SPC AC 271948
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0248 PM CDT WED MAY 27 2009
VALID 272000Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN/EVE ACROSS PARTS
OF THE MS AND OH VALLEYS....
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN/EVE ACROSS PARTS
OF THE LOWER RIO GRANDE VALLEY....
...20Z UPDATE...
SEVERE POTENTIAL APPEARS TO HAVE LOWERED ACROSS MUCH OF WESTERN GULF
COAST/LOWER MISSISSIPPI VALLEY REGION...DUE TO THE STABILIZING
INFLUENCE OF THE LARGE CONVECTIVE COMPLEX AND ASSOCIATED SURFACE
COLD POOL WHICH CONTINUE TO ADVANCE SOUTHEAST OF TEXAS COASTAL
AREAS. IT IS NOT CLEAR HOW MUCH LONGER THE CONVECTIVE SYSTEM WILL
PERSIST...AS POSSIBLE SUPPORTING FORCING ASSOCIATED WITH A MID/HIGH
LEVEL SPEED MAXIMUM LIFTS INTO THE OZARK PLATEAU THIS AFTERNOON.
ALTHOUGH STRONG/SEVERE STORM DEVELOPMENT IS STILL A POSSIBILITY
ALONG A TRAILING OUTFLOW BOUNDARY ADVANCING INTO THE BROWNSVILLE/
LAREDO AREA OF THE LOWER RIO GRANDE VALLEY...MID/UPPER FORCING
APPEARS NON-EXISTENT...AND MID-LEVEL INHIBITION MAY REMAIN AN ISSUE
THIS AFTERNOON. PRIMARY CONVECTIVE POTENTIAL THROUGH THE REMAINDER
OF THE AFTERNOON AND EVENING NOW SEEMS LIKELY TO BECOME FOCUSED IN
THE SOUTHEASTERLY LOW-LEVEL UPSLOPE FLOW REGIME ACROSS THE HIGHER
TERRAIN OF MEXICO.
COUPLING OF THE UPPER-LEVEL JET STREAK LIFTING INTO THE OZARK
PLATEAU...WITH ANOTHER MIGRATING THROUGH THE UPPER GREAT LAKES
REGION...MAY PROVIDE FORCING TO ENHANCE CONVECTIVE DEVELOPMENT
WITHIN A PRE-FRONTAL INSTABILITY AXIS FROM UPPER PORTIONS OF THE
LOWER MISSISSIPPI VALLEY INTO THE LOWER OHIO VALLEY LATE THIS
AFTERNOON AND EVENING. LATEST RUC ANALYSIS SUGGESTS MIXED LAYER
CAPE IS ON THE ORDER OF 2000-3000 J/KG ACROSS THIS REGION...AND
THERE DOES APPEAR POTENTIAL FOR CONSOLIDATION OF INTENSIFYING STORMS
AND ASSOCIATED COLD POOLS INTO A GROWING STORM CLUSTER. SHEAR IS
GENERALLY WEAK...BUT IF THIS OCCURS...MOMENTUM ASSOCIATED WITH 20 KT
DEEP LAYER MEAN WEST SOUTHWESTERLY FLOW MAY BE ENOUGH TO CONTRIBUTE
TO A RISK FOR POTENTIALLY DAMAGING WIND GUSTS AT LEAST APPROACHING
SEVERE LIMITS.
..KERR.. 05/27/2009
.PREV DISCUSSION... /ISSUED 1052 AM CDT WED MAY 27 2009/
MORNING U/A ANALYSIS SHOWS BROAD CYCLONIC FLOW ALOFT ACROSS THE
SOUTHERN PLAINS AND LOWER/MID MS VALLEY...WITH 500MB WIND SPEEDS
GENERALLY AOB 30 KNOTS. A SURFACE COLD FRONT HAS PUSHED SOUTHWARD
THROUGH OK AND INTO CENTRAL TX...LEAVING AN ARC OF MOIST/UNSTABLE
AIR FROM SOUTH TX INTO LA...THEN NORTHWARD INTO IL/IND. THESE
REGIONS WILL BE THE THREAT AREA FOR STRONG/SEVERE STORMS TODAY.
...SOUTH TX...
INTENSE THUNDERSTORMS ARE CURRENTLY OCCURRING ALONG A SAGGING
SURFACE BOUNDARY NORTH OF CRP. THIS ACTIVITY WILL MOVE OFFSHORE
EARLY THIS AFTERNOON...LEAVING AN EXTREMELY UNSTABLE AIRMASS ACROSS
DEEP SOUTH TX. FORECAST SOUNDINGS ALONG AND SOUTH OF THE BOUNDARY
INDICATE A RATHER WEAK CAP AND THE RISK OF REDEVELOPMENT OF
SCATTERED CONVECTION DURING PEAK HEATING. STORMS MAY INITIALLY FORM
OVER THE MOUNTAINS OF MEXICO AND SPREAD EASTWARD TOWARD THE
LRD/CRP/BRO AREAS. DEEP LAYER VERTICAL SHEAR PROFILES WOULD FAVOR
SUPERCELL STORM STRUCTURES WITH A RISK OF VERY LARGE HAIL AND
DAMAGING WINDS IF THIS SCENARIO UNFOLDS.
OTHER STORMS MAY DEVELOP THIS AFTERNOON AND EVENING OVER PARTS OF
SOUTHWEST TX AND PROPAGATE SOUTHEASTWARD DOWN THE RIO GRANDE VALLEY
OVERNIGHT. THESE STORMS COULD ORGANIZE INTO AN MCS WITH A RISK OF
ISOLATED SEVERE STORMS.
...LOWER MS VALLEY...
AMPLE MOISTURE AND INSTABILITY ARE PRESENT THIS MORNING OVER MUCH OF
THE LOWER MS VALLEY WITH DEWPOINTS IN THE UPPER 60S TO LOWER 70S.
RELATIVELY STRONG DAYTIME HEATING WILL LEAD TO A STRONGLY UNSTABLE
AIRMASS BY AFTERNOON WITH MLCAPE VALUES OVER 3000 J/KG. VERTICAL
SHEAR IS WEAK...AND LARGE SCALE FORCING MECHANISMS ARE HARD TO
IDENTIFY. NEVERTHELESS...IT APPEARS LIKELY THAT AT LEAST SCATTERED
THUNDERSTORMS WILL DEVELOP ALONG THIS CORRIDOR WITH A RISK OF HAIL
AND DAMAGING WINDS IN THE STRONGER CORES.
...MID MS VALLEY...
VISIBLE SATELLITE IMAGERY SHOWS GENERALLY CLEAR SKIES OVER SOUTHEAST
MO/SOUTHERN IL. THIS AREA WILL ALSO BECOME QUITE UNSTABLE BY
AFTERNOON WITH MLCAPE OVER 3000 J/KG AND LITTLE CAP. SCATTERED
THUNDERSTORMS ARE EXPECTED TO DEVELOP BY EARLY AFTERNOON OVER MO AND
SPREAD EASTWARD INTO PARTS OF IL/IND/KY BY EVENING. THIS REGION MAY
EXPERIENCE SLIGHTLY STRONGER LARGE SCALE FORCING AS REMNANT
CIRCULATIONS FROM OVERNIGHT CONVECTION OVERSPREAD THE AREA. THIS
MAY IN TURN HELP FOCUS STORMS AND LEAD TO WIDELY SCATTERED SEVERE
STORMS.
...FL...
SCATTERED STRONG STORMS WITH A RISK OF WET MICROBURSTS AND HAIL WILL
BE POSSIBLE ONCE AGAIN OVER THE CENTRAL AND SOUTHERN FL PENINSULA
THIS AFTERNOON. NORTH FL IS IN THE WAKE OF A MID LEVEL SHORTWAVE
TROUGH...AND MAY SEE LOWER COVERAGE OF STORMS THAN THE LAST FEW
DAYS.
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