SWODY1
SPC AC 281957
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0257 PM CDT SUN JUN 28 2009
VALID 282000Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN KY/CENTRAL
APPALACHIANS SWD INTO THE CENTRAL GULF COAST AND SERN STATES...
...TN VALLEY...CENTRAL/SOUTHERN APPALACHIANS AND SERN STATES...
EARLY AFTERNOON SURFACE ANALYSIS INDICATED A COLD FRONT EXTENDED
FROM THE UPPER OH VALLEY SWWD THROUGH ERN KY TO NRN MS TO SRN AR.
THIS FRONT IN ADDITION TO ANOTHER COLD FRONT EXTENDING NWWD THROUGH
GA AND SEA BREEZE BOUNDARIES WILL REMAIN FOCI FOR ADDITIONAL TSTM
DEVELOPMENT INTO THE EVENING. PER PREVIOUS FORECAST...STRONG
SURFACE HEATING WITHIN A VERY MOIST AIR MASS HAS RESULTED IN VERY
STRONG INSTABILITY /MLCAPE 2500-3000 J/KG/ ACROSS MUCH OF THIS
REGION. DESPITE GENERALLY WEAK DEEP LAYER SHEAR...THE DEGREE OF
AVAILABLE INSTABILITY/MOISTURE LADEN AIR MASS WILL SUPPORT MAINLY
WET MICROBURSTS ACROSS MS/AL/GA/ERN TN INTO FAR NRN FL AS THE
PRIMARY SEVERE WEATHER THREAT. GIVEN GREATER STORM COVERAGE
UNDERWAY FARTHER WWD INTO MS AND SWD ACROSS SRN GA...THE CATEGORICAL
SLIGHT RISK AND ASSOCIATED SEVERE PROBABILITIES HAVE BEEN ADJUSTED
FOR THESE ADDITIONAL THREAT AREAS.
FARTHER NE INTO ERN KY/SRN WV/SWRN VA...INSTABILITY IS WEAKER WITH
THE NEWD EXTENT OF THE SLIGHT RISK AREA...BUT STRONGER EFFECTIVE
BULK SHEAR SUGGESTS A FEW ORGANIZED STORMS WILL BE POSSIBLE INTO THE
EARLY EVENING. A MORE STABLE AIR MASS LOCATED EAST OF THE CENTRAL
AND SRN APPALACHIANS SHOULD LIMIT THE AREAL EXTENT/THREAT AREA OF
THE ONGOING STORMS AS THE COLD FRONT ADVANCES EWD INTO THE HIGHER
TERRAIN.
...SW TX/EDWARDS PLATEAU TO ARKLATEX REGION...
LOW SEVERE WIND/HAIL PROBABILITIES HAVE BEEN EXTENDED SWWD FROM NRN
TX INTO SW TX. WATER VAPOR IMAGERY INDICATED A WEAK WWD MOVING
IMPULSE/PERTURBATION OVER THE EDWARDS PLATEAU WITH SLIGHTLY COOLER
MID LEVEL TEMPERATURES /-6 C AT 500 MB/ AS COMPARED TO VALUES
FARTHER ENE OVER NRN TX TO LA. TSTMS HAVE ALREADY FORMED ACROSS THE
EDWARDS PLATEAU/SW TX WITHIN A MODERATELY UNSTABLE AIR MASS. WEAK
DEEP LAYER SHEAR WILL PRECLUDE AN ORGANIZED SEVERE THREAT...BUT
SURFACE TEMPERATURE/DEWPOINT SPREADS AROUND 30 DEGREES WILL SUPPORT
LOCALLY STRONG WIND GUSTS.
..PETERS.. 06/28/2009
.PREV DISCUSSION... /ISSUED 1117 AM CDT SUN JUN 28 2009/
...TN VALLEY AND CENTRAL/SOUTHERN APPALACHIANS...
A COLD FRONT IS SAGGING SOUTHWARD ACROSS KY/TN...AS AN UPPER TROUGH
ROTATES ACROSS THE GREAT LAKES AND THE OH VALLEY. RATHER STRONG
HEATING AHEAD OF THE FRONT WILL LIKELY RESULT IN SCATTERED
THUNDERSTORMS FROM PARTS OF WV SOUTHWESTWARD INTO KY/TN. THESE
STORMS SHOULD SPREAD SOUTHEASTWARD INTO THE CENTRAL/SOUTHERN
APPALACHIANS THROUGH THE AFTERNOON AND EARLY EVENING. LARGE MLCAPE
VALUES OF 3000-4000 J/KG AND SUFFICIENT NORTHWEST FLOW ALOFT SUGGEST
THE STRONGEST STORMS WILL BE CAPABLE OF LOCALLY DAMAGING WINDS.
FARTHER SOUTHWEST ALONG THE FRONT FROM WEST TN INTO MS/AR...COVERAGE
OF INTENSE CONVECTION IS MORE UNCERTAIN. NEVERTHELESS...ISOLATED
PULSE OR WEAK MULTICELL STORMS ARE POSSIBLE WITH A RISK OF GUSTY
WINDS.
...AL/GA/FL...
MODELS ARE IN GOOD AGREEMENT THAT SCATTERED THUNDERSTORMS WILL FORM
THIS AFTERNOON ALONG AN AXIS ACROSS SOUTHERN GA/AL. FULL SUNSHINE
IN THIS AREA COMBINED WITH DEWPOINTS IN THE MID 70S WILL YIELD
STRONG INSTABILITY DESPITE WARM TEMPERATURES ALOFT. HIGH PWAT
VALUES AND MLCAPE OVER 3500 J/KG SUGGEST THAT A FEW OF THE STRONGER
STORMS COULD RESULT IN WET MICROBURSTS OVER THIS REGION LATER TODAY.
THREAT MAY ALSO EXTEND SOUTHWARD ALONG THE EAST COAST OF FL WHERE
SEA BREEZE CONVERGENCE WILL BE MAXIMIZED.
...CO...
A PLUME OF SUBTROPICAL MOISTURE IS EVIDENT ON WATER VAPOR IMAGERY
EXTENDING FROM AZ/NM INTO THE CENTRAL PLAINS. STRONG HEATING ON THE
NORTHERN EDGE OF THIS PLUME WILL HELP DESTABILIZE THE MOUNTAINS OF
CENTRAL CO...LEADING TO SCATTERED THUNDERSTORMS. THIS ACTIVITY WILL
SPREAD EASTWARD INTO THE PLAINS OF EASTERN CO DURING THE EVENING.
ISOLATED STORMS IN THIS REGION MAY PRODUCE STRONG/DAMAGING WINDS.
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