SWODY1
SPC AC 280522
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1222 AM CDT WED APR 28 2010
VALID 281200Z - 291200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MIDLEVEL VORTICITY MAXIMUM CURRENTLY MOVING THROUGH THE PACIFIC NW
WILL CONTINUE NEWD...EVENTUALLY FORMING A CLOSED MIDLEVEL
CIRCULATION OVER THE NRN HIGH PLAINS. THIS EVOLUTION WILL OCCUR IN
RESPONSE TO THE SEWD PROGRESSION OF THE NEXT MIDLEVEL JET STREAK
FROM THE ERN PACIFIC INTO THE LOWER CO VALLEY. THE NET EFFECT WILL
BE THE OVERALL DEEPENING/BROADENING OF WRN U.S. TROUGH.
IN THE LOW LEVELS...A SURFACE LOW ASSOCIATED WITH THE CLOSED
MIDLEVEL SYSTEM WILL OCCLUDE WHILE SLOWLY DEVELOPING NWD THROUGH
SWRN SASKATCHEWAN. BY AFTERNOON...AN ATTENDANT LEE TROUGH WILL
EXTEND SEWD THROUGH ERN MT AND THEN SWD THROUGH THE WRN DAKOTAS AND
WRN NEB TO A DEEPENING LEE CYCLONE ALONG THE KS/CO BORDER.
...DAKOTAS INTO WRN NEB...
THE SLOW EWD DEVELOPMENT OF A SURFACE HIGH ACROSS THE NRN GULF OF
MEXICO WILL EFFECTIVELY LIMIT THE POLEWARD RETURN OF MORE ROBUST
BOUNDARY LAYER MOISTURE DESPITE THE STRENGTHENING...SLY LOW-LEVEL
FLOW. AS SUCH...DAYTIME HEATING COUPLED WITH THE EWD PROGRESSION OF
HEIGHT FALLS/DYNAMIC COOLING IN THE EXIT REGION OF MID/UPPER-LEVEL
JETS WILL BE THE PRIMARY CONTRIBUTORS TO AIR MASS DESTABILIZATION
VIA STEEPENING OF AMBIENT LAPSE RATES. THESE PROCESSES ARE EXPECTED
TO SUPPORT AT LEAST WEAK CONVECTIVE INSTABILITY BY AFTERNOON INVOF
THE LEE TROUGH WHERE SBCAPE WILL APPROACH 500-700 J/KG.
THE ABOVE-MENTIONED FORCING/HEIGHT FALLS IN CONJUNCTION WITH
HEATING/DEEP BOUNDARY LAYER MIXING ARE EXPECTED TO FOSTER ISOLATED
TO WIDELY SCATTERED TSTMS ALONG THE LEE TROUGH BY LATE AFTERNOON OR
EARLY EVENING. FORECAST SOUNDINGS INDICATE THE DEVELOPMENT OF A
RATHER DEEP BOUNDARY LAYER WITH TEMPERATURE-DEW POINT SPREADS OF AOA
30-35 F. THIS DRY SUB-CLOUD LAYER IN CONCERT WITH A DEEP WLY WIND
FIELD AND RESULTANT 40+ KT OF 0-6 KM BULK SHEAR SUGGEST THE
POTENTIAL FOR LOCALLY DAMAGING DOWNBURST WINDS WITH ANY MORE
ORGANIZED STORM CLUSTERS. SOME HAIL MAY ALSO ACCOMPANY THE STRONGER
UPDRAFTS.
DIURNAL STORMS AND THE ISOLATED SEVERE WEATHER THREAT ARE EXPECTED
TO DIMINISH BY LATE EVENING AS THE BOUNDARY LAYER COOLS AND
STABILIZES.
..MEAD/GARNER.. 04/28/2010
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