DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 271253
SWODY1
SPC AC 271251

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0751 AM CDT SUN MAY 27 2012

VALID 271300Z - 281200Z

...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT
ACROSS PARTS OF KS AND NEB...

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT FROM
THE UPPER MS VALLEY AND UPPER GREAT LAKES INTO PARTS OF THE
CNTRL/SRN PLAINS...

...SYNOPSIS...

MID/UPPER-LEVEL LOW OVER ERN ID/SWRN MT WILL PROGRESS NEWD INTO THE
NRN PLAINS THIS PERIOD...SUPPRESSING RIDGE AXIS CURRENTLY PRESENT
ACROSS THE UPPER GREAT LAKES. WITHIN THIS BROAD-SCALE
PATTERN...LEAD VORTICITY MAXIMUM OVER THE NRN HIGH PLAINS WILL PIVOT
NWD INTO SRN SASKATCHEWAN/MANITOBA IN ADVANCE OF THE NEXT UPSTREAM
PERTURBATION WHICH WILL TRACK FROM THE LOWER CO VALLEY INTO CNTRL
HIGH PLAINS BY THIS EVENING. THESE IMPULSES ARE SITUATED ALONG THE
CYCLONIC SIDE OF A 70-80 KT MIDLEVEL JET STREAK WHICH WILL EXTEND
FROM THE ERN DAKOTAS SWWD INTO THE SRN ROCKIES BY 28/00Z.
ELSEWHERE...LATEST NHC GUIDANCE INDICATES THAT SUBTROPICAL STORM
BERYL WILL MAKE LANDFALL LATER TODAY OR TONIGHT BEFORE DECELERATING
OVER NERN FL/SERN GA BY 28/12Z.

AT THE SURFACE...LOW PRESSURE OVER N-CNTRL SD WILL DEVELOP NNEWD
THROUGH THE RED RIVER VALLEY IN TANDEM WITH OUTFLOW-REINFORCED WARM
FRONT WHICH WILL REACH THE UPPER GREAT LAKES TONIGHT. TRAILING
PACIFIC FRONT/DRYLINE WILL ADVANCE EWD...LIKELY EXTENDING FROM THE
ERN DAKOTAS SSWWD THROUGH CNTRL NEB...WRN/CNTRL KS INTO THE ERN TX
PNHDL AND W-CNTRL TX BY 28/00Z. THIS BOUNDARY WILL BE THE PRIMARY
FOCUS FOR SEVERE TSTM DEVELOPMENT THIS AFTERNOON INTO TONIGHT.

...UPPER MS VALLEY/UPPER GREAT LAKES INTO CNTRL/SRN PLAINS...

A BROAD ZONE OF WAA/ISENTROPIC ASCENT AT THE TERMINUS OF A 50+ KT
LLJ IS SUSTAINING A CORRIDOR OF ELEVATED SHOWERS AND TSTMS N OF
SYNOPTIC WARM FRONT FROM ERN ND TO LOWER MI. THIS ACTIVITY SHOULD
GRADUALLY DECREASE IN AREAL COVERAGE AND/OR MOVE N OF THE
INTERNATIONAL BORDER THIS MORNING AS THE LLJ MIGRATES NWD THROUGH
THE UPPER MS VALLEY/UPPER GREAT LAKES. ISOLATED OCCURRENCES OF HAIL
WILL BE POSSIBLE WITH THESE STORMS...AS WILL LOCALLY STRONG WIND
GUSTS. THIS IS ESPECIALLY THE CASE ACROSS PORTIONS OF LOWER MI IN
ASSOCIATION WITH A FORWARD-PROPAGATING MCS MOVING ESEWD ACROSS THE
AREA.

IN THE WAKE OF THE ELEVATED STORMS...DAYTIME HEATING...COUPLED WITH
BOUNDARY LAYER DEWPOINTS IN THE 60S AND STEEP LAPSE RATES WILL YIELD
A MODERATE TO STRONGLY UNSTABLE WARM SECTOR BY LATE AFTERNOON WITH
MLCAPE VALUES APPROACHING 1500-3000 J/KG. LATEST
CONVECTION-ALLOWING AND MESOSCALE MODEL GUIDANCE IS IN RATHER GOOD
AGREEMENT IN SUGGESTING THAT SURFACE-BASED TSTM DEVELOPMENT WILL
BECOME INCREASINGLY LIKELY BY 27/21Z ALONG THE PACIFIC FRONT/DRYLINE
FROM CNTRL MN SWWD THROUGH CNTRL NEB INTO N-CNTRL KS. THE PRESENCE
OF 35-45 KT OF DEEP-LAYER SHEAR WILL BE SUPPORTIVE OF SUPERCELLS AS
THE INITIAL STORM MODE. THE MAJORITY OF CONVECTION-PERMITTING DATA
SETS INDICATE THE POTENTIAL FOR A RAPID COALESCENCE OF STORMS INTO
AN MCS ACROSS THE MID-MO VALLEY WHERE THE DEEP-LAYER SHEAR VECTORS
WILL BE ORIENTED NEARLY PARALLEL TO THE INITIATING BOUNDARY. LARGE
HAIL AND DAMAGING WINDS WILL BE THE PRIMARY HAZARDS WITH THESE
STORMS.

A COUPLE OF AREAS OF RELATIVELY GREATER TORNADO POTENTIAL MAY
DEVELOP LATE THIS AFTERNOON INTO EVENING...ONE ALONG THE WARM FRONT
ACROSS MN/NWRN WI...AND THE OTHER INVOF OF A SECONDARY SURFACE LOW
OVER S-CNTRL NEB/N-CNTRL KS. IN THE FORMER...A MORE MOIST/LOW-LCL
BOUNDARY LAYER WILL COINCIDE WITH LOCAL MAXIMUM IN STREAMWISE
VORTICITY...SUGGESTING AN INCREASED RISK FOR TORNADOES AS STORMS
CROSS THE BOUNDARY. FOR THE LATTER...MODEL GUIDANCE INDICATES THAT
POTENTIALLY SIZABLE T-TD SPREADS AND MODEST LOW-LEVEL SHEAR WILL
LIMIT TORNADO POTENTIAL INTO EARLY EVENING. HOWEVER...IN THE
28/00-03Z TIME FRAME...A GRADUALLY COOLING BOUNDARY LAYER /I.E.
LOWERING LCL HEIGHTS/ AND NOCTURNAL INCREASE IN THE LLJ MAY ENHANCE
TORNADO POTENTIAL WITH ANY ONGOING SUPERCELLS.

...GA/FL...

OUTER ENVELOPE OF STRONGER WIND FIELD ASSOCIATED WITH BERYL HAS
ALREADY OVERSPREAD THE SERN ATLANTIC COAST WITH THE 12Z CHS SOUNDING
SHOWING LOW-LEVEL ELY FLOW OF AROUND 30 KT JUST ABOVE GROUND.
EXPECT LOW-LEVEL WIND FIELD /AND RESULTING SHEAR/ TO FURTHER
INCREASE TODAY WITH THE POTENTIAL FOR ROTATING STORMS EMBEDDED
WITHIN SYSTEM RAINBAND/S/ TO APPROACH THE COAST. TEMPERATURE
INVERSION NOTED JUST BELOW 700 MB ON THE 12Z CHS IS OBSERVED TO
PERSIST THROUGH THE DAY IN SOME OF THE MODEL-DERIVED FORECAST
SOUNDINGS WHICH TEMPERS THE DEGREE OF AIR MASS DESTABILIZATION. AS
SUCH...LOW /2 PERCENT/ TORNADO PROBABILITIES WILL BE MAINTAINED IN
THIS FORECAST.

...LOWER GREAT LAKES/NRN MID-ATLANTIC STATES...

MORNING SURFACE ANALYSIS SHOWS A STALLED FRONT FROM NRN/CNTRL NJ WWD
ACROSS SRN PA INTO CNTRL OH. THIS BOUNDARY WILL BE THE FOCUS FOR
TSTMS TODAY INTO THIS EVENING AS REGION IS GLANCED BY A SERIES OF
WEAK IMPULSES APPROACHING FROM THE NW. VERTICAL SHEAR WILL REMAIN
WEAK...BUT THE PRESENCE OF A MOIST AND MODERATELY UNSTABLE
ENVIRONMENT /MLCAPE OF 1000-1500 J PER KG/ MAY SUPPORT A FEW SEVERE
STORMS CAPABLE OF SOME HAIL AND LOCALLY DAMAGING WIND GUSTS.

IT IS ALSO POSSIBLE THAT SOME REMNANT OF MCSS ONGOING ACROSS LOWER
MI COULD PERSIST AND EVENTUALLY MOVE ACROSS LAKE ERIE BY MID
AFTERNOON. SHOULD THIS SCENARIO UNFOLD...A RISK FOR DAMAGING WINDS
AND SOME HAIL WILL EXIST WITH THIS ACTIVITY INTO MID/LATE EVENING.

..MEAD/ROGERS.. 05/27/2012

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