Archive for March, 2012

Mesoscale discussion #0391 for S-CNTRL TX, severe thunderstorm watch possible!

New mesoscale discussion is out for N-CNTRL TX, concerning severe potential for a few isolated storms along the dryline there… watch possible.

MESOSCALE DISCUSSION 0391
NWS STORM PREDICTION CENTER NORMAN OK
0459 PM CDT FRI MAR 30 2012

AREAS AFFECTED…CNTRL/NW TX

CONCERNING…SEVERE POTENTIAL…WATCH POSSIBLE

VALID 302159Z – 302300Z

A THREAT FOR LARGE HAIL AND ISOLATED DMGG WIND GUSTS MAY DEVELOP WITHIN THE NEXT 1-2 HRS OVER PORTIONS OF CNTRL TX. TSTM COVERAGE REMAINS SOMEWHAT UNCERTAIN…BUT CONVECTIVE TRENDS ARE BEING MONITORED FOR A POSSIBLE WW.

TOWERING CU FIELD HAS BECOME MORE AGITATED IN RECENT VISIBLE SATELLITE IMAGES E OF JCT…FORMING ALONG/NEAR A WEAKLY CONFLUENT/DIFFUSE DRYLINE. STRONG DAYTIME HEATING HAS LIKELY RESULTED IN EROSION OF MOST CINH…AND AS WEAK FORCED ASCENT ACCOMPANYING AN UPPER IMPULSE /NOTED IN WATER VAPOR IMAGERY OVER NW
TX/ OVERSPREADS THE AREA…DEVELOPMENT OF A FEW TSTMS SHOULD BECOME MORE PROBABLE PRIOR TO SUNSET. WITH MODEST MIDLEVEL WLY FLOW /E.G. 15-20 KTS AT 6 KM AGL PER LDB PROFILER/…STORMS SHOULD SLOWLY PROGRESS E-SEWD INTO A MORE MOIST/UNSTABLE ENVIRONMENT…WITH MODIFIED FORECAST SOUNDINGS SHOWING MLCAPE VALUES EXCEEDING 3000 J/KG. PRIMARY THREAT WITH THESE TSTMS APPEARS TO BE HAIL /SOME VERY LARGE/…AS WELL AS ISOLATED DMGG WIND GUSTS GIVEN A HOT/WELL-MIXED BOUNDARY LAYER. ONE FACTOR PRECLUDING A MORE SIGNIFICANT/WIDESPREAD THREAT WILL BE WEAK DEEP-LAYER SHEAR LIMITING STORM ORGANIZATION…FAVORING PULSE TO MULTICELL CONVECTIVE MODES. THIS…COMBINED WITH EXPECTED SPARSE COVERAGE OF CONVECTION…WILL LEAD TO UNCERTAINTY WHETHER A WW WILL BE REQUIRED…BUT TRENDS WILL CONTINUE TO BE MONITORED OVER THE NEXT 1-2 HRS.

..ROGERS.. 03/30/2012

Another mesoscale discussion is out also for E NE/W IA concerning potential for a few isolated severe storms there… watch is unlikely.

MESOSCALE DISCUSSION 0390
NWS STORM PREDICTION CENTER NORMAN OK
0320 PM CDT FRI MAR 30 2012

AREAS AFFECTED…ERN NEB…WRN IA

CONCERNING…SEVERE POTENTIAL…WATCH UNLIKELY

VALID 302020Z – 302145Z

ISOLATED THUNDERSTORMS ARE FORECAST TO DEVELOP ACROSS ERN NEB AND WRN IA THIS AFTERNOON AND EVENING. A SVR STORM WILL BE POSSIBLE…BUT THE THREAT IS TOO MARGINAL FOR A WW.

MESOANALYSIS AT 19-20Z SHOWS A BAROCLINIC ZONE COLLOCATED WITH CONFLUENT SURFACE STREAMLINES EXTENDING SEWD OUT OF SRN SD TOWARD OMA AND INTO NRN MO. MEANWHILE…A MIDLEVEL IMPULSE IS MOVING SEWD TOWARD ERN NEB/WRN IA. STEEP LOW-LEVEL LAPSE RATES INDICATIVE OF ROBUST BOUNDARY LAYER DESTABILIZATION ARE DEVELOPING EWD TOWARD THE SURFACE BOUNDARY. THIS DESTABILIZATION COMBINED WITH ASCENT ASSOCIATED WITH THE MIDLEVEL IMPULSE APPEAR TO BE AIDING IN SURFACE BASED CUMULUS DEVELOPMENT INVOF BUB AND ONL…WHICH MAY DEEPEN/EVOLVE INTO ISOLATED THUNDERSTORMS AS RELATIVELY DEEPER MOISTER IS ENCOUNTERED OVER ERN NEB. COMBINATION OF STEEP MIDLEVEL LAPSE RATES FROM 7-8 C/KM…SURFACE TEMPERATURES IN THE MID 70S AND DEWPOINTS IN THE 40S TO LOW 50S WILL AID IN MLCAPE VALUES NEAR 500 J/KG. GIVEN THE PRESENCE OF LOW-LEVEL SWLYS VEERING TO W-NWLY IN THE MIDLEVELS…VERTICAL SHEAR PROFILES…CHARACTERIZED BY 0-6 KM BULK WIND DIFFERENCE FROM 30-50 KT…WILL SUPPORT ORGANIZED THUNDERSTORM DEVELOPMENT INCLUDING SUPERCELLS. THESE STORMS WILL BE DRIVEN SEWD ALONG THE BAROCLINIC ZONE COINCIDENT WITH THE PASSAGE OF THE MIDLEVEL IMPULSE…AND POSE A THREAT FOR ISOLATED DAMAGING WIND GUSTS AND LARGE HAIL. HOWEVER…GIVEN ONLY MARGINAL MOISTURE AND BUOYANCY…THE SVR THREAT SHOULD BE NARROWLY CONFINED TO THE BAROCLINIC ZONE…AND BE TOO LIMITED FOR A WW.

..GARNER.. 03/30/2012

Stay tuned!


Severe storms with large hail and severe winds for S Plains and OH valley today!

Two areas for severe storms today, one across IL/IN/OH along the frontal system and another across N TX/S OK ahead of a dryline. SPC has issued a ASLGT riask for both areas with 15% hatched area for very large hail over S Plains and 30% for large hail over OH valley…

AY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT FRI MAR 30 2012

VALID 301630Z – 311200Z

…THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT OVER MUCH OF THE OH VALLEY…

…THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT ACROSS PARTS OF THE SRN PLAINS…

…SYNOPSIS…

MORNING WATER VAPOR IMAGERY SHOWS A NUMBER OF VORTICITY MAXIMA EMBEDDED WITHIN QUASI-ZONAL FLOW REGIME E OF THE ROCKIES. ONE SUCH FEATURE –OF CONVECTIVE ORIGIN– OVER SRN LAKE MI INTO LOWER MI WILL WEAKEN WHILE MOVING INTO A CONFLUENT REGION ACROSS THE LOWER GREAT LAKES. UPSTREAM FROM THIS FEATURE…A VORTICITY MAXIMUM OVER WRN SD/NWRN NEB WILL TRANSLATE SEWD INTO THE MID MS VALLEY BY 31/12Z. MEANWHILE…A PERTURBATION OVER THE LOWER MS VALLEY WILL PROGRESS
SLOWLY EWD ACROSS THE GULF COAST STATES.

IN THE LOW LEVELS…SURFACE CYCLONE OVER NRN IL WILL DEVELOP EWD ACROSS THE OH VALLEY TODAY IN TANDEM WITH THE INITIAL IMPULSE MENTIONED ABOVE. THIS SURFACE LOW WILL BE ATTENDED BY A COLD FRONT WHICH WILL SETTLE SWD TOWARD THE OH RIVER. ELSEWHERE…LOW PRESSURE OVER NWRN TX WILL DEVELOP SLOWLY SEWD IN RESPONSE TO STRONG DIABATIC HEATING OVER THE LOW ROLLING PLAINS AND W-CNTRL TX. A DRYLINE WILL BECOME BETTER-DEFINED BY AFTERNOON FROM THIS LOW SWD TO NEAR DRT.

…OH VALLEY…

SWLY LLJ OVER IL/IND WILL MIGRATE EWD TODAY IN CONJUNCTION WITH THE MIDLEVEL SYSTEM…ENHANCING THE FLUX OF A WARMER AND MORE MOIST BOUNDARY LAYER OBSERVED OVER CNTRL/SRN IL EWD ACROSS THE OH VALLEY. THIS PROCESS WILL COINCIDE WITH THE EWD ADVECTION OF AN EML LOBE SAMPLED BY THE 12Z ILX SOUNDING /I.E. MIDLEVEL LAPSE RATE OF 7.5-8.0 C PER KM/…CONTRIBUTING TO A MODERATELY UNSTABLE WARM SECTOR BY AFTERNOON WITH MLCAPE VALUES APPROACHING 1500-2500 J/KG.

THE MAJORITY OF ELEVATED TSTMS ONGOING ACROSS SRN LOWER MI/NRN IND WILL LIKELY REMAIN DISPLACED TO THE NE OF EVOLVING WARM SECTOR WITH SOME MARGINALLY SEVERE HAIL BEING THE PRIMARY HAZARD. BY EARLY/MID AFTERNOON…THE SWRN EXTENSION OF THESE STORMS MAY BECOME ROOTED WITHIN THE DESTABILIZING BOUNDARY LAYER OVER NRN IN/NWRN OH WITH SUBSEQUENT STORM DEVELOPMENT ANTICIPATED SWWD ALONG TRAILING COLD FRONT.

FORECAST HODOGRAPHS INVOF MIGRATORY SURFACE LOW INDICATE VERTICALLY VEERING WINDS WITH HEIGHT WITH 40-45 KT OF DEEP WLY SHEAR WHICH DECREASES WITH SWWD EXTENT ALONG TRAILING COLD FRONT. GIVEN THE MODERATE INSTABILITY…THE SETUP WILL SUPPORT A MIXTURE OF SUPERCELL…MULTICELL…AND BOWING STRUCTURES CAPABLE OF PRIMARILY SEVERE HAIL AND DAMAGING WIND GUSTS. A TORNADO OR TWO IS POSSIBLE…NAMELY WITH ANY SUPERCELLS THAT CAN BECOME ESTABLISHED NEAR THE SURFACE LOW WHERE LOW-LEVEL SHEAR IS MAXIMIZED. EXPECT THE SEVERE WEATHER THREAT TO DIMINISH LATER TONIGHT AS THE BOUNDARY LAYER BEGINS TO COOL AND STABILIZE.

…SRN PLAINS…

12Z REGIONAL SOUNDINGS SHOW THE CO-LOCATION OF A MOIST BOUNDARY LAYER /I.E. 100-MB LOWEST MEAN-MIXING RATIOS OF 10-14 G PER KG/ WITH STEEP MIDLEVEL LAPSE RATES ASSOCIATED WITH THE EML WHICH WILL CONTRIBUTE TO STRONG AFTERNOON INSTABILITY WITH MLCAPE VALUES APPROACHING 2500-4000 J/KG. HOWEVER…STORM INITIATION REMAINS IN QUESTION OWING TO THE ABSENCE OF ANY NOTABLE MIDLEVEL IMPULSES IN WATER VAPOR IMAGERY. CURRENTLY…IT APPEARS THAT THE HIGHEST PROBABILITY FOR TSTM DEVELOPMENT WILL BE FROM THE VICINITY OF THE SURFACE LOW OVER NWRN TX/SWRN OK SWD ALONG THE DRYLINE INTO W-CNTRL TX. HERE…DAYTIME HEATING AND LOW-LEVEL CONVERGENCE WILL LIKELY BE MAXIMIZED…POTENTIALLY ALLOWING FOR THE LOCAL ELIMINATION OF THE CAP.

GIVEN STORM DEVELOPMENT AND SUSTENANCE…THE STRONG INSTABILITY WILL COMPENSATE FOR THE MARGINAL VERTICAL SHEAR /I.E. EFFECTIVE BULK SHEAR OF AROUND 30 KT/…PROMOTING SUPERCELL DEVELOPMENT. THE PRIMARY HAZARD WILL BE VERY LARGE HAIL THROUGH THIS EVENING BEFORE STORMS WEAKEN WITH THE LOSS OF DAYTIME HEATING.

..MEAD/GARNER.. 03/30/2012

The mesoscale discussion was out awhile ago concerning severe potential for OH valley where SE-wards advancing cold front should soon initiate storms…

MESOSCALE DISCUSSION 0389
NWS STORM PREDICTION CENTER NORMAN OK
0112 PM CDT FRI MAR 30 2012

AREAS AFFECTED…WRN/CNTRL OH…CNTRL/SRN IND…SRN IL

CONCERNING…SEVERE POTENTIAL…WATCH LIKELY

VALID 301812Z – 301945Z

THUNDERSTORM DEVELOPMENT IS FORECAST TO TAKE PLACE DURING THE NEXT FEW HRS ACROSS PORTIONS OF WRN OH SWWD INTO CNTRL IND AND SRN IL. SVR STORMS WILL BE PROBABLE…AND A WW ISSUANCE WILL LIKELY BE NEEDED BY 19-20Z.

MIDDAY MESOANALYSIS PLACES AN AREA OF SURFACE LOW PRESSURE OVER NWRN IND AT 17Z…WHICH IS COINCIDENT WITH A MIDLEVEL IMPULSE MOVING E ACROSS LK MI. WARM SECTOR AIRMASS…CHARACTERIZED BY TEMPERATURES WARMING INTO THE MID TO UPR 70S WITH DEWPOINTS FROM THE MID 50S TO LOW 60S…IS BOUNDED BY A COLD FRONT EXTENDING SWWD INTO CNTRL/SRN MO…AND A WARM FRONT EXTENDING SEWD INTO ERN KY. STEEP MIDLEVEL LAPSE RATES NEAR 8 C/KM RESIDE ABOVE THE DESTABILIZING WARM SECTOR AIRMASS…AND WILL AID IN MLCAPE VALUES FROM 1000-1500 J/KG BY PEAK HEATING. MEANWHILE…AS THE AFTERNOON PROGRESSES…THE SURFACE LOW AND WARM FRONT WILL ADVANCE INTO OH…WHILE THE COLD FRONT DROPS S-SEWD TOWARD SRN IND AND IL. THE COMBINATION OF CONVERGENCE AND BOUNDARY LAYER DESTABILIZATION ALONG THE FRONT…AS WELL AS WEAK LARGE-SCALE ASCENT ASSOCIATED WITH THE PREVIOUSLY MENTIONED UPPER WAVE…SHOULD BE SUFFICIENT FOR THUNDERSTORM INITIATION ALONG THE COLD FRONT…PERHAPS AS EARLY AS 19-20Z BASED ON RECENT RUNS OF THE HRRR.

MIDLEVEL WLYS RANGE FROM 50 KT NEAR THE LK MI IMPULSE…TO 20-30 KT OVER SRN IL…AND WILL YIELD SUFFICIENTLY STRONG DEEP-LAYER VERTICAL WIND SHEAR /I.E. 0-6 KM BULK WIND DIFFERENCE FROM 20-40 KT/ FOR ORGANIZED MULTICELL AND SUPERCELL STORM DEVELOPMENT. GIVEN THE LINEAR NATURE OF LOW-LEVEL FORCING ALONG THE COLD FRONT…STORMS MAY TEND TO ORGANIZE INTO LINE SEGMENTS…AND WILL POSE A THREAT FOR DAMAGING WINDS AND LARGE HAIL. CLOSER TO THE SURFACE LOW AND WARM
FRONT OVER IND AND OH…SURFACE WINDS WILL BE MORE STRONGLY BACKED…WHICH WILL MAXIMIZE LOW-LEVEL VERTICAL WIND SHEAR /0-1 KM SRH AOA 150 M2 S-2/…AND INCREASE THE POTENTIAL FOR TORNADOES.

..GARNER.. 03/30/2012

Additionally, two SVR TSTORM watched have been already issued… one for S IN/S-CNTRL OH…

Tornadoes
Probability of 2 or more tornadoes Low (20%)
Probability of 1 or more strong (F2-F5) tornadoesLow (5%)

Wind
Probability of 10 or more severe wind eventsMod (30%)
Probability of 1 or more wind events > 65 knotsMod (30%)

Hail
Probability of 10 or more severe hail eventsMod (50%)
Probability of 1 or more hailstones > 2 inchesLow (20%)

Combined Severe Hail/Wind
Probability of 6 or more combined severe hail/wind eventsHigh (80%)

RGENT – IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 118
NWS STORM PREDICTION CENTER NORMAN OK
325 PM EDT FRI MAR 30 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

INDIANA
WESTERN OHIO

EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 325 PM UNTIL 1100 PM EDT.

HAIL TO 2 INCHES IN DIAMETER…THUNDERSTORM WIND GUSTS TO 70 MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

DISCUSSION…TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND INTENSITY THIS AFTERNOON INTO EVENING ALONG AND AHEAD OF COLD FRONT ADVANCING EWD/SEWD THROUGH THE REGION. WARM SECTOR AIR MASS HAS WARMED THROUGH THE 70S INTO LOWER 80S…AND WHEN COUPLED WITH DEWPOINTS IN THE 50S AND STEEP MIDLEVEL LAPSE RATES…ENVIRONMENT HAS BECOME MODERATELY UNSTABLE WITH SBCAPE OF 1000-2000 J/KG. THIS INSTABILITY IN CONJUNCTION WITH A BELT OF 50+ KT WLY FLOW ABOVE 3 KM AGL WILL SUPPORT ORGANIZED STORM MODES INCLUDING SUPERCELLS AND BOWING STRUCTURES CAPABLE OF MAINLY DAMAGING WINDS AND LARGE HAIL.

…MEAD

And another one for S IL…

Tornadoes
Probability of 2 or more tornadoes Low (20%)
Probability of 1 or more strong (F2-F5) tornadoesLow (5%)

Wind
Probability of 10 or more severe wind eventsMod (30%)
Probability of 1 or more wind events > 65 knotsMod (30%)

Hail
Probability of 10 or more severe hail eventsMod (30%)
Probability of 1 or more hailstones > 2 inchesLow (20%)

Combined Severe Hail/Wind
Probability of 6 or more combined severe hail/wind eventsHigh (70%)

URGENT – IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 119
NWS STORM PREDICTION CENTER NORMAN OK
255 PM CDT FRI MAR 30 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

SOUTHERN ILLINOIS
FAR SOUTHWEST INDIANA

EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 255 PM UNTIL 1000 PM CDT.

HAIL TO 1.5 INCHES IN DIAMETER…THUNDERSTORM WIND GUSTS TO 70 MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

OTHER WATCH INFORMATION…CONTINUE…WW 118…

DISCUSSION…TSTMS DEVELOPING ALONG COLD FRONT SHOULD CONTINUE TO INTENSIFY THIS AFTERNOON WHILE INTERACTING WITH A MOIST AND MODERATELY UNSTABLE WARM SECTOR WHERE SBCAPE HAS RISEN TO 1500-2500 J/KG. LARGE-SCALE FORCING FOR ASCENT AND VERTICAL SHEAR MAY TEND TO DIMINISH WITH TIME OWING TO THE EWD PROGRESSION OF MIDLEVEL IMPULSE AWAY FROM THE REGION. NONETHELESS…THE STEEP LOW TO MIDLEVEL LAPSE RATES AND MODERATE INSTABILITY WILL SUPPORT A RISK FOR SEVERE HAIL AND DAMAGING WINDS WITH THE STRONGEST STORMS.

…MEAD

Stay tuned!


SVR TSTORM watch #0116 for E-CNTRL KS into NW OK, storms rapidly firing along the DL!

Storms are rapidly forming along the dryline from CNTRL KS into NW OK as seen on the latest satellite and radar images…

A SVR TSTORM watch has been issued, storms will increase in coverage and intensity while spreading east in the next hours.

Tornadoes
Probability of 2 or more tornadoes Low (20%)
Probability of 1 or more strong (F2-F5) tornadoesLow (5%)

Wind
Probability of 10 or more severe wind eventsMod (30%)
Probability of 1 or more wind events > 65 knotsLow (20%)

Hail
Probability of 10 or more severe hail eventsMod (30%)
Probability of 1 or more hailstones > 2 inchesLow (20%)

Combined Severe Hail/Wind
Probability of 6 or more combined severe hail/wind eventsHigh (70%)

DISCUSSION…THUNDERSTORMS ARE EXPECTED TO INCREASE IN COVERAGE/INTENSITY ALONG A SURFACE DRYLINE IN NW OK…AND AS THE DRYLINE IS OVERTAKEN BY A COLD FRONT INTO CENTRAL KS. MODERATE INSTABILITY IS PRESENT IN ADVANCE OF THE BOUNDARIES…WHERE STRONG SURFACE HEATING AND FOCUSED LOW-LEVEL ASCENT ARE WEAKENING CONVECTIVE INHIBITION. DEEP-LAYER VERTICAL SHEAR IS ON THE LOWER MARGINS FOR SUSTAINED SUPERCELLS /PRIMARILY IN KS/…BUT THE MODERATE INSTABILITY/STEEP LAPSE RATES WILL SUPPORT A RISK FOR LARGE HAIL AND DAMAGING WINDS FOR THE NEXT SEVERAL HOURS. THE SEVERE THREAT SHOULD PEAK BY LATE EVENING…AND THEN DECREASE BY 02-03Z AS THE BOUNDARY LAYER BEGINS TO COOL AND THE CAP AGAIN STRENGTHENS.

Stay tuned!