SWODY1
SPC AC 111639
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1139 AM CDT THU JUN 11 2009
VALID 111630Z - 121200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO EARLY
TONIGHT FROM N TX ENEWD TO VA...
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR THE
HIGH PLAINS OF ERN CO/WRN KS...
...MIDDLE TN EWD TO THE SRN APPALACHIANS THIS AFTERNOON...
A WELL-DEFINED MCV IS MOVING EWD OVER MIDDLE TN AS OF LATE MORNING.
THIS SYSTEM IS ACCOMPANIED BY A NARROW BELT OF 40-50 KT MID LEVEL
FLOW...AND IS PRECEDED BY A MOIST AND MODERATELY UNSTABLE AIR MASS.
EXPECT THE CONVECTION WITH THE MCV TO PERSIST INTO THE AFTERNOON
WHILE SPREADING EWD OVER ERN TN AND ADJACENT AREAS...WITH A
CONTINUED THREAT FOR DAMAGING WINDS AND ISOLATED LARGE HAIL.
ADDITIONALLY...THERE WILL BE THE POSSIBILITY OF ISOLATED/BRIEF
TORNADOES WHERE THE CONVECTIVE CLUSTER INTERSECTS AND MOVES EWD
ALONG A RESIDUAL E-W OUTFLOW BOUNDARY ACROSS ERN TN...IN THE WAKE OF
THE WEAKENING CLUSTER NOW APPROACHING THE BLUE RIDGE.
...S CENTRAL PA SWD INTO CENTRAL VA/NRN NC THIS AFTERNOON...
THE REMNANTS OF A WEAKENING OVERNIGHT MCS ARE CROSSING THE BLUE
RIDGE AS OF 16Z...AND THIS SYSTEM WILL CONTINUE EWD ACROSS SRN
PA/MD/CENTRAL VA/NRN NC THROUGH THIS AFTERNOON. MID LEVEL LAPSE
RATES ARE RATHER POOR OVER THE REGION /AOB 6 C/KM BASED ON 12Z
SOUNDINGS/...BUT SOME SURFACE HEATING AND A MOIST BOUNDARY LAYER
WITH DEW POINTS IN THE MID-UPPER 60S WILL RESULT IN SUFFICIENT
DESTABILIZATION /MLCAPE OF 1000-1500 J/KG FOR SEVERE
STORMS...ESPECIALLY ACROSS VA AND NC. THE NWD EXTENT OF THE
STRONGER DESTABILIZATION COULD BE LIMITED BY PERSISTENT CLOUDS FROM
NRN VA INTO SRN PA. MEANWHILE...STRENGTHENING MID LEVEL FLOW
ACCOMPANIES THE REMNANT CONVECTIVE SYSTEM MOVING OVER VA FROM THE
W...AND IT APPEARS PROBABLE THAT NEW STORMS WILL FORM THIS AFTERNOON
IN A N-S BAND ALONG THE REMNANT OUTFLOW BOUNDARY AS IT PROGRESSES
EWD ACROSS THE PIEDMONT. DAMAGING WINDS WILL BE THE PRIMARY SEVERE
THREAT WITH BOWING SEGMENTS...THOUGH ISOLATED LARGE HAIL WILL ALSO
BE POSSIBLE.
...NW/N CENTRAL INTO E TX THROUGH EARLY TONIGHT...
ONGOING CONVECTION IN N/NE TX IS BEING MAINTAINED BY WAA ABOVE THE
SHALLOW COLD POOL GENERATED BY OVERNIGHT AND EARLY MORNING STORMS.
THE 12Z FWD SOUNDING SHOWED STRONG ELEVATED INSTABILITY /MUCAPE IN
EXCESS OF 3000 J/KG/...WHILE OTHER SOUNDINGS TO THE S REVEALED A
LITTLE STRONGER CAP. THERE IS SOME UNCERTAINTY REGARDING THE
SHORT-TERM EVOLUTION OF THE STORMS GIVEN AN EXPECTED WEAKENING OF
THE SWLY LLJ THAT HAS BEEN FEEDING THIS CONVECTION.
HOWEVER...DIURNAL WEAKENING OF THE CAP THROUGH DAYTIME HEATING AND
NEW COLD POOL GENERATION COULD ALSO ALLOW STORMS TO ROOT CLOSER TO
THE SURFACE AND BEGIN TO PROPAGATE SEWD AS AN MCS WITH DAMAGING
WINDS AND LARGE HAIL.
FARTHER W/NW...A SURFACE COLD FRONT IS SAGGING SWD ACROSS THE TX
PANHANDLE INTO NW TX...WHERE THE BOUNDARY INTERSECTS THE WWD
EXTENSION OF THE OUTFLOW FROM THE N TX STORMS. STRONG SURFACE
HEATING AND A NARROW CORRIDOR OF UPPER 50S TO MID 60S BOUNDARY LAYER
DEW POINTS COULD SUPPORT ISOLATED THUNDERSTORM DEVELOPMENT LATE THIS
AFTERNOON ALONG THE FRONT FROM THE SE TX PANHANDLE ESEWD INTO NW TX.
DEEP LAYER VERTICAL SHEAR AND INSTABILITY WILL BE SUFFICIENT FOR
SUPERCELLS...AND A TORNADO OR TWO COULD OCCUR WITH STORMS RIDING
ESEWD ALONG THE IMMEDIATE COOL SIDE OF THE FRONT WHERE SOMEWHAT
RICHER LOW-LEVEL MOISTURE AND STRONGER LOW-LEVEL SHEAR WILL COINCIDE
THIS EVENING.
...ERN CO/WRN KS THROUGH TONIGHT...
MOIST POST-FRONTAL UPSLOPE WILL CONTINUE ACROSS CO TODAY AS
LOW-LEVEL FLOW VEERS TO MORE ELY/SELY IN RESPONSE TO THE APPROACH OF
A MID LEVEL TROUGH MOVING ENEWD FROM UT/AZ. LAPSE RATES ARE
RELATIVELY POOR OVER THE HIGH PLAINS IN THE MOIST ENVIRONMENT...BUT
DAYTIME HEATING IN CLOUD BREAKS AND BOUNDARY LAYER DEW POINTS IN THE
LOW-MID 50S WILL SUPPORT AFTERNOON MLCAPE VALUES OF 500-1000 J/KG.
THIS MODEST INSTABILITY...IN COMBINATION WITH EFFECTIVE BULK SHEAR
AOA 50 KT AND INCREASING LOW-LEVEL SHEAR LATER THIS
AFTERNOON/EVENING...WILL BE SUPPORTIVE OF A FEW SUPERCELLS FORMING
JUST E OF THE MOUNTAINS AND MOVING EWD ONTO THE PLAINS OF ERN CO.
ISOLATED LARGE HAIL AND DAMAGING WINDS WILL BE THE MOST COMMON
THREAT...THOUGH A COUPLE OF TORNADOES CAN ALSO BE EXPECTED THIS
AFTERNOON/EVENING BEFORE CONVECTION BECOMES SLIGHTLY ELEVATED
FARTHER E INTO WRN KS.
..THOMPSON/SMITH.. 06/11/2009
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