SWODY1
SPC AC 211959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT TUE OCT 21 2008
VALID 212000Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL/SRN HIGH
PLAINS...
...SYNOPSIS...
UPPER AIR PATTERN FCST TO AMPLIFY THROUGH REMAINDER PERIOD...LARGELY
ATTRIBUTABLE TO STG AND DEEPENING SHORTWAVE TROUGH INITIALLY
ANALYZED FROM CENTRAL MT SWD TO NRN PORTIONS CO/UT BORDER. STRONGLY
MERIDIONAL/130-150 KT JET MAX AT 250 MB IS FCST TO TRANSLATE EWD
BEHIND THIS TROUGH AND ALONG CANADIAN BORDER...WHILE AOA 100 KT
SPEED MAX BUILDS SWD ACROSS SRN ROCKIES TO SRN HIGH PLAINS AND
ASSUMES STG CYCLONIC CURVATURE. BY END OF PERIOD...TROUGH SHOULD BE
CROSSING HIGH PLAINS...AND EXTENDING FROM WRN DAKOTAS TO TX
PANHANDLE. CONSIDERABLE AGEOSTROPHIC FORCING ALOFT AND RELATED
ENHANCEMENT TO LARGE SCALE UVV ARE EXPECTED IN LEFT EXIT REGION OF
JET MAX...ACROSS S-CENTRAL PLAINS.
SURFACE COLD FRONT -- ANALYZED ATTM FROM WRN DAKOTAS SSWWD ACROSS
SERN WY -- IS FCST TO INTENSIFY AND PLUNGE SWD ACROSS HIGH PLAINS TO
SRN TX PANHANDLE AND E-CENTRAL/SERN NM BY 12Z. INITIALLY WEAK SFC
LOW -- CURRENTLY ANALYZED OVER SERN CO -- IS FCST TO BECOME MORE
WELL-DEFINED AND INTENSE...SHIFTING/REDEVELOPING NEWD ALONG FRONT TO
NERN KS BY END OF PERIOD. BROAD SFC WARM FRONTAL ZONE -- REINFORCED
ACROSS WRN KS BY DIFFERENTIAL DIABATIC HEATING ON EDGE OF LOW CLOUD
FIELD -- IS ANALYZED FROM SWRN MO WNWWD ACROSS EXTREME S-CENTRAL
KS...NWWD TO SWRN NEB. COLD FRONT WILL OVERTAKE THIS BOUNDARY FROM
NW-SE WITH TIME.
...SRN/CENTRAL PLAINS...
EXPECT STG LARGE SCALE ASCENT -- NOW SUPPORTING ENVIRONMENT FOR
TSTMS ACROSS HIGH TERRAIN OF NRN/WRN CO -- TO SHIFT ONTO HIGH PLAINS
DURING NEXT SEVERAL HOURS AND INTERACT WITH INCREASING LOW LEVEL
MOISTURE...BOTH AT AND ABOVE SFC. AS THIS OCCURS...ALONG WITH
STRENGTHENING LOW LEVEL FRONTOGENETIC FORCING...CONVECTION WILL
DEVELOP AND INCREASE RAPIDLY IN COVERAGE. ACTIVITY INITIALLY OVER
CENTRAL HIGH PLAINS SHOULD EXPAND/BACKBUILD SWWD INVOF COLD FRONT
WITH TIME...AS FRONT MOVES SEWD AND EWD ACROSS REGION. AS COLD
FRONT OVERTAKES WARM FRONT...AND STRONGEST LARGER SCALE LIFT
OVERSPREADS AREA FROM NW-SE...MOST FAVORABLY UNSTABLE ENVIRONMENT
WILL BE SHUNTED SEWD. RESULT OF THESE PROCESSES COULD BE NET
FAN-SHAPED GROWTH OF CONVECTIVE REGIME SIMILAR TO ORIENTATION OF
CATEGORICAL OUTLOOK...AND INCREASE IN SVR POTENTIAL THROUGH
AFTERNOON AND EARLY EVENING. SVR THREAT WILL PEAK THIS EVENING THEN
DIMINISH BY 09-12Z TIME FRAME AS FOREGOING NEAR-SFC AIR MASS BECOMES
MORE STABLE.
STG-SVR GUST POTENTIAL WILL BE RELATIVELY MAXIMIZED FOR SEVERAL
HOURS LATE THIS AFTERNOON AND EVENING...ESPECIALLY WITH TSTMS
ALONG/AHEAD OF COLD FRONT...UNTIL FOREGOING NEAR-SFC LAYER COOLS
SUFFICIENTLY TO RAISE BASE OF EFFECTIVE INFLOW LAYER ABOVE SFC.
LARGE HAIL WILL BE POSSIBLE FROM ACTIVITY BOTH NEAR AND BEHIND COLD
FRONT. PREDOMINANT CONVECTIVE MODE WILL BE LINEAR FOR MOST OF
PERIOD...ALTHOUGH EARLY/RELATIVELY DISCRETE CONVECTION MAY ATTAIN
SUPERCELLULAR MODE. ANY SUCH ACTIVITY THAT CAN INTERACT WITH
DIFFERENTIAL HEATING/WARM FRONTAL BOUNDARY...BEFORE INFLOW LAYER
BECOMES ELEVATED...MAY POSE TORNADO THREAT...GIVEN VERY LARGE SIZE
OF LOW LEVEL HODOGRAPHS EXPECTED IN THAT FRONTAL ZONE.
HOWEVER...TORNADO POTENTIAL APPEARS TOO CONDITIONAL/ISOLATED FOR
MORE THAN MRGL PROBABILITIES ATTM.
..EDWARDS.. 10/21/2008
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