SWODY2
SPC AC 201730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT MON OCT 20 2008
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL/SRN PLAINS...
...SYNOPSIS...
UPPER AIR PATTERN FCST TO REMAIN PROGRESSIVE THROUGH
PERIOD...FEATURING INLAND AMPLIFICATION OF STG SHORTWAVE TROUGH NOW
MOVING ASHORE PACIFIC NW. AS THIS SYSTEM MOVES INLAND AND AMPLIFIES
DAY-2...STG HEIGHT FALLS ARE FCST ACROSS MOST OF CENTRAL/NRN
PLAINS...INCLUDING PORTIONS SRN PLAINS DURING LATTER 1/3 OF PERIOD.
ASSOCIATED SFC COLD FRONT IS FCST TO MOVE EWD AND SEWD OUT OF NRN
ROCKIES EARLY IN PERIOD...REACHING FROM VICINITY SK/MB BORDER SWD
ACROSS CENTRAL DAKOTAS...SSWWD TO E-CENTRAL CO...BY 22/00Z. AROUND
THAT TIME...SFC CYCLONE SHOULD DEVELOP ALONG CENTRAL HIGH PLAINS
PORTION OF FRONT...EJECTING EWD THEN NEWD ACROSS KS AS 500 MB LOW
DEVELOPS ACROSS WRN/SWRN NEB.
ELSEWHERE...MID-UPPER LEVEL TROUGH -- NOW EVIDENT IN MOISTURE
CHANNEL IMAGERY OVER UPPER MS VALLEY AND NRN ONT -- IS EXPECTED TO
CONTINUE AMPLIFYING...WITH CLOSED 500 MB LOW EVOLVING OVER ERN
ONT/LOWER GREAT LAKES REGION DURING 21/12Z-22/00Z TIME FRAME. THIS
LOW SHOULD CONTINUE ESEWD ACROSS CENTRAL/SRN NY AND COASTAL NEW
ENGLAND BY 22/12Z.
...CENTRAL/SRN PLAINS...
TWO ROUNDS OF CONVECTION ARE FCST THIS PERIOD. FIRST IS EXPECTED
BETWEEN NERN NM AND CENTRAL KS...ONGOING AT 21/12Z IN ZONE OF
ELEVATED LOW LEVEL WAA...AND FAVORABLY STEEP LAPSE RATES ABOVE WHAT
IS LEFT OF NOCTURNAL INVERSION CAPPING BOUNDARY LAYER. LACK OF MORE
SUBSTANTIAL THETAE -- WITHIN LAYER BEING RAISED TO LFC -- WILL LIMIT
MUCAPES TO AOB 200 J/KG MOST AREAS...AND KEEPS SVR POTENTIAL TOO
WEAK/DISORGANIZED FOR PROBABILITIES FOR THAT REGIME ATTM.
HOWEVER...MANY OF SAME AREAS...AS WELL AS FARTHER NW ACROSS ERN CO
AND EWD OVER MORE OF KS/OK...MAY EXPERIENCE POTENTIAL FOR STG-SVR
GUSTS AND HAIL LATER IN PERIOD INVOF COLD FRONT. STG FRONTOGENETIC
FORCING...AT LEAST MRGL LOW LEVEL MOISTURE...AND STRENGTHENING LARGE
SCALE ASCENT WILL SUPPORT INCREASINGLY FAVORABLE ENVIRONMENT FOR
TSTMS WITH TIME FROM LATE AFTERNOON OVER ERN CO THEN EWD AND SEWD
ACROSS MUCH OF KS AND WRN/NRN OK OVERNIGHT. TSTMS ALONG OR JUST
AHEAD OF SFC COLD FRONT WILL BEAR GREATEST POTENTIAL FOR DAMAGING
GUSTS...WHICH APPEARS BARELY SUFFICIENT IN COVERAGE SENSE TO UPGRADE
FOR CATEGORICAL OUTLOOK ATTM. ALTHOUGH BEST ORGANIZED CONVECTION
WILL MOVE INTO RELATIVELY COOL/STABLE NEAR-SFC AIR MASS ACROSS KS/OK
DURING 22/03Z-22/12Z TIME FRAME...FCST SOUNDINGS SUGGEST EFFECTIVE
INFLOW PARCELS STILL ROOTED AT OR NEAR SFC. ISOLATED LARGE HAIL
ALSO IS POSSIBLE FROM ACTIVITY ON BOTH SIDES OF FRONT.
ADDITIONAL/SEPARATE CLUSTER OF TSTMS MAY DEVELOP FROM EVENING
OVERNIGHT ACROSS PORTIONS LOWER MO VALLEY REGION INTO IA. THIS
REPRESENTS NEWD DISPLACEMENT OF SIMILAR REGIME TO THAT DESCRIBED
ABOVE FOR EARLY IN PERIOD...BUT WITH SOMEWHAT LARGER ELEVATED
MUCAPES -- 500-1000 J/KG -- REFLECTING ANOTHER 12-14 HOURS OF
MOISTURE RETURN AND ISENTROPIC ASCENT ABOVE SFC. SMALL HAIL IS
POSSIBLE...BUT WEAK MIDLEVEL WINDS RESTRICT EFFECTIVE SHEAR
MAGNITUDES TO BETWEEN 15-35 KT IN NAM-KF FCST SOUNDINGS.
..EDWARDS.. 10/20/2008
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