SWODY1
SPC AC 281233
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0733 AM CDT THU MAY 28 2009
VALID 281300Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR
KY/TN SWD ACROSS NW GA AND AL...
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR SW
TX...
...SYNOPSIS...
AMPLIFICATION OF THE LARGE SCALE FLOW REGIME IS UNDERWAY ACROSS THE
CONUS WITH RISING MID LEVEL HEIGHTS OVER THE INTERMOUNTAIN WEST AND
A NRN STREAM TROUGH DIGGING SEWD FROM THE CANADIAN PRAIRIES TO THE
UPPER MS VALLEY. A SEPARATE MID LEVEL TROUGH OVER THE MS
VALLEY...WITH EMBEDDED VORTICITY CENTERS OVER WI AND MO...WILL
PROGRESS EWD TODAY ACROSS THE OH/TN VALLEYS TO THE APPALACHIANS BY
THE END OF THE PERIOD. AN ASSOCIATED WEAK SURFACE CYCLONE IN LOWER
MI WILL DEVELOP NEWD INTO SWRN QUEBEC AS THE NRN STREAM TROUGH AND
MS VALLEY WAVE BEGIN TO PHASE LATE IN THE PERIOD...WHILE A TRAILING
COLD FRONT MOVES EWD INTO OH/KY/TN/AL BY THIS EVENING. THIS FRONT
WILL PROVIDE A PRIMARY FOCUS FOR STRONG/SEVERE THUNDERSTORM
DEVELOPMENT TODAY INTO EARLY TONIGHT...AND OTHER WIDELY SCATTERED
THUNDERSTORMS WILL OCCUR IN THE WARM SECTOR FROM THE CENTRAL
APPALACHIANS SWD TO THE SE ATLANTIC WHERE MOIST AND MODERATELY
UNSTABLE PROFILES WILL PREVAIL.
...TN/OH VALLEY REGION THIS AFTERNOON...
SUBSTANTIAL SURFACE HEATING WILL OCCUR TODAY FROM KY/TN SWD ACROSS
MS/AL IN THE WAKE OF A LEAD SHORTWAVE TROUGH AND CLOUD BAND...AND IN
ADVANCE OF THE SURFACE COLD FRONT. BOUNDARY LAYER DEWPOINTS IN THE
UPPER 60S AND AFTERNOON TEMPERATURES IN THE 80S WILL CONTRIBUTE TO
MLCAPE VALUES NEAR 2000 J/KG. THIS MODERATE INSTABILITY...ALONG
WITH SOME MID LEVEL DRYING AND STEEP LOW-LEVEL LAPSE RATES...WILL
PROMOTE STRONG DOWNDRAFTS AND ISOLATED TO WIDELY-SCATTERED DAMAGING
DOWNBURSTS WITH MULTICELL CLUSTERS IN AN ENVIRONMENT OF MODEST DEEP
LAYER BULK SHEAR. INSTABILITY MAY ALSO BE SUFFICIENT FOR MARGINALLY
SEVERE HAIL WITH THE STRONGEST STORMS.
FARTHER NE ACROSS OH/WRN PA...MORE PERSISTENT/WIDESPREAD CLOUDS WILL
LIMIT INSTABILITY COMPARED TO AREAS FARTHER S...THOUGH
ISOLATED/MARGINALLY SEVERE HAIL AND STRONG WINDS WILL STILL BE
POSSIBLE. FARTHER E ACROSS THE APPALACHIANS AND SE ATLANTIC
COAST...ISOLATED STRONG STORMS WILL BE POSSIBLE...BUT STORMS SHOULD
BE LESS ORGANIZED/PERSISTENT COMPARED TO THE SLIGHT RISK AREA WHERE
VERTICAL SHEAR WILL BE A LITTLE STRONGER.
...RIO GRANDE VALLEY AND SW TX...
A LARGE MCS IS WEAKENING AND MOVING OFF THE LOWER TX COAST THIS
MORNING...IN THE WAKE OF THE PRIOR MCS WHICH IS NOW OVER THE E/SE
GULF OF MEXICO. THE NET EFFECT OF THESE CONVECTIVE SYSTEMS HAS BEEN
TO REDUCE LOW-LEVEL MOISTURE AND MID LEVEL LAPSE RATES OVER S
TX...AND IT APPEARS THE SEVERE THREAT HAS DIMINISHED ACROSS THIS
AREA AS A RESULT. FARTHER NW...LINGERING LOW-LEVEL MOISTURE N OF
THE STALLED FRONT AND ASCENT WITH WEAK SPEED MAXIMA EJECTING NEWD
FROM NRN MEXICO WILL COMBINE WITH DAYTIME HEATING AND SUPPORT
ADDITIONAL THUNDERSTORM DEVELOPMENT TODAY ACROSS W/SW TX. MODEST
DEEP LAYER VERTICAL SHEAR AND MLCAPE VALUES OF 1000-2000 J/KG COULD
AGAIN SUPPORT AT LEAST ISOLATED LARGE HAIL AND STRONG OUTFLOW WINDS
BEFORE CONVECTION WEAKENS BY EARLY TONIGHT.
...FL THIS AFTERNOON...
WLY FLOW REGIME ALOFT AND WEAK SWLY LOW-LEVEL FLOW WILL FAVOR THE E
COAST SEA BREEZE FOR THE STRONGEST AND MOST CONCENTRATED
THUNDERSTORMS THIS AFTERNOON. THERE IS SOME UNCERTAINTY REGARDING
THE INFLUENCE OF THE REMNANT ERN GULF MCS/MCV ON SURFACE HEATING AND
STORM DISTRIBUTION ACROSS FL...BUT WILL MAINTAIN THE 5% WIND/HAIL
PROBABILITIES.
...ORE/NE CA THIS AFTERNOON/EVENING...
DAYTIME HEATING AND LINGERING LOW-MID LEVEL MOISTURE AROUND THE NW
PERIPHERY OF THE GREAT BASIN MID LEVEL RIDGE WILL LIKELY SUPPORT
WIDELY SCATTERED THUNDERSTORM DEVELOPMENT THIS AFTERNOON/EVENING
OVER THE HIGHER TERRAIN OF CENTRAL/S CENTRAL ORE AND NE CA. STEEP
LAPSE RATES IN EXCESS OF 8 C/KM...SEASONALLY COOL MID LEVEL
TEMPERATURES NEAR -12 C AT 500 MB...AND MUCAPE OF 500-1500 J/KG WILL
SUPPORT A FEW SLOW-MOVING STORMS CAPABLE OF PRODUCING ISOLATED LARGE
HAIL AND STRONG DOWNBURST WINDS.
..THOMPSON/SMITH.. 05/28/2009
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