   

THE LATEST SFC ANALYSIS SHOWS A 995 MB LOW OVER ERN KS WITH A BROAD WARM SECTOR EXTENDING EWD ACROSS THE SRN HALF OF MO AND ACROSS ALL OF AR INTO MS AND WRN TN. A WEAK CAPPING INVERSION IS ANALYZED ACROSS MUCH OF THE WARM SECTOR BUT THE CAP SHOULD DIMINISH QUICKLY AS SFC TEMPS WARM ALLOWING FOR CONVECTIVE INITIATION. SHORT-TERM MODEL FORECASTS INITIATE SCATTERED THUNDERSTORMS ACROSS SW MO AND WRN AR AROUND 17Z...SPREADING THIS ACTIVITY ENEWD ACROSS SE MO AND NE AR BY EARLY AFTERNOON. STRONG DEEP LAYER SHEAR ASSOCIATED WITH A 65 TO 75 KT MID-LEVEL JET EJECTION ACROSS THE WARM SECTOR WILL PROVIDE CONDITIONS FAVORABLE FOR INTENSE SUPERCELL DEVELOPMENT. INITIALLY...A LARGE HAIL AND WIND DAMAGE THREAT WILL EXIST BUT AS THE STORMS MOVE INTO A 50 TO 60 KT LOW-LEVEL JET...A THREAT FOR TORNADOES WILL ALSO DEVELOP. FORECAST SOUNDINGS ACROSS THE ERN PART OF THE MCD AREA BY 18Z TO 21Z SHOW 0-3 KM STORM RELATIVE HELICITIES IN THE 350 TO 450 M2/S2 RANGE SUGGESTING STRONG TORNADOES WILL BE POSSIBLE THIS AFTERNOON.

Mesoscale Discussion #0953


CONCERNING...OUTLOOK UPGRADE 

   

VALID 251518Z - 251615Z

   

AN EXPANSION OF THE CATEGORICAL HIGH RISK WILL OCCUR WITH THE UPDATED DAY 1 CONVECTIVE OUTLOOK AT 1630Z FOR A POTENTIAL MAJOR TORNADO OUTBREAK. THIS WILL LIKELY INCLUDE ADDITIONAL PORTIONS OF SERN MO...NERN AR...SRN IL/IND...AND WRN KY/TN. PLEASE SEE THE FORTHCOMING DAY 1 OUTLOOK THAT WILL BE ISSUED BY 1630Z FOR FURTHER METEOROLOGICAL DISCUSSION.

Mesoscale Discussion #0954


CONCERNING...SEVERE POTENTIAL...WATCH NEEDED SOON 

   

VALID 251602Z - 251630Z

   

A THREAT FOR TORNADOES...WIND DAMAGE AND LARGE HAIL WILL LIKELY DEVELOP THIS AFTERNOON AS STORMS INITIATE AND INCREASE IN COVERAGE. A PDS TORNADO WATCH IS BEING COORDINATED ATTM.

   

CONVECTIVE INITIATION IS STARTING TO OCCUR ACROSS FAR SRN IL AHEAD OF LEAD SHORTWAVE TROUGH ON THE ERN EDGE OF A CNTRL PLAINS UPPER-LEVEL LOW. VIGOROUS STORMS WILL ALSO INITIATE IN SCNTRL MO AND MOVE INTO THE REGION FROM THE WEST AS A 65 TO 80 KT MID-LEVEL JET EJECTS ENEWD ACROSS THE WARM SECTOR. THIS FEATURE WILL CREATE STRONG DEEP LAYER SHEAR PROFILES WHICH COMBINED WITH MODERATE INSTABILITY WILL BE VERY FAVORABLE FOR SUPERCELL DEVELOPMENT. AS STORM INCREASE IN COVERAGE...A WIDESPREAD SEVERE THREAT IS EXPECTED BY EARLY AFTERNOON. DEVELOPING LINEAR STORMS WILL LIKELY HAVE A THREAT FOR WIND DAMAGE AND LARGE HAIL BUT STORMS THAT REMAIN DISCRETE SHOULD BECOME SUPERCELLS CONTAINING A THREAT FOR TORNADOES. AS A 50 TO 60 KT LOW-LEVEL JET BECOMES MORE FOCUSED THIS AFTERNOON...0-3 KM STORM RELATIVELY HELICITIES WILL INCREASE BECOMING VERY FAVORABLE FOR STRONG LONG-TRACK TORNADOES ESPECIALLY LATER THIS AFTERNOON AS THE MID-LEVEL JET APPROACHES FROM THE SOUTHWEST.

Mesoscale Discussion #0955


CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   

VALID 251652Z - 251815Z

   

DISCRETE SUPERCELLS SHOULD FORM BY MID-AFTERNOON WITH A POTENTIAL THREAT OF LONG-TRACKED/STRONG TORNADOES. A PDS TORNADO WATCH WILL BE REQUIRED...MOST LIKELY BY 18Z.

   

RECENT VISIBLE SATELLITE IMAGERY INDICATES A DEEPENING CU FIELD AND CLOUD STREETS ACROSS MUCH OF AR DOWNSTREAM OF A COLD FRONT THAT EXTENDED FROM FAR SWRN MO INTO NERN TX AS OF 16Z. 12Z WRF-NMM DEPICTS DISCRETE CELLS EMANATING OUT OF THIS CU FIELD BY 19Z...WITH RECENT HRRR RUNS FASTER WITH TSTM INITIATION BUT SIMILAR IN CONVECTIVE MODE. ENVIRONMENT IS PRIMED FOR RAPID EVOLUTION TO SUPERCELLS GIVEN VERY FAVORABLE LOW/MID-LEVEL HODOGRAPHS PER PROFILER AND VWP DATA...AMIDST A BROAD ZONE OF STRONG INSTABILITY WITH MLCAPE AROUND 2500 J/KG. ANY SUPERCELLS DEVELOPING WITHIN A BROAD AXIS OF A 45-55 KT LLJ...POTENTIAL FOR LONG-LIVED/STRONG TORNADOES WILL INCREASE GREATLY TOWARDS MID-AFTERNOON.

Mesoscale Discussion #0957


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 369 CONTINUES.

   

A SEVERE THREAT WILL CONTINUE ACROSS WW 369 WITH TORNADOES AND LARGE HAIL LIKELY WITH THE STRONGER CELLS. THE TORNADO THREAT SHOULD EXPAND NNEWD ACROSS THE VALID PART OF TORNADO WATCH 369. A LOCAL EXTENSION HAS BEEN COORDINATED WITH LOCAL WFO.

   

A LINE OF SUPERCELLS IS ONGOING FROM JUST EAST OF KANSAS CITY  NEAR A 996 MB SFC LOW EXTENDING SSEWD ACROSS CNTRL MO ALONG THE WRN EDGE OF STRONG INSTABILITY. THIS LINE SHOULD CONTINUE EWD ACROSS CNTRL MO. THE MORE INTENSE SUPERCELLS WILL CONTAIN A THREAT FOR TORNADOES...WIND DAMAGE AND LARGE HAIL. A THREAT FOR STRONG TORNADOES WILL EXIST WITH THE MORE INTENSE SUPERCELLS. A SEVERE THREAT SHOULD ALSO EXIST SWWD INTO SW MO WHERE MID-LEVEL FLOW IS QUITE STRONG BENEATH THE NRN EDGE OF AN EJECTION MID-LEVEL JET.

   

FURTHER TO THE NORTH ACROSS NRN MO...MODERATE INSTABILITY IS NOW IN PLACE WITH MESOANALYSIS SHOWING MLCAPE VALUES IN THE 1000 TO 1500 J/KG RANGE. THIS PART OF THE WARM SECTOR IS BENEATH THE NERN EDGE OF UPPER-LEVEL LOW WHERE TEMPS ALOFT ARE QUITE COLD. 500 MB TEMPS OF -15C TO -16C ALONG WITH 30 TO 40 KT OF DEEP LAYER SHEAR SHOULD BE FAVORABLE FOR SUPERCELLS WITH LARGE HAIL. IN ADDITION...SFC WINDS ARE BACKED TO THE EAST ACROSS NRN MO SUGGESTING DIRECTIONAL SHEAR WILL BE FAVORABLE FOR TORNADOES AS WELL.

Mesoscale Discussion #0959


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 369...370...CONTINUES.

   

DISCRETE SUPERCELLS HAVE BEGUN TO INTERACT WITH THE RETREATING SURFACE OUTFLOW BOUNDARY EXTENDING ACROSS EAST CENTRAL MO AND WEST CENTRAL IL.  STRONG HEATING HAS OCCURRED TO THE NORTH OF BOUNDARY...WHERE DEWPOINTS IN THE UPPER 60S ARE YIELDING MLCAPE VALUES OVER 2000 J/KG.  BACKED LOW LEVEL WINDS AND LOCALLY ENHANCED VORTICITY ALONG REMNANT BOUNDARY ARE LIKELY AIDING SUPERCELL STRUCTURES.  LATEST SURFACE ANALYSIS ALSO HINTS AT A WEAK SURFACE MESOLOW NEAR COU...CONTRIBUTING TO ENHANCED LOW LEVEL SHEAR AND PRESSURE FALLS ALONG THE BOUNDARY.  STORMS NOW OVER AUDRAIN/MONTGOMERY/LINCOLN COUNTIES MO ARE SHOWING SIGNIFICANT ROTATION WITH AN ENHANCED RISK OF TORNADOES.  THE THREAT OF TORNADOES AND VERY LARGE HAIL WILL PERSIST IN THIS ZONE FOR THE NEXT FEW HOURS AS DISCRETE STORMS FORM TO THE SOUTH AND TRACK ACROSS THE RETREATING BOUNDARY...INCLUDING PORTIONS OF THE STL METRO AREA.

Mesoscale Discussion #0960


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 371 CONTINUES.

   

...THREAT INCREASING FOR DISCRETE SUPERCELLS CAPABLE OF PRODUCING LONG-TRACK/STRONG TORNADOES ACROSS WW 371...

   

INITIAL DISCRETE SUPERCELL THAT PROGRESSED ACROSS SHARP COUNTY AR HAS RECENTLY SHIFTED INTO SERN MO. ADDITIONAL DISCRETE CELLS ARE FORMING SW OF THIS TSTM WITHIN A CONFLUENCE AXIS THAT STRETCHED TOWARDS TXK. ENVIRONMENT ACROSS CNTRL/ERN AR IS EXTREMELY CONDUCIVE TO RAPID SUPERCELL EVOLUTION. MODIFIED 18Z LZK RAOB SUGGESTS MLCAPE HAS NOW REACHED 3500 TO 4000 J/KG WITH 0-1 KM SHEAR AROUND 30 KT. LARGE HODOGRAPHS...STRONG INSTABILITY AND A DISCRETE CONVECTIVE MODE WILL ALL REMAIN HIGHLY FAVORABLE FOR LONG-TRACKED SUPERCELLS PRODUCING STRONG TORNADOES AND VERY LARGE HAIL.

Mesoscale Discussion #0967


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 371 CONTINUES.

   

A THREAT OF LONG-TRACKED...STRONG TORNADOES IS PERSISTING OVER PORTIONS OF ERN AR...PROGRESSING ENEWD INTO WRN TN AND NRN MS...WHILE RIGHT-SPLITS WILL PROGRESS DUE EAST.

   

A SERIES OF DISCRETE SUPERCELLS ARE PERSISTING AHEAD OF AN EFFECTIVE DRYLINE/FRONTAL MERGER EXTENDING FROM A SURFACE LOW IN NERN MO...SWD THROUGH ERN AR...AND SWWD THROUGH TX. GIVEN THE EXPANSIVE WARM SECTOR CHARACTERIZED BY MID TO UPPER 80S TEMPERATURES IN CONJUNCTION WITH UPPER 60S DEW POINTS...THE ORIENTATION OF A STRONG SLY LOW LEVEL JET /50 KTS AT 1 KFT AT MEMPHIS VAD/ PERSISTING AFTER SUNSET WILL MAINTAIN AN INFLUX OF HIGHER THETA-E AIR. THIS WILL ALLOW DANGEROUS STORMS TO CONTINUE. DEEP LAYER SHEAR VECTORS ORTHOGONAL TO THE AFOREMENTIONED SURFACE BOUNDARIES AND SUBSTANTIALLY VEERING WINDS WITH HEIGHT WILL REMAIN CONDUCIVE TO DISCRETE SUPERCELLS CAPABLE OF PRODUCING LONG-TRACKED/STRONG TORNADOES.

Mesoscale Discussion #0968


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 370 CONTINUES.

   

THE THREAT FOR STRONG TORNADOES AND DAMAGING WINDS PERSISTS ACROSS THE ENTIRE AREA.

   

RADAR TRENDS INDICATE STORMS BEGINNING TO CONGEAL INTO A LINEAR MCS FROM S CNTRL IL INTO ERN MO. HOWEVER...NUMEROUS SUPERCELLS EXIST AHEAD OF THIS LINE...AND WILL HAVE THE GREATEST POTENTIAL TO PRODUCE TORNADOES. ADDITIONAL CELLS MAY DEVELOP AT ANY TIME AHEAD OF THE LINE AS THE WARM SECTOR IS UNCAPPED WITH UPPER 60S F DEWPOINTS.

   

EVEN IF THE LINEAR MCS OVERTAKES SUPERCELLS AHEAD OF IT...PARTICULARLY DAMAGING WINDS...POSSIBLY WIDESPREAD...MAY OCCUR ALONG WITH EMBEDDED TORNADOES AT TIMES.

Mesoscale Discussion #0979


CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

   

VALID 261555Z - 261730Z

   

STRONG BOUNDARY LAYER HEATING IS OCCURRING OVER MUCH OF PA AND NY WELL AHEAD OF PRIMARY FORCING ASSOCIATED WITH UPPER TROUGH OVER THE OH VALLEY.  IN THE ABSENCE OF SIGNIFICANT CLOUD COVER IT APPEARS VERY STEEP LOW LEVEL LAPSE RATES WILL SOON CONTRIBUTE TO DEEP BOUNDARY LAYER THERMALS AND WITH TIME A MATURING CU FIELD THAT SHOULD LEAD TO SCATTERED THUNDERSTORM DEVELOPMENT...ESPECIALLY OVER THE HIGHER TERRAIN FROM CNTRL PA INTO UPSTATE NY.  ADDITIONALLY...DEEP LAYER SHEAR PROFILES FAVOR SUPERCELL DEVELOPMENT AND LOW LEVEL MOISTURE IS SUCH THAT ISOLATED TORNADOES MAY ACCOMPANY THE MORE ORGANIZED CELLS.  VERY LARGE HAIL MAY ALSO BE NOTED GIVEN THE INSTABILITY OBSERVED.  THIS ENVIRONMENT IS BECOMING INCREASINGLY FAVORABLE FOR SEVERE DEVELOPMENT AND A TORNADO WATCH MAY BE ISSUED BY 18Z.

Mesoscale Discussion #0988


CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   

VALID 262218Z - 262315Z

   

A LOCALIZED SEVERE THREAT MAY PERSIST FOR A FEW MORE HOURS OVER SERN LA INTO SRN MS...BUT A WATCH IS LIKELY NOT NEEDED.

   

SMALL CLUSTER OF THUNDERSTORMS CONTINUES OVER THE AREA WHERE THE AIR MASS HAS BECOME VERY UNSTABLE WITH DEWPOINTS INTO THE LOWER 70S F. SWLY SURFACE FLOW VEERING TO NWLY IS CREATING FAVORABLE WIND PROFILES TO SUSTAIN A FEW SUPERCELLS GIVEN THE AMOUNT OF INSTABILITY IN PLACE.  

   

AMPLE LOW LEVEL CAPE EXISTS ALONG WITH 50-100 M2/S2 0-1 KM SRH...SUFFICIENT FOR BRIEF TORNADOES. DEGREE OF BOUNDARY LAYER MOISTURE MAY KEEP CIN AT A MINIMUM FOR SEVERAL MORE HOURS.


**This MCD preceded the Bush, Louisiana EF3 tornado

Mesoscale Discussion #1053


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 411...413...CONTINUES.

   

A THREAT FOR TORNADOES...LARGE HAIL AND WIND DAMAGE WILL CONTINUE ACROSS TORNADO WATCH 411 AND 413 THIS AFTERNOON INTO THE EARLY EVENING.

   

SEVERAL WELL-DEVELOPED SUPERCELLS ARE ONGOING FROM NRN MAINE SWD ACROSS THE WRN PART OF MAINE ALONG AN AXIS OF STRONG INSTABILITY. THIS AREA IS LOCATED TO THE EXIT REGION OF THE MID-LEVEL JET IN AN AREA WITH STRONG LOW-LEVEL SHEAR. THE WSR-88D VWP AT PORTLAND MAINE HAS A 0-3 KM STORM RELATIVE HELICITY OF 350 TO 400 M2/S2. THIS IS CREATING A FAVORABLE ENVIRONMENT FOR SUPERCELLS WITH WELL-DEVELOPED LOW-LEVEL MESOCYCLONES. AS THE SUPERCELLS MOVE ACROSS THE STRONGLY UNSTABLE AIRMASS IN CNTRL MAINE...TORNADOES...WIND DAMAGE AND LARGE HAIL WILL BE POSSIBLE WITH THE MORE INTENSE STORMS.

   

FURTHER TO THE SOUTH...SEVERAL VERY INTENSE STORMS ARE ONGOING ACROSS MA AND NRN CT. THIS ACTIVITY IS LOCATED JUST TO THE NORTHEAST OF A MAX OF STRONG INSTABILITY WITH MESOANALYSIS SHOWING MLCAPE VALUES IN THE 3000 TO 4000 J/KG. THIS ALONG WITH 45 TO 50 KT OF DEEP LAYER SHEAR WILL SUPPORT WELL-DEVELOPED SUPERCELLS WITH A THREAT OF TORNADOES AND LARGE HAIL. WIND DAMAGE WILL ALSO BE LIKELY ESPECIALLY IF SEVERAL OF THE STORMS CAN ORGANIZE INTO A LINE.


**This MCD preceded the Springfield, MA EF3 tornado

Mesoscale Discussion #1316


CONCERNING...OUTLOOK UPGRADE 

   

VALID 201542Z - 201645Z

   

CATEGORICAL MODERATE RISK...DRIVEN BY POTENTIALLY SIGNIFICANT HAIL/WIND AND PERHAPS TORNADOES...WILL BE EXPANDED TO INCORPORATE MUCH OF EASTERN KS AND CENTRAL/EASTERN PORTIONS OF OK /ROUGHLY OKC METRO AND I-40 NORTH/. FOR ADDITIONAL DETAILS...SEE THE FORTHCOMING DAY 1 OUTLOOK UPDATE WHICH WILL BE ISSUED BY 1630Z.

Mesoscale Discussion #1322


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 523 CONTINUES.

   

PARTICULARLY DANGEROUS TORNADO WATCH 523 CONTINUES UNTIL 01Z...WITH AN APPRECIABLE TORNADO RISK EXPECTED TO PERSIST/INCREASE ESPECIALLY FROM FAR NORTHERN KS INTO SOUTH-CENTRAL NEB THROUGH MID/LATE AFTERNOON.

   

AN IMPRESSIVE SUPERCELL WITH A HISTORY OF TORNADOES IS ONGOING IN NORTHWEST KS JUST NORTH OF THE HILL CITY AREA AS OF 1915Z...WITH A LIKELY REAR FLANK DOWNDRAFT INDUCED GUST ALSO NOTED PER A RECENT 46 KT WESTERLY GUST AT HLC. AS A 991 MB ANALYZED SURFACE LOW ACROSS NORTHERN KS CONTINUES TO SPREAD NORTH-NORTHEASTWARD...A VERY TORNADO CONDUCIVE ENVIRONMENT WILL REMAIN IMMEDIATELY NEAR/JUST NORTH OF THE SURFACE LOW AND IN VICINITY A SSW-NNE ORIENTED SURFACE BOUNDARY THAT EXTENDS ACROSS SOUTH-CENTRAL/EAST-CENTRAL NEB AND A NEIGHBORING WEST-EAST WARM FRONT THAT CONTINUES TO SHIFT EASTWARD INTO EASTERN NEB. 

   

IT IS ENTIRELY POSSIBLE THAT THIS SUPERCELL...AND PERHAPS OTHER SURFACE BASED VIGOROUS/SUPERCELLULAR DEVELOPMENT...WILL POSE AN APPRECIABLE TORNADO THREAT INTO SOUTH-CENTRAL NEB FROM 20-22Z AND BEYOND. THE AFOREMENTIONED SUPERCELL COULD IMPACT AREAS NEAR/EAST OF HOLDREGE AND KEARNEY...AND NEAR/WEST OF HASTINGS INCLUDING THE MINDEN AREA BY LATE THIS AFTERNOON. THIS IS A VERY DANGEROUS SITUATION. ASIDE FROM POSSIBLE TORNADOES...LARGE HAIL WILL BE A CONCERN.

Mesoscale Discussion #1325


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 523 CONTINUES.

   

PARTICULARLY DANGEROUS SITUATION TORNADO WATCH 523 CONTINUES UNTIL 01Z WITH A CONTINUED THREAT OF TORNADOES AND LARGE HAIL ESPECIALLY ACROSS SOUTH-CENTRAL/EAST-CENTRAL NEB INCLUDING THE I-80 CORRIDOR/CENTRAL NEB TRI-CITIES AREA THROUGH LATE AFTERNOON.

   

LATEST SUBJECTIVE SURFACE ANALYSIS CONTINUES TO REFLECT A NORTH-NORTHEASTWARD SHIFTING SURFACE LOW /AROUND 992 MB/ NOW LOCATED NEAR THE SOUTH-CENTRAL NEB/NORTH-CENTRAL KS BORDER. ON THE PERIPHERY OF THE SURFACE LOW...A WARM FRONT CONTINUES TO LIFT NORTHWARD ACROSS EASTERN NEB...WITH A SURFACE FRONT/FRONTAL BOUNDARY EXTENDING NORTHWARD FROM THE SURFACE LOW ACROSS CENTRAL NEB. THIS LATTER SSW-NNE ORIENTED BOUNDARY AND THE AREA ON THE IMMEDIATE NORTH SIDE OF THE SURFACE LOW WILL REMAIN HIGHLY FAVORABLE FOR TORNADOES INCLUDING THE I-80 CORRIDOR NEAR/EAST OF LEXINGTON TO KEARNEY TO GRAND ISLAND. HERE...RICH BOUNDARY LAYER MOISTURE CONTINUES TO WRAP WESTWARD NEAR/NORTH OF THE LOW AMID A HIGHLY SHEARED ENVIRONMENT. WITH TOWERING CU ALSO NOW NOTED NORTHEAST OF THE SURFACE LOW/NEAR THE WARM FRONT...EXPECT ADDITIONAL DEEP CONVECTIVE/SUPERCELLULAR DEVELOPMENT TO OCCUR FARTHER EAST ALONG THE I-80 GENERAL VICINITY/TRI-CITIES EAST-NORTHEASTWARD INTO EAST-CENTRAL NEB WHERE A VERY VOLATILE/WEAKLY INHIBITED BOUNDARY LAYER NOW EXISTS WITH 4000 J/KG OF MLCAPE.

Mesoscale Discussion #1329


THE SEVERE WEATHER THREAT FOR TORNADO WATCH 523...524...CONTINUES.

   

NEW WW WILL LIKELY BE FORTHCOMING TO REPLACE PARTS OF WW 523/524 AND TO INCLUDE PORTIONS OF SERN SD/NWRN IA.

   

GREATEST TORNADO THREAT SHOULD PERSIST ACROSS PORTIONS OF CNTRL/E-CNTRL NEB N/E OF PRIMARY SURFACE CYCLONE NEAR GRI...EVOLVING E/NEWD THROUGH THE NEXT FEW HOURS. ENLARGED HODOGRAPHS /SAMPLED BY OMAHA VWP/ HAVE CONTRIBUTED TO 0-1 KM SRH AOA 200 M2/S2 AMIDST A STRONGLY UNSTABLE AIR MASS WILL REMAIN VERY FAVORABLE FOR SUPERCELLS AND POTENTIAL SIGNIFICANT TORNADOES.

   

FARTHER SW...TSTM CLUSTER HAS REMAINED QUASI-STATIONARY INVOF PIVOT POINT OF SHORT WAVE TROUGH AXIS OVER NWRN KS. TORNADO THREAT SHOULD GRADUALLY DIMINISH HERE AS SHORT WAVE TROUGH CONTINUES EWD.

   

STRONG LINEAR FORCING ASSOCIATED WITH THE N/S-ORIENTED SURFACE COLD FRONT AND S/SWLY DEEP-LAYER FLOW HAVE RESULTED IN VIGOROUS UPSCALE GROWTH AND INCIPIENT QLCS FORMATION ACROSS PORTIONS CNTRL/ERN KS. AS MID-LEVEL SPEED MAX SHIFTS E/NEWD THIS EVENING AND SURFACE COLD POOL STRENGTHENS...EMBEDDED LEWPS/BOWING STRUCTURES APPEAR LIKELY TO DEVELOP...ENHANCING THE THREAT FOR DAMAGING WINDS ACROSS ERN KS/FAR SERN NEB TOWARDS THE MO RIVER VALLEY.

Mesoscale Discussion #1571


THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 623...624...CONTINUES.

   

ADDITIONAL WW ISSUANCE(S) MAY BE NEEDED E OF CURRENT WWS FROM LOWER MI TO NRN IL.  TWO PRIMARY MCS CLUSTERS AFFECT WW...

   

1. MOST SIGNIFICANT THREAT WILL REMAIN DOWNSHEAR FROM SIGNIFICANT-WIND PRODUCING COMPLEX MOVING EWD TO ENEWD 50-55 KT OVER ERN IA.  MOST INTENSE PORTION OF THIS COMPLEX YIELDED ESTIMATES OF 61-87 KT GUSTS OVER TAMA COUNTY IA AT 922Z... MEASURED 70 KT IN MARSHALL COUNTY AT 920Z...AND MEASURED 65 KT IN BENTON COUNTY IA AT 949Z.  THESE WERE ONLY SLIGHTLY BELOW MID-RANGE OF VALUES NOTED IN BASE VELOCITY OUTPUT FROM 500-3000 FT AGL...AS ACTIVITY RETREATED NEWD AWAY FROM DMX RADAR UNIT.  OUTFLOW BOUNDARY FROM WI COMPLEX WILL ACT AS PRIMARY FOCUS FOR FORWARD PROPAGATION AND LIFT ASSOCIATED WITH THIS MCS...HELPING TO CHANNEL THREAT FOR SVR GUSTS TOWARD DBQ AREA AND WI/IL BORDER REGION.  PROSPECTIVE INFLOW-LAYER AIR MASS S OF OUTFLOW BOUNDARY WILL REMAIN RICHLY MOIST WITH SFC DEW POINTS 70S F...AMIDST 35-45 KT EFFECTIVE SHEAR VECTORS ALIGNED ORTHOGONALLY WITH RESPECT TO CONVECTIVE BAND.  STRENGTHENING CINH AND WEAKENING SHEAR WITH SWD EXTENT OVER NRN IL LEND MORE CONDITIONAL/UNCERTAIN THREAT S OF I-80 CORRIDOR...HOWEVER SVR TSTM WINDS MAY AFFECT DBQ/RFD/CHI AREAS IN THAT ORDER THROUGH MID-LATE MORNING.

   

2. SQUALL LINE FROM GRB-MSN AS OF 930Z..MOVING ESEWD 40-45 KT TOWARD WRN/CENTRAL LM AND EVENTUALLY PORTIONS WRN LOWER MI.  CONVECTION CONTINUES TO MOVE EWD ALONG LOW-LEVEL BAROCLINIC ZONE AND RELATED THETAE GRADIENT...WITH POTENTIAL FOR OCNL DAMAGING GUSTS.  THIS ACTIVITY HAS PRODUCED A FEW DAMAGING GUSTS...INCLUDING ONE MEASURED SVR GUST OF 55 KT IN GREEN LAKE COUNTY WI AT 905Z.  POTENTIAL FOR INTERMITTENT WIND DAMAGE WILL CONTINUE WITH THIS ACTIVITY AS IT MOVES ACROSS LAKESHORE.  AIR MASS IS NEITHER AS UNSTABLE NOR AS CHARACTERIZED BY FAVORABLE DEEP-LAYER SHEAR E OF LM AS OVER WI.  HOWEVER...PRESENCE OF MATURE COLD POOL WITH FORWARD-PROPAGATIONAL SLAB OF ASCENT...ALONG WITH FAVORABLE LOW-LEVEL WAA/MOISTURE TRANSPORT JUST ABOVE SFC...SUGGEST COMPLEX MAY OFFER RISK OF WIND DAMAGE OVER PORTIONS LOWER MI AS WELL.  WW MAY BE REQUIRED THERE.

Mesoscale Discussion #1573


CONCERNING...OUTLOOK UPGRADE 

   

VALID 111250Z - 111345Z

   

13Z SPC DAY-1 OUTLOOK WILL INCLUDE UPGRADED TSTM WIND PROBABILITIES SUPPORTING CATEGORICAL MDT RISK ROUGHLY OVER OUTLINED REGION...GIVEN EXPECTED DESTABILIZATION/MOISTENING OF AIR MASS TODAY AND POTENTIAL FOR ONE OR MORE DAMAGING WIND-PRODUCING MESOSCALE CONVECTIVE SYSTEMS.  REF 13Z SVR OUTLOOK FOR DETAILS.

Mesoscale Discussion #1644


CONCERNING...TORNADO WATCH 652...

   

VALID 172334Z - 180030Z

   

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 652 CONTINUES.

   

ISOLATED LONG-LIVED TORNADIC SUPERCELL...LOCATED OVER LAMOURE COUNTY ND...IS PROPAGATING SSEWD AT ROUGHLY 20KT.  THIS STORM IS A BIT DEVIANT TO FORECAST STORM MOTION AND BASED ON CURRENT SPEED/MOVEMENT SHOULD SPREAD ACROSS DICKEY COUNTY ND INTO BROWN/MARSHALL COUNTY SD BEFORE 01Z.  THIS MAY NECESSITATE A NEW TORNADO WATCH OVER NERN SD AS ENVIRONMENTAL CONDITIONS ARE QUITE UNSTABLE AND MORE THAN ADEQUATELY SHEARED FOR SUPERCELLS/TORNADOES.


**This MCD was released as the Berlin, North Dakota EF3 tornado was ongoing