SPC AC 291618
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1118 AM CDT WED APR 29 2009
VALID 291630Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE SRN AND
CENTRAL PLAINS EWD ACROSS AR...
...SYNOPSIS...
BROAD BAND OF LOW AMPLITUDE CYCLONIC FLOW WILL PERSIST ACROSS THE
PLNS...S AND E OF ELONGATING UPR LOW OVER THE PACIFIC NW/NRN RCKYS.
THE LOW SHOULD REDEVELOP E INTO THE NRN PLNS TONIGHT/EARLY THU AS
STRONG SPEED MAX NOW ENTERING THE NRN GRT BASIN CONTINUES ENE INTO
WY AND THE DAKOTAS. FARTHER S...A SPEED MAX IN THE WEAKER SRN
STREAM...NOW OVER NW MEXICO/SRN AZ...SHOULD REACH WRN/CNTRL TX BY
EVE...AND LA/AR EARLY THU.
...SRN PLAINS EWD ACROSS AR...
A RICH GULF AIR MASS IS FEEDING THE LARGE MCS CURRENTLY OVER OK AND
THE HIGH RES MODELS SUGGEST THIS WILL CONTINUE TO BE A THREAT FOR AT
LEAST SEVERE WINDS ON ITS LEADING SQUALL LINE THRU MUCH OF THE DAY.
GIVEN THE AVAILABILITY OF DEWPOINTS WELL INTO THE 60S ACROSS MUCH OF
AR CAPES AOA 1000 J/KG ARE EXPECTED ACROSS AR PRIOR TO THE ARRIVAL
OF THE MCS. ALTHOUGH THE LAPSE RATES WILL BE SOMEWHAT WEAKER THAN
FURTHER W WHERE CURRENT ACTIVITY IS OCCURRING THE WILL DEVELOP COLD
POOL WILL DRIVE THE SQUALL LINE EWD... THEREFORE HAVE EXTENDED THE
SEVERE RISK EWD ACROSS AR TO MS RIVER VALLEY.
IN THE WAKE OF MCS...OUTFLOW BOUNDARY WILL TRAIL WWD ACROSS NRN TX
AND BE FOCUS FOR RENEWED SEVERE THREAT BY MID AFTERNOON. WITH
SUFFICIENT HEATING E OF DRY LINE ACROSS WRN TX THE AIR MASS BECOMES
VERY UNSTABLE WITH MLCAPES TO 3000 J/KG. WHILE LARGE SCALE SUPPORT
IS QUESTIONABLE IN WAKE OF THE MCS...VEERING SHEAR PROFILES COUPLED
WITH THE AMOUNT OF INSTABILITY WILL SUPPORT DEVELOPMENT OF
SUPERCELLS WITH POTENTIAL FOR VERY LARGE HAIL AND AT LEAST ISOLATED
TORNADOES. MORE SCATTERED COVERAGE LIKELY GIVEN LACK OF ANY
PRONOUNCED MID LEVEL IMPULSE...HOWEVER UPPER SPEED MAX DOES PROVIDE
HIGH LEVEL DIVERGENCE. DISCRETE STORMS DO FAVOR POTENTIAL FOR
LONGER LASTING SUPERCELLS THAT WOULD LIKELY INITIATE VICINITY OLD
OUTFLOW BOUNDARIES AS WELL AS ALONG DRY LINE IN FAR W TX AND
CONTINUE LATE INTO THE EVENING.
...CNTRL PLNS...
SFC-BASED INSTABILITY WILL ALSO INCREASE OVER THE CNTRL PLNS TODAY
AS HEATING OCCURS ALONG AXIS OF LOW LVL MOISTURE RETURN WITH LLJ.
THE GREATEST DESTABILIZATION SHOULD OCCUR ALONG WRN EDGE OF THE LLJ
IN WRN KS...WHERE HEATING WILL BE MAXIMIZED BENEATH EML. FARTHER
N...DESTABILIZATION MAY MAXIMIZE ALONG DEVELOPING COLD FRONT/TROUGH
IN WRN/CNTRL NEB AND S CNTRL SD. FORCING FOR ASCENT SHOULD REMAIN
WEAK AS REGION WILL LIE S OF GRT BASIN SPEED MAX AND N OF JET STREAK
AFFECTING THE SRN PLNS. BUT LOW LVL CONVERGENCE ALONG LEE
TROUGH/DRY LINE IN KS...ALONG COLD FRONT IN NEB...AND NEAR TRIPLE
POINT IN SD...SHOULD SUPPORT SCTD AFTN/EVE STORMS. SOME OF THESE
COULD BECOME WEAK SUPERCELLS OR AT LEAST SUFFICIENTLY SUSTAINED TO
YIELD LARGE HAIL/LOCALLY DMGG WIND AND PERHAPS A TORNADO.
..HALES/GRAMS.. 04/29/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z
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