SPC AC 201258
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0658 AM CST WED FEB 20 2008
VALID 201300Z - 211200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A PROGRESSIVE SPLIT FLOW PATTERN WILL PREVAIL OVER THE LWR 48
THROUGH THURSDAY. NRN STREAM SPEED MAX WILL SWEEP RAPIDLY E FROM
THE WRN GRT LKS TO THE NEW ENGLAND CST...WHILE STRONGER SRN BRANCH
SYSTEM NOW OVER CA CONTINUES ESE TO THE AZ/NM BORDER. AT THE
SFC...MAIN PART OF LARGE ARCTIC ANTICYCLONE SHOULD MOVE ESE ACROSS
THE OH VLY TO THE MID ATLANTIC CST...WHILE A SHALLOWER PORTION NOSES
S ACROSS THE SRN HI PLNS. THIS EVOLUTION...COUPLED WITH THE
APPROACH OF AN IMPULSE NOW INVOF BAJA CA IN THE SUBTROPICAL JET...
LIKELY WILL RESULT IN DEVELOPMENT OF AN INVERTED SFC TROUGH OVER
CNTRL/E TX AS A LEE LOW SLOWLY TAKES FORM OVER NE MEXICO.
...SRN/CNTRL PLNS INTO ARKLATEX...
LOW LEVEL MOISTURE IS SPREADING NW ACROSS THE NW GULF AND THE TX
GULF CSTL PLN ATTM. MOISTURE SHOULD CONTINUE TO SPREAD NW ACROSS
THE REMAINDER OF CNTRL/E TX...SRN OK...SW AR AND LA THROUGH EARLY
THURSDAY AS LLJ STRENGTHENS DOWNSTREAM FROM APPROACHING UPR
DISTURBANCES.
ISOLATED TO SCTD TSTMS SHOULD FORM LATE TONIGHT INVOF THE RED RIVER
FROM NW TX/SW OK ESE INTO THE ARKLATEX ON LEADING EDGE OF STRONGEST
ELEVATED MOISTURE FLUX. FORECAST SOUNDINGS OVER THE REGION SHOW
UPWARDS OF 500 J/KG MUCAPE...WITH THE INSTABILITY BASED ABOVE WEAK
EML NEAR 700 MB. COUPLED WITH PRESENCE OF 40-50 KT UNIDIRECTIONAL
WSWLY CLOUD-LAYER SHEAR...SETUP COULD SUPPORT SCTD ELEVATED STORMS
WITH HAIL. EXPECTED DEGREE OF INSTABILITY PRECLUDES ADDITION OF A
SLIGHT RISK AREA ATTM. SHOULD IT BECOME APPARENT...HOWEVER...THAT
MORE ROBUST MOISTURE RETURN WILL BECOME INVOLVED IN THE STORMS THAN
IS NOW EXPECTED...A SLIGHT RISK MAY BE REQUIRED FOR PART OF THE
EXISTING LOW PROBABILISTIC AREA IN LATER OUTLOOKS.
FARTHER N...WIDELY SCTD...MORE STRONGLY-ELEVATED STORMS MAY FORM
LATE IN THE PERIOD ALONG 850 MB THERMAL GRADIENT. THIS ACTIVITY
WOULD EXTEND IN AN ARC FROM WRN/CNTRL KS ESE INTO MO...NE OK...AND
NRN AR. THE STORMS WILL OCCUR ATOP AN ARCTIC AIR MASS AND LIKELY
WILL BE ACCOMPANIED BY FREEZING PRECIPITATION AT THE SFC.
...TX GULF CST INTO CSTL LA...
SCTD SHOWERS ARE EXPECTED TO INCREASE IN COVERAGE FROM THE S TX CSTL
PLN THIS MORNING...NE ACROSS THE MIDDLE AND UPR TX GULF CST BY AFTN
AND EVENING. GRADUAL STRENGTHENING OF WARM LAYER CENTERED NEAR 700
MB /ASSOCIATED WITH ENE ADVECTION OF EML/ SHOULD CAP MUCH OF THE
OVERLAND REGION TO DEEP CONVECTION/TSTMS...ESPECIALLY GIVEN WEAK UVV
AND CLOUD COVER. ISOLATED STORMS MAY...HOWEVER...AFFECT THE CSTL
PLN...AND MORE WIDESPREAD SHOWERS/STORMS MAY DEVELOP OFFSHORE. SOME
OF THE LATTER ACTIVITY COULD AFFECT CSTL LA EARLY THURSDAY...ALONG
LEADING EDGE OF ADVANCING EML.
..CORFIDI.. 02/20/2008
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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