SWODY1
SPC AC 180539
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT WED APR 18 2007
VALID 181200Z - 191200Z
..NO SVR TSTM AREAS FORECAST...
..SYNOPSIS...
LARGE OMEGA BLOCKING PATTERN WILL CONTINUE ACROSS THE MID AND HIGH
LATITUDES OF N. AMERICA WITH AN UNDERCUTTING STREAM OF STRONGER
ZONAL FLOW FROM THE ERN PACIFIC ACROSS THE SRN STATES. WITHIN THIS
LARGER-SCALE REGIME...MID-LEVEL TROUGH CURRENTLY DIGGING OVER THE
PACIFIC NW INTO GREAT BASIN WILL SHIFT MORE EWD PRIOR TO EJECTING IN
NEGATIVE TILT FASHION INTO THE NRN AND CNTRL HIGH PLAINS.
IN THE LOW-LEVELS...A RELATIVELY STRONG PACIFIC COLD FRONT ATTENDANT
TO THIS UPPER SYSTEM WILL PUSH EWD THROUGH THE ROCKIES INTO ADJACENT
HIGH PLAINS. ASSOCIATED SURFACE LOW IS FORECAST TO DEEPEN AS IT
DEVELOPS FROM NWRN WY INTO SERN MT BY THURSDAY MORNING.
..NRN/CNTRL ROCKIES INTO HIGH PLAINS...
LOW-LEVEL AIR MASS IS EXPECTED TO REMAIN RELATIVELY DRY AHEAD OF
PACIFIC COLD FRONT WITH DEWPOINTS COMMONLY IN THE 20S AND 30S.
HOWEVER...DAYTIME HEATING COUPLED WITH DYNAMIC COOLING ASSOCIATED
WITH CONCENTRATED HEIGHT FALL CENTER AHEAD OF UPPER SYSTEM WILL
RESULT IN THE DEVELOPMENT OF STEEP LOW TO MID-LEVEL LAPSE RATES
WITHIN PRE-FRONTAL AIR MASS. EXPECT SBCAPES TO RANGE FROM 200-400
J/KG OVER PORTIONS OF NERN UT/CO...TO 500-900 J/KG OVER S-CNTRL INTO
SERN MT.
TSTMS WILL LIKELY INITIALLY DEVELOP BY EARLY TO MID AFTERNOON ALONG
FRONT OR IN IMMEDIATE POST-FRONTAL AIR MASS FROM S-CNTRL MT SWD INTO
WRN WY AND NERN UT. SUBSEQUENT STORM DEVELOPMENT WILL THEN OCCUR
OVER PORTIONS OF CNTRL/ERN PARTS OF MT/WY SWD INTO WRN/CNTRL CO
THROUGH THE REMAINDER OF THE AFTERNOON INTO TONIGHT. THE STEEP
LAPSE RATES COUPLED WITH INCREASING VERTICAL SHEAR INDICATE THE
POTENTIAL FOR A FEW ORGANIZED STORMS CAPABLE OF SEVERE HAIL AND
LOCALLY DAMAGING WINDS.
FORECAST SOUNDINGS AND PLAN VIEW PROGNOSTIC FIELDS INDICATE THAT THE
STRONGEST VERTICAL SHEAR WILL REMAIN UPSTREAM OF THE STRONGER
INSTABILITY IN PLACE OVER MT...LEAVING SOME UNCERTAINTY AS TO WHERE
THE GREATEST SEVERE WEATHER THREAT WILL LIKELY EXIST.
THEREFORE...LOW WIND/HAIL PROBABILITIES HAVE BEEN ASSIGNED TO A
BROADER GEOGRAPHICAL AREA TO ADDRESS THIS UNCERTAINTY.
..WRN/CNTRL KY...
MID-LEVEL COLD POOL ATTENDANT TO UPPER LOW OVER THE OH VALLEY IS
EXPECTED TO CONTRIBUTE TO STEEPENING LAPSE RATES AND WEAK CONVECTIVE
INSTABILITY /SBCAPES OF 400-600 J PER KG/ INVOF WEAK SURFACE LOW AND
FRONT THIS AFTERNOON. ISOLATED/SCATTERED TSTMS WILL BECOME
INCREASINGLY LIKELY BY AFTERNOON ACROSS THE AREA...A FEW OF WHICH
COULD PRODUCE SOME SMALL HAIL. ANY SEVERE WEATHER THREAT APPEARS
TOO LOW TO WARRANT INCLUSION OF PROBABILITIES.
.MEAD/GRAMS.. 04/18/2007
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