SWOD48
SPC AC 270900
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0400 AM CDT SUN SEP 27 2009
VALID 301200Z - 051200Z
...SEVERE STORMS POSSIBLE ACROSS THE CNTRL PLAINS INTO THE LWR MO
VALLEY/OZARK PLATEAU REGION THURSDAY INTO EARLY FRIDAY...
MEDIUM RANGE FORECAST GUIDANCE APPEARS TO BE COMING MORE SIMILAR
CONCERNING THE EVOLUTION OF A SIGNIFICANT POLAR SHORT WAVE IMPULSE
WHICH IS PROGGED INTO THE GREAT BASIN BY EARLY WEDNESDAY. THE
27/00Z ECMWF AND GFS ARE BOTH SUGGESTIVE THAT THIS FEATURE WILL
REMAIN PROGRESSIVE AS IT INTERACTS WITH A STRENGTHENING BELT OF FLOW
EMANATING FROM THE LOWER LATITUDE EASTERN PACIFIC. AN INCREASING
NEGATIVE TILT ORIENTATION IS PROGGED AS IT ADVANCES EAST OF THE
CENTRAL ROCKIES ON THURSDAY...UNDERCUTTING A BLOCKING RIDGE
DEVELOPING TO THE NORTH OF THE GREAT LAKES REGION. STRONG FORCING
FOR UPWARD VERTICAL MOTION...DIFFERENTIAL THERMAL ADVECTION AND GULF
MOISTURE RETURN ARE EXPECTED TO CONTRIBUTE TO WEAK TO MODERATE
POTENTIAL INSTABILITY AND WIDESPREAD CONVECTIVE DEVELOPMENT IN THE
PRESENCE OF STRONG SHEAR. THIS APPEARS MOST LIKELY ACROSS THE
CENTRAL PLAINS INTO THE LOWER MISSOURI VALLEY AND OZARK PLATEAU
REGION...WHERE AN OUTBREAK OF SEVERE STORMS APPEARS POSSIBLE
THURSDAY INTO EARLY FRIDAY. THEREAFTER... BLOCKING/SPLIT UPPER FLOW
PATTERN EVOLUTION BECOMES MORE UNCLEAR. COUPLED WITH UNCERTAIN
NEGATIVE FEEDBACK FROM PRIOR CONVECTIVE ACTIVITY...PREDICTABILITY OF
POSSIBLE ADDITIONAL SEVERE STORM POTENTIAL ACROSS THE
CENTRAL/EASTERN STATES BECOMES LOW.
..KERR.. 09/27/2009
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