SWODY2
SPC AC 271729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT FRI MAY 27 2011
VALID 281200Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CENTRAL HIGH PLAINS
THROUGH THE LOWER MO VALLEY TO MIDWEST...
...SYNOPSIS...
THE UPPER FLOW PATTERN IS EXPECTED TO AMPLIFY ON SATURDAY AS A BROAD
TROUGH...NOW LOCATED OFF THE PACIFIC NW COAST...DIGS SEWD EVOLVING
INTO A CLOSED LOW CENTERED OVER CENTRAL CA/NV BY 12Z SUNDAY. THIS
WILL RESULT IN DOWNSTREAM HEIGHT RISES FROM THE LOWER-MID MS VALLEY
TO MUCH OF THE ATLANTIC SEABOARD...WITH ZONAL FLOW ALOFT
TRANSITIONING TO DEEP SWLY AND EXTENDING FROM THE GREAT BASIN/FOUR
CORNERS TO THE GREAT LAKES. MEANWHILE...OVER THE NRN STATES...A
SHORTWAVE TROUGH WILL TRACK FROM WI TO NRN QUEBEC...WITH A SECOND
SHORTWAVE TROUGH SHIFTING ENEWD FROM NRN ND INTO ONTARIO.
...CENTRAL PLAINS THROUGH MID MS VALLEY/MIDWEST...
ALTHOUGH HEIGHTS WILL BE GRADUALLY RISING...MODELS SUGGEST A COUPLE
OF WEAK IMPULSES EMBEDDED ALONG SRN EXTENT OF STRONGER FLOW ALOFT
SHOULD TRANSLATE ENEWD THROUGH THE LOWER MO VALLEY TO MIDWEST
SATURDAY AFTERNOON. A SURFACE FRONT ATTENDANT TO THE WI SHORTWAVE
THROUGH WILL ADVANCE EWD ACROSS THE GREAT LAKES...WHILE THE SRN
EXTENT BECOME QUASI-STATIONARY FROM NRN IND/CENTRAL IL THROUGH
CENTRAL MO TO ALONG THE OK/KS BORDER. THE OK/KS AND MO PORTION OF
THIS BOUNDARY SHOULD RETREAT NWD AS A WARM FRONT SATURDAY NIGHT AS
SLY LLJ STRENGTHENS INTO KS/MO.
ALTHOUGH MODELS SHOW GRADUAL HEIGHT RISES AND WEAK UPPER
FORCING...DESTABILIZATION/MODERATE INSTABILITY ALONG THE
QUASI-STATIONARY BOUNDARY AND STRONG EFFECTIVE BULK SHEAR /40-50 KT/
SUGGEST ORGANIZED STORMS WILL BE POSSIBLE SATURDAY AFTERNOON AND
EVENING. GENERAL MODEL AGREEMENT DOES SUGGEST THE GREATEST
POTENTIAL FOR ORGANIZED TSTMS AND ATTENDANT SEVERE WEATHER THREAT
WILL EXIST FROM ERN KS THROUGH CENTRAL/NRN MO INTO IL.
...CENTRAL HIGH PLAINS TO NRN KS/SRN NEB...
POTENTIAL EXISTS FOR THE ATMOSPHERE TO DESTABILIZE WITHIN UPSLOPE
REGIME OVER ERN CO AS UPPER 40S TO NEAR 50 F DEWPOINTS ADVECT WWD
BENEATH STEEP LAPSE RATES NORTH OF SURFACE LOW OVER THE SRN HIGH
PLAINS. MODELS SUGGEST MUCAPE TO AROUND 1000 J/KG WILL BE POSSIBLE
OVER ERN CO DURING PEAK HEATING. STRONG /60+ KT/ EFFECTIVE SHEAR
WILL SUPPORT SUPERCELLS. THIS AREA HAS BEEN INCLUDED IN THE SLIGHT
RISK. THIS ACTIVITY SHOULD PROPAGATE EWD INTO NWRN KS SATURDAY
EVENING...WITH ADDITIONAL STORMS DEVELOPING EWD ACROSS NRN KS/SRN
NEB AS LOW LEVEL WAA INCREASES ALONG NOSE OF A 50 KT SSWLY LLJ.
AFTER DARK...STRONG EFFECTIVE BULK SHEAR AND MODERATE ELEVATED
INSTABILITY ARE EXPECTED TO SUPPORT ELEVATED STORMS PRODUCING A
THREAT FOR HAIL.
...MN...
COLD AIR ALOFT WITH -20 TO -22 C AT 500 MB AND DIABATIC WARMING WILL
RESULT IN DESTABILIZATION DURING THE DAY...BUT MEAGER LOW LEVEL
MOISTURE WILL LIKELY LIMIT MLCAPE TO AOB 500 J/KG. A FEW STORMS
WILL LIKELY DEVELOP WITHIN ZONE OF FORCING ALONG AND AHEAD OF FRONT
AS THE ND SHORTWAVE TROUGH AND A PACIFIC IMPULSE SPREAD ACROSS MN
SATURDAY AFTERNOON. ISOLATED LARGE HAIL AND STRONG TO DAMAGING WIND
GUSTS WILL BE POSSIBLE...BUT THE EXPECTED MARGINAL THERMODYNAMIC
ENVIRONMENT PRECLUDES MORE THAN 5% SEVERE PROBABILITIES AT THIS
TIME.
...CENTRAL/ERN PA...NY AND VT...
A MIDLEVEL TROUGH...CURRENTLY MOVING THROUGH THE UPPER OH VALLEY/
CENTRAL APPALACHIANS...WILL WEAKEN SUBSTANTIALLY AS IT TRACKS FROM
PA THROUGH NRN NEW ENGLAND AND THE SAINT LAWRENCE RIVER VALLEY. AT
12Z SATURDAY...SHOWERS AND A FEW TSTMS SHOULD BE ONGOING FROM NY SWD
TO THE ERN CAROLINAS WITHIN DIFFLUENT UPPER LEVEL FLOW REGIME ACROSS
THIS AREA. THE WEAK WAVE TRACKING NEWD IS EXPECTED TO SUPPORT
ADDITIONAL TSTM DEVELOPMENT PRIMARILY FROM THE MID ATLANTIC COAST TO
CENTRAL/ERN NY AND VT AS THE STRONG PACIFIC JET NOSES INTO THE GREAT
LAKES TO SRN ONTARIO/QUEBEC MAINTAINING DIFFLUENT FLOW. ALTHOUGH
WIND FIELDS WILL BE WEAKENING THIS FORECAST PERIOD... VERTICALLY
VEERING PROFILES AND EFFECTIVE BULK SHEAR /25-35 KT/ SUGGESTS
MULTICELLS AND A SUPERCELL OR TWO WILL BE POSSIBLE. ACTIVITY SHOULD
DEVELOP EARLY IN THE FORECAST PERIOD GIVEN A WEAKLY CAPPED MOIST
ENVIRONMENT. HOWEVER...WEAK INSTABILITY SHOULD LIMIT THE COVERAGE
OF STRONGER/SEVERE STORMS...AND THUS MAINTAIN LOW SEVERE
PROBABILITIES.
..PETERS.. 05/27/2011
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