DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 291254
SWODY1
SPC AC 291252

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0752 AM CDT TUE MAY 29 2012

VALID 291300Z - 301200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT
FROM THE UPPER OH VALLEY EWD INTO NEW ENGLAND AND THE MID-ATLANTIC
COAST...

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT FOR
PARTS OF THE CNTRL/SRN PLAINS...

...SYNOPSIS...

AN UPPER-LEVEL LOW ALONG THE MN/ONTARIO BORDER WILL GRADUALLY EVOLVE
INTO AN OPEN WAVE DURING THE D1 PERIOD AS IT PROGRESSES ENEWD INTO
WRN QUEBEC. THIS SYSTEM WILL BE ATTENDED BY A BELT OF 50-60 KT
MIDLEVEL FLOW AND 500-MB HEIGHT FALLS OF 60-120 M/12-HR WHICH WILL
OVERSPREAD THE ST. LAWRENCE VALLEY...LOWER GREAT LAKES...AND NEW
ENGLAND. ELSEWHERE...MIDLEVEL HEIGHTS WILL REBOUND SLIGHTLY ACROSS
THE GREAT PLAINS IN THE WAKE OF THE GREAT LAKES SYSTEM...AND AHEAD
OF AN UPSTREAM UPPER SHORT-WAVE TROUGH TRANSLATING SEWD FROM SRN
BRITISH COLUMBIA THROUGH THE NRN ROCKIES.

AT THE SURFACE...A COLD FRONT INITIALLY FROM LOW PRESSURE OVER WRN
QUEBEC SWWD THROUGH SWRN ONTARIO INTO THE MID-MS VALLEY WILL ADVANCE
EWD INTO NEW ENGLAND AND THE MID-ATLANTIC STATES BY 30/12Z. THE WRN
EXTENSION OF THIS BOUNDARY WILL REMAIN QUASI-STATIONARY...STRETCHING
FROM THE OZARKS WWD TO AN AREA OF LOW PRESSURE OVER WRN OK AT
30/00Z. A DRYLINE IS FORECAST TO EXTEND SWD FROM THE LOW PRESSURE
INTO W-CNTRL TX AND WRN PARTS OF THE EDWARDS PLATEAU REGION AT THIS
TIME. MEANWHILE...TROPICAL DEPRESSION BERYL WILL BEGIN TO
ACCELERATE NEWD FROM S-CNTRL GA THROUGH THE LOWER SAVANNAH RIVER
VALLEY.

...NEW ENGLAND INTO THE LOWER GREAT LAKES AND MID-ATLANTIC
STATES...

AN EXPANSIVE PRE-FRONTAL BAND OF TSTMS IS ONGOING AS OF 12Z FROM
SWRN ONTARIO/LAKE ERIE SWWD INTO NRN KY...LIKELY FORCED BY THE
LEADING EDGE OF STRONGER HEIGHT FALLS ASSOCIATED WITH UPPER SYSTEM
MOVING THROUGH THE GREAT LAKES. BASED ON SATELLITE
IMAGERY...DOWNSTREAM AIR MASS ACROSS NY/PA SHOULD EXPERIENCE STRONG
DAYTIME HEATING. WHEN COUPLED WITH DEWPOINTS IN THE 60S AND
MIDLEVEL LAPSE RATES OF AROUND 7 C/KM...ENVIRONMENT WILL BECOME
MODERATE-STRONGLY UNSTABLE WITH MLCAPE VALUES INCREASING TO
2000-3000 J/KG. THIS DESTABILIZATION ALONG WITH THE EWD PROGRESSION
OF UPPER TROUGH WILL SUPPORT A MARKED INCREASE IN STORM VIGOR AND
COVERAGE BY EARLY AFTERNOON ALONG COLD FRONT AND/OR LEADING EDGE OF
COLD POOL ASSOCIATED WITH THE ONGOING STORMS.

THE STRONGEST MID- AND HIGH-LEVEL WIND FIELD ASSOCIATED WITH THE
TROUGH IS FORECAST TO LAG THE WARM SECTOR TO THE W...LIMITING
DEEP-LAYER SHEAR MAGNITUDES TO GENERALLY 30-40 KT. EXPECT THE
STRONG INSTABILITY TO COMPENSATE WITH ENVIRONMENT BECOMING
SUPPORTIVE OF MULTIPLE ORGANIZED STORM MODES...INCLUDING BOWING LINE
SEGMENTS AND SUPERCELLS WITH THE POTENTIAL FOR CORRIDORS OF WIND
DAMAGE AND SWATHS OF LARGE HAIL. THE GREATEST RISK FOR A TORNADO OR
TWO WILL EXIST ALONG WARM FRONT OVER NEW ENGLAND WHERE LOW-LEVEL
SHEAR WILL BE ENHANCED.

THE SEVERE WEATHER THREAT WILL SPREAD EWD TOWARD THE MID-ATLANTIC
COAST AND WRN NEW ENGLAND BY LATE AFTERNOON INTO THIS EVENING BEFORE
GRADUALLY DIMINISHING LATER TONIGHT WITH THE STABILIZATION OF THE
BOUNDARY LAYER.

...CNTRL/SRN PLAINS...

AS MENTIONED ABOVE...MIDLEVEL HEIGHTS WILL REBOUND SLIGHTLY TODAY
WITH PASSAGE OF SYNOPTIC SYSTEM TO THE NE. AS SUCH...DAYTIME
HEATING AND LOW-LEVEL CONVERGENCE ALONG STATIONARY FRONT AND DRYLINE
WILL BE THE PRIMARY MECHANISMS FORCING TSTM DEVELOPMENT THIS
AFTERNOON. LATEST CONVECTION-ALLOWING AND MESOSCALE MODEL GUIDANCE
INDICATE THAT THE HIGHEST PROBABILITY OF STORM INITIATION WILL BE
ALONG FRONT OVER SRN KS/NRN OK BETWEEN 29/21Z-30/00Z. OTHER
ISOLATED STORMS WILL BE POSSIBLE AT THIS TIME SWWD ALONG THE DRYLINE
INTO W-CNTRL TX.

THE COMBINATION OF STRONG DAYTIME HEATING...BOUNDARY LAYER DEWPOINTS
IN THE 60S...AND STEEP MIDLEVEL LAPSE RATES ARE EXPECTED TO YIELD A
MODERATE-STRONGLY UNSTABLE AIR MASS BY MID-LATE AFTERNOON WITH
MLCAPE VALUES OF 2000-3500 J/KG. WHEN COUPLED WITH A VERTICALLY
VEERING WIND PROFILE AND 40-50 KT OF EFFECTIVE BULK SHEAR...SETUP
WILL BE QUITE FAVORABLE FOR SUPERCELLS CAPABLE OF VERY LARGE HAIL
AND PERHAPS A COUPLE TORNADOES WITHIN THE FIRST FEW HOURS AFTER
STORM INITIATION. WITH TIME...CONVECTION-ALLOWING MODEL GUIDANCE IS
SUGGESTIVE OF UPSCALE GROWTH INTO A SEWD-MOVING BOW ECHO SYSTEM
WHICH WOULD SIGNAL A TRANSITION TO A MORE WIDESPREAD DAMAGING WIND
THREAT ACROSS PORTIONS OF OK...PERHAPS INTO NRN TX TONIGHT.

...FL/ERN GA/SRN SC...

THE COMBINATION OF A MOIST BOUNDARY LAYER AND BREAKS IN CLOUD COVER
WILL YIELD POCKETS OF MODEST DESTABILIZATION TODAY INVOF BERYL.
GIVEN A STILL MODESTLY STRONG WIND FIELD...A LOW PROBABILITY RISK
FOR DAMAGING WINDS AND A TORNADO WILL CONTINUE THROUGH THIS
AFTERNOON.

..MEAD/ROGERS.. 05/29/2012

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