SWODY1
SPC AC 040605
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0105 AM CDT TUE MAY 04 2010
VALID 041200Z - 051200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS ERN MN INTO MUCH OF WI
FROM LATE THIS AFTERNOON TO EARLY EVENING...
...SYNOPSIS...
A DEEP-LAYER CYCLONE CENTERED INITIALLY OVER SRN SASKATCHEWAN/ERN MT
WILL PROGRESS ESEWD ALONG THE INTERNATIONAL BORDER TOWARD THE UPPER
MS VALLEY/NWRN ONTARIO THIS FORECAST PERIOD. THIS SYSTEM WILL BE
ACCOMPANIED BY A 90-100 KT MIDLEVEL JET STREAK AND SIGNIFICANT
HEIGHT FALLS THAT WILL OVERSPREAD THE NRN PLAINS AND UPPER MS
VALLEY. A PRECEDING...LOWER-AMPLITUDE SHORTWAVE TROUGH WILL
TRANSLATE EWD FROM THE UPPER OH VALLEY/LOWER GREAT LAKES THROUGH THE
NERN STATES. MEANWHILE...A LOWER LATITUDE TROUGH WILL REMAIN PHASED
WITH THE NERN STATES TROUGH...AND WEAKEN AS IT TRACKS EWD FROM THE
LOWER MS VALLEY THROUGH THE SERN STATES TO OFF THE SERN ATLANTIC
COAST BY 12Z WEDNESDAY.
...UPPER MS VALLEY TO UPPER GREAT LAKES...
A MIDLEVEL IMPULSE/JET STREAK TRACKING EWD WITHIN BASE OF THE NRN
STREAM DEEP-LAYER CYCLONE WILL MOVE QUICKLY EWD FROM THE NRN
ROCKIES...REACHING THE UPPER MS VALLEY LATE THIS AFTERNOON/EARLY
EVENING. A SURFACE LOW EXPECTED TO EVOLVE OVER ERN SD WILL TRACK
INTO ERN MN BY LATE THIS AFTERNOON...AND THEN MOVE NEWD INTO THE
UPPER GREAT LAKES. SEWD EXTENDING WARM FRONT AND TRAILING COLD
FRONT WILL CONCURRENTLY TRANSLATE INTO THE UPPER MS VALLEY BY LATE
AFTERNOON.
MODIFIED CP AIR WITH DEWPOINTS NEAR 50F...POTENTIALLY INTO THE LOWER
50S WITHIN THE WARM SECTOR...WILL ADVECT NNEWD THROUGH THE
UPPER MS VALLEY AND UPPER GREAT LAKES ALONG STRENGTHENING SWLY LLJ
BENEATH PLUME OF 7-7.5 C/KM MIDLEVEL LAPSE RATES. THIS ALONG WITH
DIABATIC HEATING WILL RESULT IN WARM SECTOR MLCAPE 500-1000 J/KG.
UPPER DIVERGENCE WILL INCREASE AS THE IMPULSE/SHORTWAVE TROUGH
APPROACHES THIS REGION. STORMS SHOULD DEVELOP BY LATE AFTERNOON IN
VICINITY OF THE WARM FRONT WHERE ISENTROPIC LIFT WILL BE AUGMENTED
BY THE SWLY LOW LEVEL JET. ADDITIONAL STORMS MAY DEVELOP FARTHER SW
ALONG THE ADVANCING COLD FRONT. STRENGTHENING WIND FIELDS WILL
RESULT IN 40-50 KT DEEP LAYER SHEAR SUFFICIENT FOR UPDRAFT ROTATION.
STEEP LAPSE RATES SUGGEST A THREAT FOR BOTH HAIL AND STRONG/DAMAGING
WIND GUSTS WITH THE STRONGEST ACTIVITY. IN ADDITION...A THREAT FOR
ISOLATED TORNADOES SHOULD EXIST FROM THE SURFACE LOW SEWD ALONG THE
WARM FRONT...WHERE INCREASING LOW LEVEL HODOGRAPH CURVATURE IS
EXPECTED AS THE LLJ STRENGTHENS LATE THIS AFTERNOON/EVENING AND LCLS
SHOULD BE LOWER. A THREAT FOR DAMAGING WINDS MAY CONTINUE INTO THE
EARLY-MID EVENING ACROSS CENTRAL/NRN WI GIVEN FURTHER STRENGTHENING
OF THE WSWLY LLJ /40-45 KT/...WITH THIS THREAT GREATLY DIMINISHING
WITH EWD EXTENT AS DIABATIC COOLING OCCURS.
...PA/NY INTO NEW ENGLAND...
ALTHOUGH A COLD MIDLEVEL TROUGH /-20 TO -24 C AT 500 MB/ WILL MOVE
ACROSS THE NERN STATES TODAY...LIMITED LOW LEVEL MOISTURE WILL
RESULT IN MARGINAL INSTABILITY ACROSS THIS REGION. FORCING FOR
ASCENT SPREADING EWD WITH THE UPPER TROUGH WILL SUPPORT TSTM
DEVELOPMENT FROM LATE MORNING THROUGH THE AFTERNOON/EARLY EVENING.
THE MARGINAL INSTABILITY SHOULD LIMIT THE OVERALL SEVERE WEATHER
THREAT...BUT STEEP LAPSE RATES AND COLD MID LEVEL TEMPERATURES WILL
SUPPORT BOTH ISOLATED HAIL AND STRONG WIND GUSTS WITH THE MORE
ROBUST UPDRAFTS.
...SERN STATES...
AT 12 TODAY...A SURFACE BOUNDARY IS EXPECTED TO EXTEND FROM THE
CAROLINA COASTS TO THE CENTRAL GULF COAST. THIS BOUNDARY WILL MOVE
S/SEWD TODAY. AN EXTENSIVE AREA OF CLOUDS WITH SHOWERS AND A FEW
EMBEDDED TSTMS WILL LIKELY BE ONGOING FROM THE FL PANHANDLE NEWD
INTO THE ERN CAROLINAS IN VICINITY OF THE BAROCLINIC ZONE. DESPITE
THE PRESENCE OF RICH LOW LEVEL MOISTURE...WEAK MIDLEVEL LAPSE RATES
AND LIMITED SURFACE HEATING WILL RESULT IN A MARGINAL THERMODYNAMIC
ENVIRONMENT. MODELS CONTINUE TO SUGGEST THE SRN STREAM SHORTWAVE
TROUGH AND ITS ATTENDANT MID-UPPER JET FORECAST TO REMAIN IN POST
FRONTAL ZONE AS IT ADVANCES EWD. THUS...DEEP LAYER FLOW AND
VERTICAL SHEAR WILL NOT BE PARTICULARLY STRONG IN THE WARM SECTOR.
HOWEVER...AN ISOLATED STRONG WIND GUST OR TWO CANNOT BE RULED OUT
WHERE SUFFICIENT BOUNDARY LAYER DESTABILIZATION OCCURS.
..PETERS/JIRAK.. 05/04/2010
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