SPC AC 100557
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1157 PM CST WED JAN 09 2008
VALID 101200Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS TN VALLEY REGION TO
CENTRAL GULF COAST...
...SYNOPSIS...
IN MID/UPPER LEVELS...BROAD BELT OF GENERALLY CYCLONIC FLOW IS FCST
ACROSS MUCH OF CONUS THROUGH PERIOD. EMBEDDED/STRONG SHORTWAVE
TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY AND VWP/PROFILER
DATA OVER CENTRAL/SRN HIGH PLAINS -- IS FCST TO MOVE EWD ACROSS MS
VALLEY BY ABOUT 11/06Z. NORTHERN PORTION OF THIS PERTURBATION IS
FCST TO PHASE WITH SECOND/WEAKER TROUGH NOW DIGGING SEWD ACROSS SRN
SASK...RESULTING IN CLOSED OR NEARLY CLOSED 500 MB LOW OVER LOWER MI
BY END OF PERIOD. ABOUT HALF OF SREF MEMBERS AND LATEST OPERATIONAL
NAM...SPECTRAL AND ECMWF INDICATE THIS SCENARIO.
AT SFC...LOW INITIALLY OVER SWRN/S-CENTRAL KS SHOULD DEEPEN AS IT
LIFTS NEWD FROM SERN KS TOWARD LOWER MI DURING PERIOD. BY
11/12Z...SFC CYCLONE SHOULD BE OCCLUDED AND LOCATED CLOSE TO
MID/UPPER LEVEL VORTEX CENTER. SFC COLD FRONT -- NOW DEVELOPING SSW
OF LOW -- IS FCST TO STRENGTHEN ALSO...AND SWEEP SEWD ACROSS TX OVER
NWRN GULF...EWD ACROSS LOWER-MID MS VALLEY...REACHING CENTRAL/SRN
APPALACHIANS AND FL PANHANDLE BY 11/12Z. SFC MARINE/WARM FRONT --
NOW ANALYZED OVER EXTREME N-CENTRAL AND NWRN GULF...WILL BECOME
DIFFUSE AND MOVE INLAND ACROSS PORTIONS LA...SRN MS/AL AND FL
PANHANDLE. FURTHER NWD PENETRATION OF MARITIME/TROPICAL AIR MASS
INLAND IS UNCERTAIN ATTM.
...WRN/CENTRAL GULF COAST TO OH VALLEY/CENTRAL APPALACHIANS...
TSTMS ARE EXPECTED TO DEVELOP EARLY IN PERIOD...THEN THROUGHOUT
AFTERNOON AND EVENING HOURS...ALONG AND AHEAD OF SFC COLD FRONT.
MAIN CONCERNS APPEAR TO BE DAMAGING WIND INVOF FRONTAL CONVECTIVE
BAND...WITH POTENTIAL FOR TORNADIC SUPERCELLS AHEAD OF FRONT. IN
ADDITION TO DAMAGING NONTORNADIC GUSTS...TORNADIC MESOVORTICES IN
LEWP/BOW FORMATIONS ALSO ARE POSSIBLE.
MOST FAVORABLE JUXTAPOSITION OF RETURN FLOW MOISTURE...POTENTIAL SFC
HEATING AND STRONG LOW-MIDLEVEL KINEMATIC FIELDS APPEARS TO BE OVER
PORTIONS CENTRAL/ERN MS AND AL FROM MID-AFTERNOON INTO EVENING.
FORECAST IS SUBJECT TO UPGRADE IN SUBSEQUENT OUTLOOKS ONCE STORM
FOCI AND AREAS OF MOST FAVORABLE DIURNAL SFC HEATING BECOME BETTER
DEFINED.
VERTICAL SHEAR WILL BE VERY FAVORABLE ACROSS REGION WITH 50-60 KT OF
0-6 KM SHEAR COMMON BETWEEN TN VALLEY AND GULF COAST...AND BROADLY
CURVING LOW LEVEL HODOGRAPHS WITH 0-1 KM SRH VALUES OVER 200 J/KG
BEING COMMON.
AS IS TYPICAL WITH WINTER SVR EVENTS IN SERN CONUS...MAIN CAVEATS
FOR SVR THREAT INVOLVE THERMODYNAMIC SUPPORT. CLOUDS AND AREAS OF
PRECIP MAY LIMIT RATE OF DIURNAL HEATING ACROSS MUCH OF OUTLOOK
AREA...ESPECIALLY WITH DISTANCE FROM GULF COAST. PRIND SFC HEATING
AND DEW POINTS IN 60S F SHOULD BE SUFFICIENT TO OFFSET WEAK LAPSE
RATES ALOFT...TO YIELD MLCAPES 500-1000 J/KG NEAR GULF COAST. AREA
OF FAVORABLE BUOYANCY SHOULD NARROW AND WEAKEN IN MAGNITUDE NWD
AHEAD OF COLD FRONT...SUCH THAT MLCAPES AROUND 500 J/KG ARE ATTAINED
ONLY BRIEFLY FROM TN VALLEY REGION NWD INTO KY...WITH SFC-BASED
INSTABILITY NONEXISTENT TO VERY MRGL OVER OH BEFORE FROPA.
STRONGEST INFLUENCE ON RELATIVE POTENTIAL FOR DAMAGING WIND AND
TORNADOES WILL BE CONVECTIVE MODE. EXPECT LINEAR ORGANIZATION TO
EVOLVE WITH TIME INVOF INLAND PORTION OF SFC COLD FRONT...AS
LOW-MIDLEVEL SHEAR VECTORS BECOME ALIGNED MORE PARALLEL TO
BAROCLINIC ZONE. HOWEVER...SEGMENT OF FRONT NEAR COAST WILL REMAIN
MORE NORMAL TO AMBIENT FLOW ALOFT INTO OVERNIGHT HOURS...AND
DISCRETE DEVELOPMENT ALSO CANNOT BE RULED OUT IN
WEAKLY-CAPPED/PREFRONTAL WARM SECTOR. GIVEN THIS
SCENARIO...PRESENCE OF MULTIPLE CONVECTIVE MODES --
LINEAR...BOW/LEWP AND DISCRETE -- PRESENT IN HIGH
RESOLUTION/EXPERIMENTAL WRF RUNS APPEAR REASONABLE.
...ERN NC...
SVR POTENTIAL HERE APPEARS MRGL AND CONDITIONAL...LATE IN PERIOD.
AIR MASS MODIFICATION WILL CONTINUE ACROSS GULF STREAM...GRADUALLY
GIVEN ANTICYCLONIC TRAJECTORIES PROGGED OVER THIS REGION...WITH LOW
60S F SFC DEW POINTS INLAND AND MID 60S POSSIBLE ALONG COAST BY END
OF PERIOD. MODIFIED NAM-KF SOUNDINGS SUGGEST EFFECTIVE LIFTED
PARCELS MAY BECOME ROOTED AT OR VERY NEAR SFC BEFORE 11/12Z AS
BOUNDARY LAYER THETAE INCREASES...IN ENVIRONMENT OF 35-45 KT
DEEP-LAYER SHEAR. WEAK LAPSE RATES ALOFT WILL LIMIT BUOYANCY...AND
IMPORTANT FACTORS FOR FORCING CONVECTION...I.E. MESOSCALE BOUNDARY
DETAILS...REMAIN NEBULOUS.
..EDWARDS.. 01/10/2008
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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