SWODY1
SPC AC 200601
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0101 AM CDT WED MAY 20 2009
VALID 201200Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF WRN AND N
CENTRAL NEB AND VICINITY...
...SYNOPSIS...
MID-/UPPER-LEVEL TROUGH WILL CONTINUE PROGRESSING ACROSS THE NWRN
U.S. THROUGH THE FIRST HALF OF THE PERIOD...BUT SHOULD BE SHUNTED
ENEWD WITH TIME AS IT ENCOUNTERS A STOUT ERN U.S. RIDGE.
MEANWHILE...A WEAKER UPPER LOW WILL CONTINUE DRIFTING TOWARD THE
SWRN STATES. ELSEWHERE...A SECOND UPPER LOW IS FORECAST TO CONTINUE
DRIFTING SLOWLY WWD ACROSS THE ERN GULF GULF.
AT THE SURFACE...A LOW ASSOCIATED WITH THE ERN GULF SYSTEM ALOFT
WILL ALSO DRIFT WWD TOWARD THE CENTRAL GULF...WITH SHOWERS AND
THUNDERSTORMS LINGERING OVER FL THROUGH AT LEAST THE FIRST HALF OF
THE PERIOD.
FARTHER NW...A COLD FRONT IS FORECAST TO SHIFT SEWD ACROSS THE N
CENTRAL CONUS...AHEAD OF THE ADVANCING UPPER SYSTEM. BY
AFTERNOON...THE FRONT SHOULD EXTEND FROM MN SWWD INTO NEB...AND THEN
WILL CONTINUE EWD TO EXTEND FROM LAKE SUPERIOR/WI SWWD INTO WRN KS
BY 21/12Z. THIS FRONT SHOULD BE A FOCUS FOR AFTERNOON CONVECTIVE
DEVELOPMENT AND LIMITED/ASSOCIATED SEVERE POTENTIAL.
...CENTRAL/NRN PLAINS...
SLY ADVECTION OF LOW-LEVEL MOISTURE COMBINED WITH DAYTIME HEATING
WILL RESULT IN A ZONE OF APPRECIABLE DESTABILIZATION AHEAD OF THE
SEWD-MOVING COLD FRONT -- PARTICULARLY FROM ERN SD/SWRN MN SWWD
ACROSS SRN SD/NRN AND WRN NEB. CONVECTIVE DEVELOPMENT -- INITIALLY
FORECAST OVER ERN WY DURING THE AFTERNOON -- SHOULD SPREAD/DEVELOP
ENEWD INTO NRN NEB/SRN AND ERN SD AND POSSIBLY SWRN MN THROUGH THE
AFTERNOON/EVENING.
WITH LOW-LEVEL SLYS VEERING TO WSWLY AT 25 TO 35 KT AT MID
LEVELS...SHEAR BE SUFFICIENT FOR ORGANIZED STORMS/MID-LEVEL
ROTATION. WHILE RELATIVELY DEEP MIXED LAYER MAY SUPPORT
EVAPORATIVELY-DRIVEN/GUSTY SURFACE WINDS...THE PRIMARY SEVERE
POTENTIAL APPEARS TO BE HAIL. WHILE SEVERE POTENTIAL SHOULD SLOWLY
DIMINISH OVERNIGHT...SOME LIMITED THREAT MAY PERSIST THROUGH THE END
OF THE PERIOD...AS ELEVATED STORMS DEVELOP IN AN ANAFRONTAL MANNER.
...FL...
WHILE A SURFACE FLOW OFF THE SWRN FL COAST SHOULD PROGRESS WWD
ACROSS THE ERN GULF WITH TIME...THE ERN FRINGE OF THE UPPER
CIRCULATION SHOULD LINGER ACROSS FL THROUGH THE PERIOD. THIS WILL
SUPPORT ANOTHER DAY OF SCATTERED SHOWERS AND STORMS OVER THE FL
PENINSULA. WHILE INSTABILITY SHOULD REMAIN LIMITED...ENHANCED
LOW-LEVEL VEERING/SHEAR SUGGESTS A LIMITED THREAT FOR ISOLATED/BRIEF
TORNADOES...AND THUS WILL MAINTAIN LOW SEVERE PROBABILITIES THIS
FORECAST.
..GOSS/GRAMS.. 05/20/2009
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