SWODY1
SPC AC 301954
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT FRI MAR 30 2012
VALID 302000Z - 311200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE OH AND MID
MS VALLEYS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
PLAINS...
ONLY THREE CHANGES HAVE BEEN MADE TO THE OUTLOOK AT 20Z. THE FIRST
CHANGE IS TO EXTEND THE SLIGHT RISK AREA SWD ACROSS CNTRL TX ALONG
AND JUST EAST OF A DRYLINE. SHORT-TERM MODEL FORECASTS SUGGEST
ISOLATED CONVECTION MAY INITIATE ALONG AN AXIS OF STRONG
INSTABILITY. THE WIND SHEAR ENVIRONMENT WILL LIKELY SUPPORT
SUPERCELLS WITH LARGE HAIL WITH A CHANCE FOR HAIL GREATER THAN 2
INCHES IN DIAMETER DUE TO THE STRONG INSTABILITY AND STEEP LAPSE
RATES. THE SECOND CHANGE TO THE OUTLOOK IS TO ADD A 5 PERCENT WIND
DAMAGE AND HAIL PROBABILITY IN ERN NEB AND WRN IA WHERE SHORT-TERM
MODEL FORECASTS INITIATE THUNDERSTORMS. MESOANALYSIS SHOWS A NARROW
AXIS OF MODERATE INSTABILITY EXTENDING NNWWD ACROSS ERN NEB WITH
SBCAPE AROUND 1000 J/KG AND 0-6 KM SHEAR OF 45 TO 50 KT. THIS
ENVIRONMENT SHOULD AT LEAST SUPPORT A MARGINAL SEVERE THREAT LATE
THIS AFTERNOON. THE THIRD CHANGE IS TO REMOVE PART OF THE SLIGHT
RISK AREA IN ERN IL AND NW IND BEHIND A DEVELOPING LINE OF STORMS.
OTHERWISE...THE OUTLOOK LOOKS TO BE ON TRACK.
..BROYLES.. 03/30/2012
.PREV DISCUSSION... /ISSUED 1129 AM CDT FRI MAR 30 2012/
...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.
...CNTRL/ERN GULF COAST...
AS MENTIONED ABOVE...MIDLEVEL CIRCULATION OVER CNTRL MS AS OF 16Z
WILL TRACK EWD TODAY...FOSTERING SCATTERED TSTMS THIS AFTERNOON
WITHIN A MOIST AND MODERATELY UNSTABLE AIR MASS WITH MLCAPE OF
1000-1500 J/KG. WHILE VERTICAL SHEAR WILL BE GENERALLY WEAK...THE
12Z LIX SOUNDING DID SAMPLE A BELT OF 35-40 KT FLOW IN THE MIDLEVELS
WHICH WILL POTENTIALLY ENHANCE STORM ORGANIZATION ALONG THE GULF
COAST TODAY. LOCALLY DAMAGING WIND GUSTS APPEAR TO BE THE PRIMARY
HAZARD OWING TO WATER LOADING EFFECTS...THOUGH A BRIEF TORNADO
CANNOT BE RULED OUT.
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