SWODY3
SPC AC 250829
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0229 AM CST SUN DEC 25 2011
VALID 271200Z - 281200Z
...SYNOPSIS...
IN MID-UPPER LEVELS...BROAD BELT OF CYCLONIC FLOW FCST ACROSS CONUS
BY END OF PERIOD...AS NRN-STREAM HEIGHT FALLS LEAD TO INCREASING
CONJOINMENT OF NRN AND SRN STREAMS. MID-UPPER CYCLONE -- NOW
EVIDENT IN MOISTURE CHANNEL IMAGERY OVER SERN NM AND FAR W TX --
SHOULD BE DEAMPLIFYING AND MOVING ENEWD ACROSS ERN AR REGION BY
27/12Z. THIS SYSTEM SHOULD FURTHER DEVOLVE TO OPEN-WAVE TROUGH
THROUGH DAYLIGHT HOURS...MOVING UP OH VALLEY AND OVER SRN
APPALACHIANS AROUND 28/00Z...THEN ENEWD ACROSS MID-ATLANTIC REGION
AROUND END OF PERIOD.
AT SFC...INITIALLY PRIMARY SFC LOW SHOULD MOVE ENEWD FROM TN INTO
CENTRAL APPALACHIANS. SECONDARY/TRIPLE-POINT CYCLOGENESIS POSSIBLE
AROUND 28/00Z OVER NC/VA PIEDMONT...DEEPENING AND MOVING NEWD OVER
DELMARVA TOWARD SRN NEW ENGLAND COAST. AS THIS OCCURS...TRAILING
COLD FRONT WILL SWEEP EWD FROM TN VALLEY ACROSS SRN APPALACHIANS AND
OFFSHORE CAROLINAS. SRN SEGMENT OF FRONT SHOULD MOVE EWD ACROSS FL
PANHANDLE AND NERN GULF TO NEAR WRN COAST OF FL PENINSULA BY
28/00Z...THEN THROUGH REMAINDER PENINSULA BY 28/12Z. OPERATIONAL
NAM MAY BE TOO AGGRESSIVE WITH INLAND DESTABILIZATION OF RETURN FLOW
IN THIS REGIME...ESPECIALLY GIVEN LIKELIHOOD OF ANTECEDENT PRECIP
AND/OR SHORT/INCOMPLETE RETURN-FLOW TRAJECTORIES IN SERN CONUS. AS
SUCH...LATEST SPECTRAL/ECMWF ARE MORE HEAVILY WEIGHTED FOR THIS
FCST.
...ERN GULF COAST REGION...
SVR POTENTIAL OVER THIS AREA WILL BE DURING MORNING INTO EARLY
AFTERNOON...CARRYING OVER REGIME OF QUASI-LINEAR CONVECTIVE BAND
NEAR COLD FRONT AS DESCRIBED IN DAY-2 OUTLOOK. LOW-LEVEL AND
DEEP-LAYER SHEAR WILL BE FAVORABLE...WITH GREATEST POTENTIAL FOR
SFC-BASED EFFECTIVE LIFTED PARCELS BEING NEAR AND S OF I-10 AND W OF
I-75. WEAK LAPSE RATES AND UNCERTAINTIES REGARDING INLAND
PENETRATION OF HIGH-THETAE MARINE AIR PRECLUDE MORE THAN MRGL
UNCONDITIONAL SVR PROBABILITIES ATTM.
...SRN/ERN CAROLINAS...
AS WITH ERN GULF COAST REGIME...EXPECT STG SHEAR BY MANY
MEASURES...MAIN CAVEATS BEING CONVECTIVE MODE AND INSTABILITY.
SUBSTANTIAL SLY SFC FLOW COMPONENT SHOULD BE SUSTAINED FOR SEVERAL
HOURS AHEAD OF COLD FRONT AND/OR ANY PRE-FRONTAL TROUGH/CONVERGENCE
LINE THAT MAY DEVELOP. THIS WILL ADVECT AT LEAST PARTIALLY MODIFIED
MARINE AIR INLAND FROM ATLC...MAIN UNCERTAINTIES BEING
1. HOW FAR INLAND FOR NEAR-SFC BASED PARCELS AND
2. HOW MUCH MODIFICATION...I.E. WHETHER BOUNDARY-LAYER THETAE WILL
BE HIGH ENOUGH TO OFFSET POOR MIDLEVEL LAPSE RATES AND YIELD
SUPPORTIVE MLCAPE.
..EDWARDS.. 12/25/2011
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