SWODY1
SPC AC 191949
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0149 PM CST WED DEC 19 2007
VALID 192000Z - 201200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS EAST TX INTO
WESTERN/CENTRAL LA AND SW AR...
..TX/LA/SW AR...
PROGRESSIVE UPPER TROUGH NOW OVER ERN AZ/WRN NM IS FORECAST TO TRACK
EWD AND BEGIN AFFECTING THE SRN PLAINS LATER THIS AFTERNOON AND
EVENING. IN ADVANCE OF THIS FEATURE...LOW LEVEL WINDS OVER EAST TX/
LA WILL BACK TO A MORE SLY COMPONENT AND SLOWLY STRENGTHEN WITH
ADDITIONAL INFLUX OF GULF MOISTURE. THIS COMBINED WITH STEEPENING
LAPSE RATES ATTENDANT TO APPROACH OF UPPER TROUGH WILL ESTABLISH A
MARGINALLY UNSTABLE AIRMASS ACROSS THE AREA. BY EVENING...SURFACE
DEWPOINTS IN THE MID 60S ARE LIKELY ACROSS MUCH OF SOUTHEAST TX AND
SOUTHWEST LA. INCREASING LARGE SCALE ASCENT AND COOLING ASSOCIATED
WITH UPPER TROUGH WILL LIKELY YIELD MUCAPE VALUES OF 500-1000 J/KG
OVER MUCH OF EAST TX AND WESTERN LA AFTER 06Z.
EARLY AFTERNOON MESOSCALE ANALYSES AND REGIONAL RADARS SHOWED
SHALLOW CONVECTION FROM VICINITY OF HOU NEWD INTO SE TX DEVELOPING
WITHIN MARGINALLY UNSTABLE AIR MASS /MLCAPE 250-500 J/KG/. UPPER
RIDGE OVER THIS REGION THIS AFTERNOON IS EXPECTED TO INHIBIT DEEP
CONVECTION FROM OCCURRING UNTIL LATER IN THE FORECAST PERIOD.
PRESENT INDICATIONS CONTINUE TO SUGGEST THAT INCREASING LOW LEVEL
WARM ADVECTION WILL HELP INITIATE SCATTERED TSTMS AROUND MIDNIGHT
ACROSS PARTS OF EAST TX...SPREADING ACROSS LA THROUGH THE MORNING
HOURS. FORECAST SOUNDINGS SHOW A SUFFICIENT COMBINATION OF ELEVATED
CAPE...MID LEVEL LAPSE RATES...AND DEEP LAYER VERTICAL SHEAR FOR A
RISK OF EMBEDDED SUPERCELLS CAPABLE OF LARGE HAIL AND DAMAGING
WINDS. BY LATE IN THE PERIOD...LOW LEVEL WINDS WILL STRENGTHEN
SUFFICIENTLY TO ALSO POSE A RISK OF TORNADOES IN THOSE STORMS THAT
ARE SURFACE-BASED.
.PETERS.. 12/19/2007
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