SWODY2
SPC AC 200606
DAY 2 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
1206 AM CST THU DEC 20 2007
VALID 211200Z - 221200Z
..NO SVR TSTM AREAS FORECAST...
CORRECTED FOR MISSING GEN TSTM LINES
..SYNOPSIS...
PROGRESSIVE UPPER AIR PATTERN FCST TO CONTINUE OVER CONUS THROUGH
THIS PERIOD. SHORTWAVE TROUGH NOW OVER SRN PLAINS IS EXPECTED TO
MOVE ESEWD ACROSS SERN CONUS...MOVING OFFSHORE SC/GA/ERN FL DURING
BEFORE 21/18Z. ASSOCIATED SFC LOW WILL BE CLOSE TO COAST ALONG
FRONTAL ZONE THAT WILL DEMARCATE NELY FLOW AND COLD/DAMMING REGIME
TO N FROM MOIST BOUNDARY LAYER OF GULF ORIGIN TO S. PRIND BUOYANCY
WILL BE TOO LIMITED TO SUPPORT ORGANIZED SVR POTENTIAL OVER LAND
WITH THIS DEPARTING SYSTEM...BUT MAY SUPPORT GEN TSTM POTENTIAL FOR
FIRST FEW HOURS.
MOST RELEVANT PERTURBATIONS ARE INDICATED OVER MOISTURE CHANNEL
IMAGERY ATTM OFFSHORE NRN CA/ORE...AND OVER AK PANHANDLE/NWRN BC
REGION. AS PHASING/INTENSIFICATION OF EACH OF THESE SHORTWAVES
OCCURS...HIGH-AMPLITUDE/SYNOPTIC-SCALE TROUGH IS FCST TO DEVELOP
ACROSS WRN THEN CENTRAL CONUS EARLY THIS PERIOD. BY 22/12Z...NRN
SHORTWAVE SHOULD EVOLVE INTO CLOSED LOW OVER ND OR ADJACENT PORTIONS
SASK/MB. MEANWHILE SRN TROUGH ALSO MAY EVOLVE INTO 500 MB LOW
ACROSS NM AND W TX DURING 22/00Z-22/12Z TIME FRAME...WITH 80-90 KT
500 MB FLOW TO ITS S ACROSS SRN NM AND W TX...AND 100-120 KT 250 MB
JET MAX. AT SFC...COLD FRONT IS FCST TO INTENSIFY AS IT MOVES OUT
OF ROCKIES...BEFORE SWEEPING EWD ACROSS NRN PLAINS/UPPER MS
VALLEY...AND SEWD OVER MOST OF TX/OK.
SFC LOW SHOULD FORM OVER SRN HIGH PLAINS ALONG FRONT...AND IN
ADVANCE OF SRN MIDLEVEL TROUGH...HOWEVER CONSIDERABLE VARIATION
EXISTS AMONG SREF AND OPERATIONAL GUIDANCE PACKAGES ON ITS STRENGTH
AND SPEED OF ITS NEWD EJECTION ALONG FRONT. PREFRONTAL DRYLINE AND
WIND SHIFT LINE SHOULD EXTEND SWD ACROSS CENTRAL OR ERN TX BY END OF
PERIOD...MARKING WRN BOUND OF CONVECTIVE THREAT ACROSS TX.
..SE TX...ARKLATEX TO SRN OZARKS...
VERY CONDITIONAL SVR POTENTIAL EXISTS NEAR END OF DAY-2
PERIOD...22/09Z AND BEYOND...WHICH REPRESENTS SPATIAL OVERLAP OF TWO
REGIMES...
1. COLD FRONT BEGINNING TO IMPINGE ON NWRN PORTION OF INCREASINGLY
MOIST RETURN FLOW...BUT WITH HIGHLY VARIABLE PROGS OF ACTUAL
BOUNDARY LAYER MOISTURE CONTENT.
2. FREE WARM SECTOR AHEAD OF FRONT...PARTICULARLY NEAR UPPER TX
COAST AND ADJACENT PORTIONS SE TX...WHERE SFC THETAE MAY BECOME HIGH
ENOUGH TO SUPPORT SFC-BASED EFFECTIVE LIFTED PARCELS.
MAIN UNCERTAINTY FOR BOTH REGIMES INVOLVES MAGNITUDE OF MOISTURE AND
RESULTANT LOW LEVEL DESTABILIZATION WITHIN RETURNING GULF AIR MASS.
LONG-FETCH SLY TRAJECTORIES -- ROOTED IN WRN OPEN GULF AND BAY OF
CAMPECHE -- REASONABLY ARE APPARENT IN MANY PROGS BY END OF
PERIOD...E OF DRYLINE/WIND SHIFT. HOWEVER...OPERATIONAL
WRF/SPECTRAL AND MOST SREF MEMBERS DO NOT RETURN SFC DEW POINTS 60 F
OR HIGHER FARTHER INLAND THAN ROUGHLY CLL-LFK-POE. SEVERAL SREF
OUTLIERS MAY BE MORE REASONABLE IN THIS SCENARIO...GIVEN LACK OF
INTENSE/COLD FROPA DEEP INTO GULF WITH PRECEDING SYSTEM. VERTICAL
SHEAR WILL BE STRENGTHENING AND FAVORABLE FOR ORGANIZED SVR DURING
OVERNIGHT HOURS AS SRN WAVE APCHS. HOWEVER...GIVEN UNCERTAINTIES
OVER MOISTURE RETURN...AND OVER TIMING OF CONVECTIVE INITIATION NEAR
END OF PERIOD...WILL DEPICT ONLY MRGL PROBABILITIES ATTM.
.EDWARDS.. 12/20/2007
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