DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211548
SWODY1
SPC AC 211545

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1045 AM CDT THU AUG 21 2008

VALID 211630Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF NORTHEAST FL
AND SOUTHEAST GA...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF MT/ND...

...MT...
MORNING WATER VAPOR IMAGERY SHOWS POWERFUL MID/UPPER LEVEL JET MAX
SURGING EASTWARD ACROSS THE PACIFIC NORTHWEST. THIS FEATURE WILL
NOSE INTO MT THIS AFTERNOON...THEN ACROSS THE NORTHERN PLAINS
TONIGHT. THE AIRMASS IN PLACE OVER MUCH OF MT IS RATHER DRY AND
ONLY MARGINALLY UNSTABLE. HOWEVER...STRONG DAYTIME HEATING WILL
RESULT IN A DEEP MIXED BOUNDARY LAYER BY MID AFTERNOON AND MLCAPE
VALUES OF AROUND 500 J/KG AND LITTLE CAP. PRESENT INDICATIONS ARE
THAT LOW LEVEL FORCING ALONG COLD FRONT SURGING EASTWARD ACROSS MT
WILL HELP TO INITIATE SCATTERED THUNDERSTORMS BY MID AFTERNOON OVER
CENTRAL MT. THESE STORMS MAY BECOME ORGANIZED INTO A LINEAR MCS AND
SURGE EASTWARD ACROSS MT AND INTO ND DURING THE EVENING. STEEP LOW
LEVEL LAPSE RATES AND STRENGTHENING LOW LEVEL WINDS NEAR/BEHIND
FRONT WILL PROMOTE A RISK OF LOCALLY DAMAGING WINDS.

...ND...
MORNING U/A ANALYSIS SHOWS SOUTHERLY LOW LEVEL JET ACROSS THE
NORTHERN PLAINS. THIS JET IS EXPECTED TO BUILD SLIGHTLY WESTWARD
AND BACK THIS AFTERNOON OVER ND AS UPPER TROUGH APPROACHES FROM THE
WEST. THIS WILL ENHANCE LOW LEVEL WARM ADVECTION AND LIKELY LEAD TO
SCATTERED THUNDERSTORMS OVER PARTS OF ND. MLCAPE VALUES OF UP TO
1500 J/KG...COUPLED WITH EFFECTIVE SHEAR VALUES OF 30-35 KNOTS
SUGGEST A RISK OF ISOLATED SUPERCELLS CAPABLE OF LARGE HAIL AND
DAMAGING WINDS. LATER THIS EVENING/TONIGHT...FAST MOVING LINE OF
STORMS IS EXPECTED TO MOVE OUT OF MT INTO ND POSING ANOTHER RISK OF
DAMAGING WINDS AND HAIL.

...FL/GA...
TROPICAL STORM FAY REMAINS ALONG THE EAST COAST OF FL TODAY...AND IS
EXPECTED TO BEGIN MOVING SLOWLY WEST-NORTHWESTWARD DURING THE
PERIOD. SO FAR...VERTICAL SHEAR AND CONVECTIVE CHARACTER HAVE NOT
BEEN PARTICULARLY FAVORABLE FOR SUPERCELLS/TORNADOES OVER NORTHEAST
FL OR SOUTHEAST GA. IT APPEARS AREA OF STRONGEST LOW LEVEL SHEAR
AND MORE CELLULAR CONVECTION HAS REMAINED OFF THE FL COAST.
HOWEVER...AS SYSTEM BEGINS TO DRIFT WESTWARD...THIS AREA OF ENHANCED
SHEAR MAY MOVE INLAND WITH A RISK OF ISOLATED TORNADOES.

...TX...
A FEW WET MICROBURSTS APPEAR POSSIBLE LATER THIS AFTERNOON OVER
PARTS OF EAST TX...IN REGION OF AMPLE LOW LEVEL MOISTURE...STRONG
INSTABILITY...DRY AIR ALOFT...BUT WEAK VERTICAL SHEAR. ORGANIZED
SEVERE STORMS ARE NOT ANTICIPATED AT THIS TIME.

..HART/HURLBUT.. 08/21/2008

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