SWODY1
SPC AC 271325
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0825 AM CDT WED MAY 27 2009
VALID 271300Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS TODAY INTO EARLY TONIGHT FROM
THE MID MS VALLEY SWD AND SWWD INTO S TX...
CORRECTED FOR GRAPHIC CODING PROBLEMS
...SYNOPSIS...
A BROAD/WEAK MID LEVEL TROUGH...WITH SEVERAL EMBEDDED SPEED
MAXIMA...WILL MOVE SLOWLY EWD FROM THE PLAINS TO THE MS VALLEY. THE
MID LEVEL TROUGH WILL BE ACCOMPANIED BY A SURFACE CYCLONE WHICH WILL
PROGRESS ENEWD FROM NW IL TO LOWER MI...WHILE A TRAILING COLD FRONT
MOVES EWD TO THE MS RIVER AND SWD INTO S TX. A MARITIME TROPICAL
BOUNDARY LAYER AND HIGH PW ENVIRONMENT IS PRESENT IN ADVANCE OF THE
COLD FRONT ACROSS THE NW GULF COAST...MS VALLEY...AND SE ATLANTIC
STATES. THIS MOIST ENVIRONMENT...ALONG WITH DAYTIME HEATING...WILL
PROMOTE SCATTERED THUNDERSTORM DEVELOPMENT ACROSS THE WARM SECTOR.
THE MORE INTENSE STORMS WILL BE FOCUSED ALONG THE COLD FRONT THROUGH
THIS EVENING FROM TX INTO THE MID MS VALLEY.
...S TX TODAY INTO EARLY TONIGHT...
AN OUTFLOW BOUNDARY IS MOVING SWD INTO S CENTRAL AND SE TX IN
ADVANCE OF THE SURFACE COLD FRONT. MEANWHILE...WEAK SPEED MAXIMA
ARE PROGRESSING EWD OVER THE RIO GRANDE VALLEY AND CENTRAL TX WITHIN
THE SUBTROPICAL JET...WHICH ARE CONTRIBUTING TO RENEWED THUNDERSTORM
DEVELOPMENT ACROSS CENTRAL/S CENTRAL TX THIS MORNING. THE 12Z
SOUNDINGS FROM CRP/BRO TO THE S OF THE OUTFLOW AND COLD FRONT SHOW
THE POTENTIAL FOR EXTREME INSTABILITY /MLCAPE VALUES IN EXCESS OF
4000 J/KG/ WITH SURFACE TEMPERATURES AOA 90 F AND LOW-MID 70S DEW
POINTS. IT APPEARS THAT THE DEVELOPING STORMS THIS MORNING MAY
PERSIST INTO THE DAY AND GRADUALLY INTENSIFY AS THE BOUNDARY LAYER
WARMS AND CONVECTIVE INHIBITION IS REDUCED...AND ADDITIONAL STORMS
COULD FORM UPSTREAM IN THE UPSLOPE REGION BACK TOWARD DRT...AND
ALONG THE SEA BREEZE THIS AFTERNOON.
THE COMBINATION OF SUBSTANTIAL DEEP LAYER BULK SHEAR BENEATH THE
SUBTROPICAL JET AND EXTREME INSTABILITY WILL SUPPORT A FEW ORGANIZED
SEVERE STORMS...INCLUDING PERSISTENT CLUSTERS AS WELL AS SUPERCELLS.
LARGE HAIL AND DAMAGING WINDS WILL BE PROBABLE WITH ANY SUSTAINED
STORMS. THE PRIMARY UNCERTAINTY IN THE SEVERE THREAT WILL BE THE
COVERAGE OF STORMS...THOUGH ENOUGH CONVECTION APPEARS PROBABLE TO
WARRANT AN UPGRADE TO SLIGHT RISK.
...MID MS VALLEY SWD/SWWD INTO S TX THROUGH LATE EVENING...
OVERNIGHT CONVECTION HAS WEAKENED THIS MORNING ACROSS THE
ARKLATEX...THOUGH A REMNANT OUTFLOW BOUNDARY HAS MOVED EWD INTO SW
AR/NW LA AND SEWD INTO E TX IN ADVANCE OF THE FRONT. WEAK ASCENT
ALONG THE OUTFLOW BOUNDARY AND DIFFERENTIAL HEATING IN CONJUNCTION
WITH THE LINGERING CLOUDS FROM OVERNIGHT CONVECTION WILL SUPPORT
ADDITIONAL THUNDERSTORM DEVELOPMENT DURING THE AFTERNOON. STORM
DEVELOPMENT MAY ALSO OCCUR ALONG THE SURFACE COLD FRONT IF THE
CLOUDS AND THE REMNANT OUTFLOW DISSIPATE. EITHER WAY...REGIONAL 12Z
SOUNDINGS SHOW THE POTENTIAL FOR STRONG INSTABILITY THIS AFTERNOON
/MLCAPE VALUES OF 2000-3000 J/KG/...AND THE POTENTIAL FOR INTENSE
UPDRAFTS. THOUGH SOME MODEST INCREASE IN MID-UPPER FLOW WILL OCCUR
TOWARD THE MS RIVER AS THE MID LEVEL TROUGH MOVES EWD...THE PRIMARY
SEVERE THREATS WILL BE DAMAGING OUTFLOW WINDS AND LARGE HAIL WITH
MULTICELL CLUSTERS THIS AFTERNOON INTO THIS EVENING.
FARTHER NE INTO THE OH VALLEY...INSTABILITY WILL BE SOMEWHAT WEAKER
COMPARED TO THE MIDDLE AND LOWER MS VALLEY...AND VERTICAL SHEAR WILL
REMAIN RELATIVELY WEAK. STILL..DAYTIME HEATING WILL SUPPORT THE
DEVELOPMENT OF SCATTERED THUNDERSTORMS...THE STRONGEST OF WHICH
COULD PRODUCE MARGINALLY SEVERE HAIL AND ISOLATED DOWNBURST WINDS.
...SRN AND ERN FL THIS AFTERNOON...
ANOTHER DAY OF DIURNAL...SEA BREEZE CONVECTION IS EXPECTED ACROSS
THE CENTRAL AND ERN FL PENINSULA. A MEAN WLY FLOW IN ASSOCIATION
WITH A SUBTROPICAL SHORTWAVE TROUGH WILL FAVOR THE E COAST SEA
BREEZE...AND THE STRONGER INSTABILITY SHOULD BE LOCATED OVER
CENTRAL/S FL TODAY. THE STRONGEST STORMS WILL BE CAPABLE OF
ISOLATED LARGE HAIL AND STRONG DOWNBURST WINDS.
..THOMPSON.. 05/27/2009
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