SWODY1
SPC AC 220102
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0802 PM CDT THU MAY 21 2009
VALID 220100Z - 221200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MID-UPPER LEVEL PATTERN REMAINS CHARACTERIZED BY
PROGRESSIVE/LOW-AMPLITUDE NRN STREAM INVOF CANADIAN BORDER...BROAD
CYCLONE OVER NERN GULF THAT ALSO EXTENDS TO SFC...AND BROAD/DIFFUSE
AREA OF TROUGHING OVER SWRN CONUS AND NRN MEX. LATTER WILL
CONTRIBUTE TO LINGERING GEN TSTM POTENTIAL FOR SEVERAL MORE
HOURS...ACROSS BROAD SWATH FROM PORTIONS CENTRAL/ERN GREAT BASIN TO
CENTRAL CO AND SWD TO MEX BORDERLANDS OF AZ/NM. EXPECT GRADUAL
DIMINISHMENT OF THUNDER COVERAGE AS COMBINATION OF CONVECTIVE
OUTFLOW AND DIABATIC COOLING STABILIZES AIR MASS THIS EVENING.
MEANWHILE...GULF LOW IS EXPECTED TO CONTINUE DRIFTING NWWD THROUGH
AN AREA ROUGHLY EQUIDISTANT BETWEEN EYW-MSY.
AT SFC...COLD FRONT IS ANALYZED FROM LM SWWD ACROSS SERN
IA...BECOMING QUASISTATIONARY OR DRIFTING SWD IN SEGMENTS FROM SWRN
IA ACROSS SERN NEB...NWRN TO EXTREME W-CENTRAL KS TO EXTREME SERN
CO. FRONT THEN INTERSECTS OUTFLOW BOUNDARY WITH WEAK SFC LOW OVER
SERN CO. OUTFLOW BOUNDARY EXTENDS SWWD ACROSS NERN NM BETWEEN
RTN-LVS.
...COASTAL FL...
DEEP-LAYER CYCLONE IS FCST TO REMAIN WELL OFFSHORE THROUGH REMAINDER
PERIOD...WHILE DRIFTING STEADILY FARTHER AWAY FROM PENINSULAR W
COAST. AS THIS OCCURS...RELATED ENHANCEMENTS TO LOW-MIDLEVEL WINDS
SHOULD RETREAT FARTHER OFFSHORE FROM W COAST...LEADING TO WEAKENING
OF BOTH LOW LEVEL HODOGRAPHS AND DEEP-LAYER SHEAR.
MEANWHILE...NRN/NERN FRINGES OF FAVORABLE WINDS ARE FCST TO REMAIN
OFFSHORE MOST OF ERN GULF COAST REGION...WITH POSSIBLE EXCEPTION OF
IMMEDIATE COASTAL AREAS ALONG PORTIONS FL PANHANDLE DURING LAST FEW
HOURS OF PERIOD. ALTHOUGH BULK OF SFC-BASED TSTMS SHOULD BE
OFFSHORE OVER GULF...ISOLATED TO WIDELY SCATTERED CONVECTION IS
POSSIBLE OVER LAND. BY 09Z-12Z TIME FRAME...SFC-BASED BUOYANCY WILL
BE VERY WEAK -- LESS THAN 300 J/KG OVER LAND -- INDICATING ANY
TORNADO POTENTIAL WILL BE VERY BRIEF AND CONDITIONAL...WITH
UNCONDITIONAL PROBABILITIES TOO SMALL FOR CATEGORICAL OUTLOOK.
...CENTRAL HIGH PLAINS...
QUASI-LINEAR MCS...LOCATED N OF FRONTAL AND OUTFLOW BOUNDARIES...IS
PROPAGATING GENERALLY NWD INTO ZONE OF LOWER SFC TEMPS BUT GREATER
LOW LEVEL MOISTURE CONTENT. INITIALLY MRGL SVR POTENTIAL IS
EXPECTED TO DIMINISH FURTHER DURING NEXT FEW HOURS...AND SVR
PROBABILITIES APPEAR TO HAVE DROPPED BELOW 5 PERCENT OVER THIS
REGION. COMBINATION OF ONGOING CONVECTIVE PROCESSES...SEASONALLY
WEAK LAPSE RATES ALOFT -- RELATED TO ADVECTIONS FROM CONVECTIVELY
OVERTURNED QUASI-MONSOONAL REGIME OVER SWRN CONUS -- AND DIABATIC
SFC COOLING WILL FURTHER REDUCE BUOYANCY THROUGH REMAINDER EVENING.
..EDWARDS.. 05/22/2009
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