SWODY1
SPC AC 201629
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT TUE SEP 20 2011
VALID 201630Z - 211200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
POTENT UPR LOW NOW OVER ERN ND EXPECTED TO CONTINUE E INTO WRN LK
SUPERIOR BY 12Z WED AS UPSTREAM SPEED MAX NOW OVER SK DROPS S INTO
WRN SD. ELSEWHERE...LINGERING POSITIVE TILT TROUGH/VORT AXIS
EXPECTED TO REMAIN QSTNRY OVER MS/AL AND THE SRN APPALACHIANS.
SFC LOW WITH ND SYSTEM SHOULD BECOME INCREASINGLY OCCLUDED AS COLD
FRONT MOVES E INTO WI LATER TODAY...AND REACHES LK MI EARLY WED.
...UPR GRT LKS/UPR MS VLY TODAY/TNGT...
LOW LVL MOISTURE WILL REMAIN LIMITED IN WARM SECTOR OF UPR MS VLY
SFC LOW...WITH DEWPOINTS IN THE UPR 40S TO LOW 50S F. A PLUME OF
STEEP MID LVL LAPSE RATES...HOWEVER...WILL SWEEP NEWD AHEAD OF FRONT
ACROSS ERN MN AND WI...WHERE MEAGER LOW LVL MOISTURE SHOULD LIMIT
DEVELOPMENT OF BOUNDARY LAYER MIXING-TYPE CLOUDS AND ALLOW SFC TEMPS
TO RISE WELL INTO THE 60S. THUS...DAYTIME HEATING AND FRONTAL
CONVERGENCE MAY SUPPORT DEVELOPMENT OF AN ARC OF WDLY SCTD
LOW-TOPPED SHOWERS AND STORMS IN AN ENVIRONMENT OF 50+ KT DEEP WSWLY
SHEAR.
WITH SHEAR NEARLY PERPENDICULAR TO COLD FRONT...AND SCTD NATURE OF
UPDRAFTS...POTENTIAL WILL EXIST FOR ISOLD SUPERCELLS CAPABLE OF
LOCALLY DMGG WIND FROM NRN AND FAR ERN MN INTO WRN/NRN WI. A
CONDITIONAL THREAT ALSO WILL EXIST FOR A TORNADO OR TWO...ESPECIALLY
IN NW WI AND ADJACENT PARTS OF MN...WHERE OVERLAP OF GREATEST LOW
LVL SRH WITH SBCAPE SHOULD EXIST NEAR SFC LOW AND ASSOCIATED TRIPLE
POINT. HOWEVER...WEAK BUOYANCY /SBCAPE AOB 500 J PER KG/...SHOULD
LIMIT OVERALL STORM COVERAGE/SVR THREAT. IN ADDITION...CONVECTIVE
DEVELOPMENT SWD INTO SRN MN AND IA THROUGH THE DAY MAY BE STYMIED BY
MID LVL SUBSIDENCE/WARMING ON EQUATOR WARD SIDE OF JET STREAK
ROUNDING BASE OF ND UPR LOW. HOWEVER...DEVELOPMENT COULD OCCUR SWD
INTO IA AND IL TNGT AS UPSTREAM IMPULSE BEGINS TO AFFECT REGION.
NEVERTHELESS...GIVEN MARGINAL THERMODYNAMIC ENVIRONMENT...ANY SVR
THREAT SHOULD BECOME INCREASINGLY ISOLD AFTER SUNSET.
...ERN GULF CSTL REGION THIS AFTN/EVE...
INCREASINGLY MOIST LOW LVL ELY FLOW WILL PERSIST OVER THE ERN GULF
CST STATES TODAY...ON SW FRINGE OF WEDGE-TYPE AIR MASS OVER THE
CAROLINAS/N GA. WEAK FORCING FOR ASCENT ASSOCIATED WITH
AFOREMENTIONED UPR IMPULSE AND SFC HEATING MAY SUPPORT AN INCREASE
IN STORMS/SHOWERS FROM CNTRL AL SE INTO SRN GA/N FL.
BUOYANCY AND DEEP SHEAR WILL REMAIN RATHER WEAK. BUT MOISTURE-RICH
LOW LVL ENVIRONMENT WITH ESELY NEAR SFC WINDS MAY ONCE AGAIN SUPPORT
A CONDITIONAL RISK FOR BRIEF TORNADOES/WATERSPOUTS...AND PERHAPS A
STORM OR TWO WITH LOCALLY DMGG WIND...THIS AFTN/EVE.
..CORFIDI/GARNER.. 09/20/2011
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