SWOD48
SPC AC 200934
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0434 AM CDT SUN APR 20 2008
VALID 231200Z - 281200Z
...DISCUSSION...
ECMWF AND GFS HAVE COME INTO REASONABLE AGREEMENT WITH EVOLUTION OF
LARGE SCALE PATTERN THROUGH ABOUT DAY 6. LOW AMPLITUDE PROGRESSIVE
PATTERN IS FORECAST MUCH OF THIS PERIOD WITH THE STRONGER MID-UPPER
FLOW EXPECTED TO REMAIN OVER THE NRN HALF OF THE COUNTRY. UPPER
TROUGH WILL ADVANCE THROUGH THE WRN U.S. DAY 4 WITH LEAD IMPULSE
REACHING THE CNTRL PLAINS TUESDAY NIGHT. POTENTIAL WILL ALSO EXIST
FOR WEAKER IMPULSES EMBEDDED IN SRN STREAM TO ADVANCE THROUGH TX.
A LEE TROUGH WILL DEEPEN OVER THE CNTRL HIGH PLAINS WITHIN ZONE OF
HEIGHT FALLS DOWNSTREAM FROM UPPER TROUGH. THIS WILL CONTRIBUTE TO
THE FRONT OVER THE SRN PLAINS LIFTING BACK NWD AS A WARM FRONT.
A FEW STORMS COULD DEVELOP OVER KS/OK ALONG OR NORTH THE RETREATING
FRONT DAY 4 AS WELL AS FARTHER SOUTH ALONG AND E OF DRYLINE ACROSS
TX. WITH FASTER UPPER FLOW LIKELY TO REMAIN NORTH OF WARM
SECTOR...OVERALL SHEAR PROFILES WILL NOT BE PARTICULARLY STRONG OVER
MUCH OF THIS REGION. HOWEVER...THE THERMODYNAMIC ENVIRONMENT MAY
SUPPORT THE POTENTIAL FOR A FEW STRONG TO SEVERE STORMS. OTHER
ELEVATED STORMS MAY DEVELOP WITHIN WARM ADVECTION REGIME OVER PARTS
OF THE NRN PLAINS.
THREAT FOR SEVERE STORMS WILL ALSO EXIST DAY 5 INTO DAY 6 FROM PARTS
OF THE CNTRL AND SRN PLAINS AND POSSIBLY THE UPPER MS VALLEY REGIONS
AS THE UPPER TROUGH EJECTS INTO THE PLAIN ACCOMPANIED BY A COLD
FRONT AND INCREASING VERTICAL SHEAR. NWD EXTENT OF THE THREAT WILL
DEPEND ON DEGREE OF LOW LEVEL MOISTURE RETURN.
A RISK AREA MAY BE INTRODUCED IN LATER OUTLOOKS TO INCLUDE DAY 4-6
MAINLY FOR PORTIONS OF THE PLAINS. HOWEVER...PREFER TO WAIT FOR
ANOTHER SET OF MODEL RUNS IN ORDER TO ASCERTAIN RUN TO RUN
CONSISTENCY.
..DIAL.. 04/20/2008
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