SWODY1
SPC AC 112000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT SAT JUL 11 2009
VALID 112000Z - 121200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NORTHEAST STATES AND
UPPER OH VALLEY/CENTRAL APPALACHIANS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL HIGH
PLAINS...
...NY/PA TO OH VALLEY/OZARKS...
WELL IN ADVANCE OF SYNOPTIC COLD FRONT...BAND OF STRONG/OCCASIONALLY
SEVERE TSTMS WILL CONTINUE TO PROGRESS EASTWARD ACROSS EASTERN NY
AND PA THROUGH LATE AFTERNOON...WITH DAMAGING WINDS AS THE MAIN
SEVERE THREAT. THIS ACTIVITY MAY CONTINUE TO OUTRUN THE MOST
APPRECIABLE LARGE SCALE FORCING FOR ASCENT/HEIGHT FALLS...WITH CLOUD
COVER/LIMITED HEATING LIKELY TO HINDER VIGOROUS REDEVELOPMENT
FARTHER WEST ALONG THE COLD FRONT...ALTHOUGH AT LEAST ISOLATED
SEVERE TSTMS WILL BE POSSIBLE. OTHER MORE SCATTERED TSTMS AND A
MARGINAL/EPISODIC SEVERE RISK WILL CONTINUE THROUGH AROUND SUNSET
ACROSS THE CENTRAL APPALACHIANS TOWARD THE DELMARVA VICINITY.
FARTHER WEST...OTHER TSTMS MAY DEVELOP/INCREASE THIS AFTERNOON
ACROSS THE MIDDLE MS VALLEY/OZARKS...OR PERHAPS MORE LIKELY LATER
TONIGHT VIA AN INCREASING WSW LOW LEVEL JET. A RATHER MOIST /LOWER
TO MIDDLE 70S F SURFACE DEWPOINTS/ AND UNSTABLE AIRMASS STILL EXISTS
ON THE WESTERN PERIPHERY OF EARLY DAY EXTENSIVE SHOWERS/TSTMS ACROSS
THE LOWER OH VALLEY. DAMAGING WINDS/PERHAPS SOME HAIL WOULD BE THE
PRIMARY SEVERE HAZARDS.
...CENTRAL HIGH PLAINS...
PREVIOUS THINKING REMAINS LARGELY UNCHANGED. STRONG/SEVERE TSTMS ARE
STILL EXPECTED TO DEVELOP LATER THIS AFTERNOON/EARLY EVENING AMIDST
A MOIST UPSLOPE REGIME...MAINLY INITIALLY ALONG THE CO/WY FRONT
RANGE...AND PERHAPS ALONG RESIDUAL WESTWARD-MOVING/STALLING OUTFLOW
VIA EARLY DAY CONVECTION.
..GUYER.. 07/11/2009
.PREV DISCUSSION... /ISSUED 1131 AM CDT SAT JUL 11 2009/
...OH VALLEY INTO PA/NY TODAY...
A BAND OF PRE-FRONTAL THUNDERSTORMS IS MOVING EWD FROM THE LOWER
GREAT LAKES INTO WRN NY/PA/ERN OH...AND OTHER CONVECTION EXTENDS
SWWD TO THE CONFLUENCE OF THE MS/OH RIVERS. BOUNDARY LAYER
DEWPOINTS IN THE MID 60S ACROSS NY AND 68-72 F RANGE FROM OH INTO
KY/WRN TN ARE CONTRIBUTING TO A CORRIDOR OF MODERATE
INSTABILITY...THOUGH ANVIL BLOWOFF FROM THE ONGOING STORMS IS
OVERSPREADING THE WARM SECTOR AND WILL TEND TO SLOW SURFACE HEATING
SOMEWHAT THIS AFTERNOON. IT APPEARS THAT THE CONVECTION WILL
PERSIST THROUGH THE AFTERNOON AND GRADUALLY INTENSIFY AS THE SURFACE
COLD FRONT AND AN ASSOCIATED MID LEVEL TROUGH MOVE EWD FROM THE
GREAT LAKES TOWARD NY/PA...WITH AN ACCOMPANYING THREAT FOR DAMAGING
WINDS AND MARGINALLY SEVERE HAIL.
...CENTRAL HIGH PLAINS THIS AFTERNOON INTO TONIGHT...
ONGOING STORMS ASSOCIATED WITH WAA OVER N CENTRAL NEB ARE EXPECTED
TO WEAKEN BY MIDDAY...BRINGING AN END TO ANY HAIL THREAT IN THE
SHORT TERM. LATER THIS AFTERNOON...SURFACE HEATING IN THE PRESENCE
OF 55-60 F BOUNDARY LAYER DEWPOINTS SHOULD SUPPORT ISOLATED-
SCATTERED THUNDERSTORM DEVELOPMENT FROM THE FRONT RANGE OF CO NWD
INTO E/SE WY. A WEAK MID LEVEL SPEED MAXIMA NOW OVER NRN UT WILL
CREST THE RIDGE AND BEGIN TO IMPACT ERN WY BY LATE EVENING...
POTENTIALLY ENHANCING THUNDERSTORM DEVELOPMENT FROM 00-03Z. GIVEN
AN ENVIRONMENT WITH MLCAPE AOA 2000 J/KG...STEEP MID LEVEL LAPSE
RATES AND EFFECTIVE BULK SHEAR AOA 40 KT...A FEW SUPERCELLS WITH
LARGE HAIL CAN BE EXPECTED. SOME OF THIS CONVECTION MAY PERSIST EWD
OVERNIGHT ACROSS THE PLAINS AS A 20-30 KT LLJ DEVELOPS AND MAINTAINS
LOW-LEVEL WAA AND AN INFLUX OF MOISTURE FROM THE S/SE.
...WRN ND AREA THIS AFTERNOON INTO EARLY TONIGHT...
A MID LEVEL TROUGH OVER SRN AB/SK WILL CONTINUE ESEWD THROUGH
TONIGHT...BRUSHING NRN ND. A WEAK LOW-LEVEL RESPONSE TO THIS WAVE
WILL HELP DRAW RESIDUAL BOUNDARY LAYER DEWPOINTS IN THE LOW-MID 50S
NWWD WHILE SURFACE HEATING SIMULTANEOUSLY CONTRIBUTES TO LOW-LEVEL
DESTABILIZATION. THOUGH INSTABILITY WILL BE LIMITED...FORECAST
HODOGRAPHS ARE FAVORABLE FOR SUPERCELLS...AND THE STRONGEST STORMS
COULD PRODUCE MARGINALLY SEVERE HAIL AND ISOLATED STRONG GUSTS.
...WRN TN/NRN MS AREA THIS AFTERNOON...
A CLUSTER OF STORMS...NOW OVER SRN IL/WRN KY/NW TN...MAY SPREAD SWD
THROUGH THE AFTERNOON ACROSS WRN TN AND NRN MS. A DIFFUSE N-S
BAROCLINIC ZONE...SEPARATING THE SOMEWHAT DRIER/COOLER AIRMASS
ACROSS THE SE STATES FROM THE HOT AIR ACROSS THE SRN PLAINS...AND
WEAK NWLY FLOW ALOFT WILL HELP FOCUS THE CONVECTION ALONG THE
INSTABILITY AXIS...WITH THE POTENTIAL FOR AT LEAST ISOLATED DAMAGING
DOWNBURSTS.
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