DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 251251
SWODY1
SPC AC 251249

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 AM CDT WED APR 25 2012

VALID 251300Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON INTO
TONIGHT ACROSS PORTIONS OF THE MIDWEST AND OH VALLEY INTO CNTRL
APPALACHIANS...

...SYNOPSIS...

100+ KT MIDLEVEL JET STREAK CENTERED NEAR 41N/143W WILL DEVELOP SEWD
TOWARD THE NRN CA COAST...SUPPORTING THE OPENING AND SUBSEQUENT EWD
PROGRESSION OF UPPER LOW FROM VICINITY OF 30N/128W INTO THE LOWER CO
VALLEY BY 26/12Z. THIS PATTERN EVOLUTION COUPLED WITH THE SEWD
MOVEMENT OF A SHORTWAVE TROUGH FROM NRN MANITOBA INTO THE UPPER
GREAT LAKES WILL CONTRIBUTE TO THE AMPLIFICATION AND EWD DEVELOPMENT
OF MIDLEVEL RIDGE FROM THE INTER-MOUNTAIN WEST INTO THE HIGH
PLAINS.

AT THE SURFACE...LOW PRESSURE OVER SWRN MN WILL DEVELOP SEWD TO
VICINITY OF THE QUAD CITIES BY 26/00Z BEFORE ACCELERATING INTO CNTRL
OH BY THE END OF THE D1 PERIOD. THIS MIGRATORY CYCLONE WILL TRACK
ALONG A WARM FRONT WHICH WILL DEVELOP EWD ACROSS THE OH VALLEY
WITHIN A PERSISTENT LOW-LEVEL WAA REGIME. THE AREA OF LOW PRESSURE
WILL BE TRAILED BY A COLD FRONT WHICH WILL ADVANCE SWD FROM THE NRN
PLAINS AND UPPER MS VALLEY. A PRE-FRONTAL TROUGH IS FORECAST TO
STRENGTHEN TODAY...EXTENDING FROM THE SURFACE LOW SWWD THROUGH NWRN
MO TO S-CNTRL KS WHERE IT WILL LINK WITH A DRYLINE STRETCHING SWD
THROUGH WRN OK INTO W-CNTRL TX.

...MIDWEST/OH VALLEY INTO CNTRL APPALACHIANS THIS AFTERNOON AND
TONIGHT...

RECENT OBSERVATIONAL DATA AND NUMERICAL GUIDANCE HAVE BRED
INCREASING UNCERTAINTY IN THE CONVECTIVE FORECAST LATER TODAY INTO
TONIGHT. MOISTURE QUALITY REMAINS PROBLEMATIC WITH 12Z REGIONAL
SOUNDINGS SHOWING LOWEST 100-MB MEAN-MIXING RATIOS OF ONLY 6-9 G/KG.
THIS COUPLED WITH INCREASING MID AND HIGH-LEVEL CLOUDINESS MAY
IMPACT THE DEGREE OF INSTABILITY THAT DEVELOPS TODAY.
FINALLY...THERE IS SOME INDICATION THAT FORCING ASSOCIATED WITH AN
UPSTREAM IMPULSE MAY MOVE ACROSS THE REGION FAIRLY EARLY
TODAY...PRIOR TO ENVIRONMENT SUFFICIENTLY DESTABILIZING.

BASED ON AN ARRAY OF MODEL SOLUTIONS...THE CORRIDOR FROM E-CNTRL IL
ACROSS CNTRL/SRN IND INTO SWRN OH AND N-CNTRL KY APPEARS TO HAVE THE
HIGHEST LIKELIHOOD OF EXPERIENCING SEVERE WEATHER FROM LATE THIS
AFTERNOON INTO TONIGHT. THIS REGION WILL RESIDE ON THE ERN FRINGE
OF STRONGER CAP ASSOCIATED WITH THE EML WHERE INCREASING BOUNDARY
LAYER MOISTURE AND THE STEEP MIDLEVEL LAPSE RATES WILL YIELD MLCAPE
VALUES RANGING FROM AROUND 1000 J/KG INVOF WARM FRONT TO POTENTIALLY
AS HIGH AS 2000-3000 J/KG OVER WRN IL. THIS INSTABILITY WILL
COINCIDE WITH A KINEMATIC ENVIRONMENT FEATURING A VERTICALLY VEERING
WIND PROFILE /ESPECIALLY ALONG WARM FRONT/ AND 40-50 KT OF DEEP NWLY
SHEAR.

INITIAL STORM MODE WILL LIKELY BE SUPERCELLULAR WITH AN ATTENDANT
RISK FOR LARGE-HAIL...DAMAGING WINDS...AND PERHAPS A TORNADO OR TWO.
THEREAFTER...A NUMBER OF CONVECTION-ALLOWING MODEL SOLUTIONS
INDICATE POTENTIAL UPSCALE GROWTH INTO A BOWING MCS. SHOULD THIS
SCENARIO UNFOLD...THE THREAT FOR DAMAGING WINDS AND HAIL WILL
CONTINUE INTO TONIGHT PERHAPS AS FAR E AS THE CNTRL APPALACHIANS.

...OZARKS...

THE MAJORITY OF MODEL GUIDANCE SUGGESTS THAT THE AIR MASS ACROSS
REGION WILL REMAIN CAPPED TO SURFACE-BASED TSTM DEVELOPMENT.
HOWEVER...OUTLIER SOLUTIONS DO INDICATE THE POTENTIAL FOR ISOLATED
TSTM DEVELOPMENT LATE THIS AFTERNOON AND EVENING ALONG PRE-FRONTAL
TROUGH WHICH WILL TRAIL OH VALLEY SURFACE LOW. INSPECTION OF
FORECAST SOUNDINGS SUGGEST THAT STRONG DAYTIME HEATING AND
CONVERGENCE ALONG THIS BOUNDARY MAY BE SUFFICIENT FOR STORM
INITIATION. ASSUMING A STORM CAN BECOME SUSTAINED...THE COMBINATION
OF MODERATE-STRONG INSTABILITY AND MODEST DEEP-LAYER SHEAR SUGGEST A
RISK FOR SEVERE WEATHER. AS SUCH...LOW PROBABILITIES HAVE BEEN
INCLUDED FOR THIS REGION.

...NRN ROCKIES...

LATEST MODEL GUIDANCE SUGGESTS THAT A WEAK MIDLEVEL IMPULSE EMBEDDED
WITHIN SUBTROPICAL MOISTURE PLUME OVER THE SRN SIERRA-NEVADAS WILL
APPROACH THE REGION LATER TODAY. FORCING ASSOCIATED WITH THIS
FEATURE WILL AUGMENT DAYTIME HEATING ALONG THE HIGH TERRAIN TO GIVE
RISE TO ISOLATED-WIDELY SCATTERED TSTMS LATE THIS AFTERNOON AND
EVENING. SIMILAR TO PREVIOUS DAYS...THE PRESENCE OF STEEP LAPSE
RATES...PW VALUES OF 0.5-0.8 INCH AND 40-45 KT OF DEEP-LAYER SHEAR
WILL SUPPORT A FEW STRONG-MARGINALLY SEVERE STORMS CAPABLE OF HAIL
AND STRONG WIND GUSTS.

..MEAD/LEITMAN.. 04/25/2012

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