SPC AC 292002
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0302 PM CDT WED APR 29 2009
VALID 292000Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS
THE CNTRL/SRN HIGH PLAINS...AND THE SRN PLAINS INTO PARTS OF THE LWR
MS VALLEY....
CORRECTED FOR 5% WIND/HAIL PROBABILITIES IN THE UPR MS VALLEY AREA.
...20Z UPDATE...
CATEGORICAL AND PROBABILISTIC OUTLOOKS HAVE BEEN ADJUSTED IN AN
ATTEMPT TO BETTER REFLECT STABILIZING TRENDS ACROSS THE EAST CENTRAL
PLAINS...IN THE WAKE OF CONVECTIVE CLUSTERS ADVANCING INTO THE OZARK
PLATEAU. THE MOST SIGNIFICANT DESTABILIZATION IS NOW FOCUSED ALONG
AN AXIS OF STRONGEST SURFACE HEATING ACROSS THE HIGH PLAINS...AND
SOUTH OF REMNANT OUTFLOW BOUNDARY NEAR THE SOUTHERN PLAINS RED
RIVER. WEAK SOUTHWESTERLY LOWER/MID TROPOSPHERIC FLOW CONTINUES TO
ADVECT WARM ELEVATED MIXED LAYER AIR EAST OF THE ROCKIES THROUGH
MUCH OF THE PLAINS...CONTRIBUTING TO STEEP MID-LEVEL LAPSE RATES.
AT THE SAME TIME...AN INCREASINGLY MOIST RETURN FLOW CONTINUES OFF
THE GULF INTO THE SOUTHERN PLAINS.
...CNTRL/SRN HIGH PLAINS INTO THE LOWER MS VALLEY...
THE SOUTHERN PLAINS MCS IS INTERCEPTING THE DEEP LAYER MOISTURE
RETURN...WHICH SHOULD BEGIN TO ADVECT TOWARD LOWER/MID PORTIONS OF
THE MISSISSIPI VALLEY AS 30-50 KT LOW-LEVEL FLOW ACROSS THE SOUTHERN
PLAINS VEERS TO A MORE SOUTHWESTERLY COMPONENT LATER THIS AFTERNOON
AND TONIGHT. THIS IS EXPECTED TO OCCUR AS A LOW AMPLITUDE SOUTHERN
STREAM TROUGH...WITH EMBEDDED IMPULSES... CONTINUES TO GRADUALLY
LIFT NORTHEAST OF THE SOUTHERN ROCKIES. THE ONGOING STORM CLUSTER
NEAR THE RED RIVER APPEARS TO BE ASSOCIATED WITH THE LEAD IMPULSE.
THIS ACTIVITY SHOULD SLOWLY DEVELOP EASTWARD ACROSS ARKANSAS LATE
THIS AFTERNOON...WHILE A NEW VIGOROUS STORM CLUSTER EVOLVES OVER
NORTHWEST/NORTH CENTRAL TEXAS...IN RESPONSE TO FORCING ASSOCIATED
WITH THE NEXT IMPULSE ALREADY IN THE PROCESS OF SPREADING ACROSS THE
TEXAS PANHANDLE/SOUTH PLAINS. AS INITIAL DISCRETE STORM DEVELOPMENT
GROWS UPSCALE...THE THREAT FOR DAMAGING WINDS MAY BECOME MOST
PROMINENT AS COLD POOLS CONSOLIDATE/ EXPAND AND STRENGTHEN ACROSS
NORTH TEXAS.
...NORTHERN PLAINS/UPPER MS VALLEY...
LATEST MODEL GUIDANCE CONTINUES TO SUGGEST SOMEWHAT LOW CONVECTIVE
POTENTIAL THROUGH THIS PERIOD. THIS APPEARS MAINLY DUE TO THE LACK
OF A MORE SUBSTANTIVE MOISTURE RETURN...AND LOW POTENTIAL FOR
APPRECIABLE BOUNDARY LAYER DESTABILIZATION. HOWEVER...AS AN INITIAL
IMPULSE EMERGES FROM THE ELONGATED CLOSED LOW PORTION OF THE UPPER
BLOCKING PATTERN...FORCING IN A LOW-LEVEL WARM ADVECTION REGIME
DOWNSTREAM OF A DEVELOPING SURFACE WAVE OVER NORTH DAKOTA PROBABLY
WILL BECOME SUPPORTIVE OF SCATTERED STORM DEVELOPMENT.
AND...ELEVATED DESTABILIZATION MAY BECOME SUFFICIENT TO CONTRIBUTE
TO THE RISK FOR LARGE HAIL IN A COUPLE OF THESE STORMS.
..KERR.. 04/29/2009
.PREV DISCUSSION... /ISSUED 1118 AM CDT WED APR 29 2009/
...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.
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