Monday, August 24, 2009

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 240541
SWODY1
SPC AC 240539

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT MON AUG 24 2009

VALID 241200Z - 251200Z

...NO SVR TSTM AREAS FORECAST...

...NRN PLAINS AND CNTRL PLAINS...
AN UPPER-LEVEL RIDGE IN THE UPPER-MS VALLEY WILL MOVE QUICKLY EWD
TODAY INTO THE GREAT LAKES REGION AS A LOW-AMPLITUDE SHORTWAVE
TROUGH MOVES INTO THE NRN PLAINS. AT THE SFC...A WELL-DEVELOPED LOW
WILL MOVE ENEWD ACROSS ND WITH A TRAILING COLD FRONT ADVANCING ESEWD
INTO THE DAKOTAS AND NEB. A STRONG CAPPING INVERSION WILL WEAKEN
ACROSS THE REGION THIS AFTERNOON ALLOWING FOR THUNDERSTORM
INITIATION ALONG THE COLD FRONT FROM NRN MN SWWD INTO ERN SD AND
CNTRL NEB. OTHER STORMS SHOULD INITIATE IN THE HIGHER TERRAIN OF SE
WY AND MOVE EWD INTO THE CNTRL HIGH PLAINS.

FORECAST SOUNDINGS ALONG THE ZONE OF EXPECTED INITIATION AT 21Z SHOW
ABOUT 25 KT OF 0-6 KM SHEAR DUE MOSTLY TO DIRECTIONAL SHEAR BELOW
700 MB. THIS SUGGESTS STORM STRUCTURES WILL REMAIN MULTICELL AND
SOMEWHAT DISORGANIZED. AS THE COLD FRONT APPROACHES THE ERN
DAKOTAS...FORECAST SOUNDINGS VEER WINDS AT THE LOW-LEVELS MAKING THE
SHEAR SLIGHTLY LESS FAVORABLE WITH TIME DURING THE EARLY EVENING.
FOR THIS REASON...WILL ONLY FORECAST MARGINALLY SEVERE CONVECTION IN
THE NRN PLAINS WITH HAIL AND ISOLATED DAMAGING WIND GUSTS THE MAIN
SEVERE THREATS.

FURTHER SOUTHWEST IN SE WY AND WRN NEB...VERTICAL SHEAR IS FORECAST
TO BE STRONGER THIS AFTERNOON DUE TO SPEED SHEAR IN THE MID-LEVELS.
THIS COULD SUPPORT A FEW ROTATING STORMS. HOWEVER...WEAK INSTABILITY
SHOULD MAKE ANY SEVERE THREAT VERY ISOLATED WITH HAIL THE MAIN
THREAT.

...SE TX...
ONSHORE FLOW WILL CONTINUE TODAY REINFORCING A NARROW MOIST AXIS
WITH SFC DEWPOINTS IN THE LOWER TO MID 70S F EXTENDING NWWD FROM THE
UPPER TX COAST INTO ECNTRL TX. MODERATE TO STRONG INSTABILITY SHOULD
AGAIN BE IN PLACE TODAY ALONG THE MOIST AXIS WITH SCATTERED
THUNDERSTORMS INITIATING THIS AFTERNOON. FORECAST SOUNDINGS IN
ECNTRL TX AT 21Z SHOW VERY STEEP LOW-LEVEL LAPSE RATES WHICH SHOULD
BE FAVORABLE FOR MARGINALLY SEVERE STORMS CAPABLE OF PRODUCING
STRONG WIND GUSTS ESPECIALLY WHERE STRONG INSTABILITY IS PRESENT.

..BROYLES/SMITH.. 08/24/2009

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