DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 281252
SWODY1
SPC AC 281250

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0750 AM CDT MON MAY 28 2012

VALID 281300Z - 291200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
ACROSS PORTIONS OF THE UPPER MS VALLEY...UPPER GREAT LAKES...AND
MIDWEST...

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
ACROSS PARTS OF THE SRN PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING FOR
A PORTION OF THE NERN U.S...

...SYNOPSIS...

A PROGRESSIVE LARGE-SCALE PATTERN WILL BE MAINTAINED THROUGH THE D1
PERIOD WITH THE PRIMARY FEATURE OF INTEREST BEING AN UPPER LOW WHICH
WILL TRANSLATE EWD ACROSS THE N-CNTRL CONUS. A LEAD VORTICITY
MAXIMUM AND ATTENDING BELT OF 50-60 KT MIDLEVEL FLOW FROM THE UPPER
MS VALLEY INTO MID MO VALLEY WILL ADVANCE NEWD THROUGH THE UPPER
GREAT LAKES TODAY...CONTRIBUTING TO 500-MB HEIGHT FALLS APPROACHING
50-100 M. ELSEWHERE...TROPICAL STORM BERYL IS EXPECTED TO STALL
OVER S-CNTRL GA/N-CNTRL FL BEFORE BEGINNING TO ACCELERATE NEWD
LATE.

AT THE SURFACE...LOW PRESSURE OVER CNTRL MN WILL DEVELOP NEWD
THROUGH LAKE SUPERIOR INTO SWRN ONTARIO IN CONJUNCTION WITH THE LEAD
IMPULSE MENTIONED ABOVE. A TRAILING COLD FRONT WILL ADVANCE EWD
THROUGH THE UPPER GREAT LAKES WITH THE SWRN EXTENSION OF BOUNDARY
STALLING ACROSS THE SRN PLAINS. MEANWHILE...STRENGTHENING LOW-LEVEL
WAA WILL RESULT IN THE NWD/NEWD ADVANCEMENT OF A WARM FRONT ACROSS
THE NERN STATES.

...UPPER GREAT LAKES AND MID MS VALLEY...

A PRE-FRONTAL BAND OF TSTMS IS ONGOING AS OF 12Z FROM SWRN WI TO
N-CNTRL MO...LIKELY BEING FORCED BY DCVA ATTENDANT TO LEAD VORTICITY
MAXIMUM MENTIONED ABOVE. LATEST CONVECTION-ALLOWING MODEL GUIDANCE
SUGGESTS THAT THIS ACTIVITY SHOULD DIMINISH THIS MORNING WITH
RENEWED STORM DEVELOPMENT ANTICIPATED ALONG COLD FRONT IN THE 18-21Z
TIME FRAME FROM CNTRL/ERN WI INTO ERN IA. BY THIS TIME...THE
COMBINATION OF SLIGHT BOUNDARY LAYER MOISTENING...DAYTIME
HEATING...AND MIDLEVEL COOLING WILL YIELD A MODERATELY UNSTABLE AIR
MASS WITH MLCAPE VALUES APPROACHING 1000-2000 J/KG.

MODEL-DERIVED HODOGRAPHS DEPICT LARGELY UNIDIRECTIONAL...SWLY WINDS
WITH 35-50 KT OF DEEP-LAYER SHEAR WHICH WILL SUPPORT ORGANIZED STORM
MODES...INCLUDING SUPERCELLS AND BOWING STRUCTURES CAPABLE OF MAINLY
DAMAGING WINDS AND LARGE HAIL. EXPECT STORMS TO COALESCE INTO
MULTIPLE CLUSTERS OR A BROKEN LINE WITH THE SEVERE WEATHER THREAT
SPREADING ACROSS LOWER MI...NRN/CNTRL IL...AND NRN IND LATE THIS
AFTERNOON AND EVENING.

...UPPER MS VALLEY...

ONGOING CLUSTER OF TSTMS OVER SERN ND/NERN SD APPEARS TO BE
ASSOCIATED WITH A MORE COMPACT VORTICITY MAXIMUM ROTATING THROUGH
SERN QUADRANT OF UPPER LOW. IN FACT...THIS FEATURE APPEARS TO BE
REFLECTED AT THE SURFACE BY A WEAK LOW AND SECONDARY COLD FRONT OVER
THE DAKOTAS. LATEST MODEL GUIDANCE SUGGESTS THAT THIS CORRIDOR OF
ENHANCED FORCING WILL SHIFT EWD INTO MN BY AFTERNOON WITH ASSOCIATED
SECONDARY COLD FRONT FOCUSING TSTM DEVELOPMENT. COLD TEMPERATURES
ALOFT...DAYTIME HEATING AND RESIDUAL DEWPOINTS IN THE 50S WILL
SUPPORT MODEST DESTABILIZATION AND A FEW SEVERE STORMS WILL BE
POSSIBLE WITH A RISK FOR HAIL AND DAMAGING WINDS.

...SRN PLAINS...

COLD FRONT CURRENTLY FROM WRN OK INTO TX SOUTH PLAINS AND SERN NM
WILL CONTINUE TO SETTLE SWD THIS MORNING BEFORE STALLING IN RESPONSE
TO THE DEVELOPMENT OF A THERMAL LOW OVER THE LOW ROLLING PLAINS OF
TX THIS AFTERNOON. AIR MASS TO THE S OF THE FRONT IS EXPECTED TO
BECOME QUITE HOT. WHEN COMBINED WITH STEEP MIDLEVEL LAPSE RATES AND
BOUNDARY LAYER DEWPOINTS IN THE 60S...EXPECT MLCAPE VALUES TO
INCREASE TO 2000-3000 J/KG.

LARGE-SCALE FORCING FOR ASCENT WILL REMAIN NEGLIGIBLE THROUGH THE
PEAK OF THE DIURNAL HEATING CYCLE. HOWEVER...THE STRONG HEATING AND
CONVERGENCE ALONG FRONT --AND ESPECIALLY E/NE OF SURFACE LOW-- WILL
GIVE RISE TO WIDELY SCATTERED TSTM DEVELOPMENT. GIVEN A KINEMATIC
ENVIRONMENT FEATURING VERTICALLY VEERING WINDS WITH HEIGHT AND 35-45
KT OF DEEP WNWLY SHEAR...SETUP WILL FAVOR THE DEVELOPMENT OF
SUPERCELLS CAPABLE OF VERY LARGE HAIL AND DAMAGING WINDS. STORMS
MAY MERGE INTO A SEWD-MOVING MCS THIS EVENING WITH A CONTINUED RISK
FOR ISOLATED DAMAGING WINDS AND HAIL PERSISTING INTO TONIGHT.

...NORTHEASTERN STATES...

LOWER TO MID-TROPOSPHERIC WAA WILL PERSIST TODAY IN CONJUNCTION WITH
BUILDING MIDLEVEL RIDGE AXIS DOWNSTREAM FROM N-CNTRL CONUS TROUGH.
THIS WILL RESULT IN THE GRADUAL NWD/NEWD ADVANCEMENT OF SURFACE WARM
FRONT ACROSS THE LOWER GREAT LAKES REGION AND WRN/CNTRL NEW ENGLAND.
VISIBLE SATELLITE IMAGERY SHOWS THAT STRONG DIABATIC WARMING SHOULD
OCCUR WITHIN WARM SECTOR...WHICH WHEN COMBINED WITH DEWPOINTS IN THE
60S AND AN EWD-ADVECTING EML/STEEP LAPSE RATE PLUME...WILL RESULT IN
MODERATE AFTERNOON INSTABILITY WITH MLCAPE OF 1500-2500 J/KG.

WHILE SPECIFIC DETAILS OF STORM EVOLUTION REMAIN UNCLEAR...IT IS
LIKELY THAT THE WARM FRONT WILL BE A FOCUS FOR DEVELOPMENT THIS
AFTERNOON. ALSO RESIDUAL COLD POOL ASSOCIATED WITH ELEVATED TSTM
CLUSTER OVER LAKE ONTARIO MAY PROMOTE RENEWED STORM DEVELOPMENT BY
LATE MORNING/EARLY AFTERNOON ACROSS PORTIONS OF UPSTATE NY /REF. MCD
935/.

REGION WILL REMAIN ON SRN PERIPHERY OF HIGHER MOMENTUM MIDLEVEL FLOW
CRESTING BUILDING RIDGE AXIS WITH GENERALLY 30-35 KT OR LESS OF
DEEP-LAYER SHEAR. NEVERTHELESS...THE DEGREE OF INSTABILITY SHOULD
COMPENSATE WITH THE POTENTIAL FOR ORGANIZED MULTICELL CLUSTERS AND
MARGINAL SUPERCELL STORM MODES. LARGE HAIL AND DAMAGING WINDS WILL
BE THE PRIMARY HAZARDS WITH THE MOST INTENSE STORMS THROUGH MID-LATE
EVENING BEFORE THE AIR MASS BEGINS TO STABILIZE WITH THE COOLING OF
THE BOUNDARY LAYER.

..MEAD/ROGERS.. 05/28/2012

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