SPC AC 261246
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0746 AM CDT TUE MAY 26 2009
VALID 261300Z - 271200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A RATHER DIFFUSE AND COMPLEX PATTERN PERSISTS ACROSS THE CONUS
BETWEEN THE PRIMARY NRN STREAM JET OVER SRN CANADA AND A WEAKER
SUBTROPICAL JET FROM NRN MEXICO INTO THE GULF OF MEXICO. THE
REMNANTS OF THE WARM CORE LOW OVER MO WILL MOVE NNEWD TOWARD NRN
IL/ERN IA TODAY WHILE GRADUALLY PHASING WITH A SEPARATE MID LEVEL
TROUGH THAT IS MOVING SLOWLY EWD OVER THE CENTRAL PLAINS. AT THE
SURFACE...THE MO CYCLONE WILL MOVE NEWD TOWARD LAKE MI WHILE A
SECONDARY/WEAKER LOW PROGRESSES ENEWD FROM NW TX ACROSS
OK...FOLLOWED BY THE SEWD MOVEMENT OF A COLD FRONT ACROSS MUCH OF
OK/NW TX BY EARLY WEDNESDAY. A BROAD AREA FROM THE CENTRAL/SRN
ROCKIES EWD ACROSS THE SRN PLAINS TO THE MS VALLEY AND SE ATLANTIC
COAST WILL EXPERIENCE WIDELY-SCATTERED TO SCATTERED THUNDERSTORMS
TODAY THROUGH TONIGHT.
...CENTRAL/S TX THROUGH TONIGHT...
A LARGE COLD POOL HAS BEEN PRODUCED BY A CLUSTER OF STRONG STORMS
THAT IS MOVING OFF THE TX COAST NEAR CRP. OTHER UPSTREAM STORMS
CONTINUE TO DEVELOP OVER THE RIO GRANDE VALLEY AND EXTREME NE
MEXICO...AND SOME FORM OF THIS CONVECTION WILL LIKELY CONTINUE TO
IMPACT S TX THROUGH THE DAY IN ADVANCE OF A SPEED MAX MOVING EWD
OVER NRN MEXICO. THE OPERATIONAL AND HIGH-RES MODELS HAVE STRUGGLED
TO REPRESENT THE OVERNIGHT CONVECTION...THUS WILL BASE THIS FORECAST
LARGELY ON EXTRAPOLATION OF THE ONGOING RIO GRANDE STORMS ALONG AND
JUST N OF THE OUTFLOW BOUNDARY THAT IS STILL MOVING SWD INTO DEEP S
TX.
VERTICAL SHEAR OVER S TX IS FAVORABLE FOR SUPERCELLS WITH EFFECTIVE
BULK WIND DIFFERENCES OF 40-50 KT BENEATH 50-60 KT WLY FLOW AROUND
300 MB...AND CLOCKWISE CURVATURE OF THE HODOGRAPHS WILL FAVOR
RIGHT-MOVING SUPERCELLS. MEANWHILE...THE 12Z BRO SOUNDING IS
STRONGLY UNSTABLE WHEN MODIFIED FOR AFTERNOON TEMPERATURES IN THE
90S. HOWEVER...THE EARLY CONVECTION/OUTFLOW HAVE COMPLICATED THE
SITUATION AND CONFIDENCE IS NOT PARTICULARLY HIGH IN HOW CONVECTION
WILL EVOLVE LATER TODAY. WILL MAINTAIN 5% HAIL/WIND
PROBABILITIES...BUT THERE IS STILL SOME POTENTIAL FOR A SMALL SLIGHT
RISK UPGRADE FOR S TX LATER TODAY.
...OK/NW TX THROUGH TONIGHT...
A COMPLEX SCENARIO IS UNFOLDING THIS MORNING WITH AN ONGOING
THUNDERSTORM CLUSTER ACROSS SRN OK. THESE STORMS HAVE PRODUCED A
COLD POOL THAT IS OVERSPREADING MUCH OF CENTRAL/SRN OK AND EXTREME
NW/N CENTRAL TX...THOUGH THE CLUSTER WILL LIKELY WEAKEN DURING THE
MORNING AS THE LLJ AND WAA ABOVE THE COLD POOL LIKEWISE DIMINISH.
UNCERTAINTY FOR THIS AFTERNOON/EVENING CENTERS ON THE LINGERING
IMPACTS OF THE COLD POOL AND THE RATE OF RECOVERY/DESTABILIZATION IN
ADVANCE OF THE SEWD MOVING COLD FRONT ACROSS NW OK INTO NW TX. THE
LACK OF CLOUD COVER SHOULD ALLOW SUBSTANTIAL DAYTIME HEATING IN THE
WAKE OF THE MORNING CONVECTION...AND SUFFICIENT INSTABILITY /MLCAPE
VALUES OF 1000-1500 J/KG BASED ON SURFACE TEMPERATURES IN THE 80S
AND DEW POINTS OF 55-60 F/ TO SUPPORT THUNDERSTORM DEVELOPMENT ALONG
THE COLD FRONT...AND POTENTIALLY THE REMNANT OUTFLOW BOUNDARY.
DEEP LAYER VERTICAL SHEAR WILL BE STRONGER THAN PREVIOUS DAYS AS A
RESULT OF 25-30 KT WLY MID LEVEL FLOW... AND A 50-70 KT SPEED MAX
OBSERVED AT JTN/AMA AROUND 10 KM AGL THAT IS FORECAST TO TRANSLATE
NEWD OVER OK THIS AFTERNOON. STILL...FORECAST HODOGRAPHS ARE FAR
FROM CLASSIC WITH RELATIVELY WEAK LOW-LEVEL SHEAR AND A PRONOUNCED
TENDENCY FOR BACKING WITH HEIGHT. THE NET RESULT COULD BE SOME
RATHER UNUSUAL/TRANSIENT SUPERCELL CONFIGURATIONS...OR JUST
PRIMARILY MULTICELL CLUSTERS AND LINE SEGMENTS ALONG THE FRONT.
GIVEN THE MAGNITUDE OF THE BULK SHEAR AND INSTABILITY...A FEW STORMS
SHOULD BE CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WINDS.
BUT...THE MULTIPLE COMPLEXITIES IN THE FORECAST ALSO ARGUE FOR
MAINTAINING ONLY LOW HAIL/WIND PROBABILITIES IN THIS UPDATE.
...NE MO/SE IA/NW IL TODAY...
THE REMNANTS OF THE WARM CORE LOW WILL DRIFT NNEWD FROM MO. THOUGH
LOW-LEVEL FLOW AND INSTABILITY ARE SOMEWHAT WEAKER COMPARED TO
PREVIOUS DAYS FARTHER TO THE S...VERY MOIST PROFILES AND SOMEWHAT
ENHANCED LOW-LEVEL SHEAR ALONG THE SURFACE WARM FRONT COULD SUPPORT
SOME ROTATION AND THE POSSIBILITY OF A BRIEF/WEAK TORNADO.
...FL TODAY...
ANOTHER DAY OF ACTIVE SEA BREEZE CONVECTION IS EXPECTED...WITH WEAK
MEAN WLY FLOW FAVORING THE E COAST SEA BREEZE THIS AFTERNOON.
AFTERNOON MLCAPE VALUES AROUND 2000 J/KG AND SEASONALLY COOL MID
LEVEL TEMPERATURES WILL AGAIN SUPPORT A THREAT FOR ISOLATED HAIL AND
WET MICROBURSTS.
..THOMPSON/SMITH.. 05/26/2009
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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