SWODY2
SPC AC 011729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CST MON MAR 01 2010
VALID 021200Z - 031200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS E-CENTRAL AND SRN FL
AND KEYS...
...SYNOPSIS...
HIGH-AMPLITUDE BUT PROGRESSIVE SYNOPTIC-SCALE PATTERN IS FCST ACROSS
CONUS THROUGH PERIOD. COMPACT MID-UPPER LEVEL CYCLONE NOW ANALYZED
OVER CENTRAL TX IS FCST TO BECOME ENTRAINED WITHIN BROADER REGIME OF
CYCLONIC FLOW ACCOMPANYING MEAN ERN NORTH-AMERICAN TROUGHING. AS
THIS OCCURS...IT WILL LOSE SOME AMPLITUDE...BUT STILL PROGRESS EWD
FROM MS/AL COAST TO NRN FL BY 3/00Z...THEN EJECT NEWD ACROSS COASTAL
CAROLINAS THROUGH REMAINDER PERIOD.
AT SFC...LOW NOW DEVELOPING OFFSHORE GLS IS FCST TO DEEPEN AND MOVE
GENERALLY EWD ACROSS EXTREME NRN GULF SHELF WATERS UNTIL BEGINNING
OF PERIOD...THEN CROSS PORTIONS CENTRAL/ERN PANHANDLE OF
FL...EXTREME NRN FL AND SERN GA DURING 2/12Z-2/18Z TIME FRAME. LOW
THEN SHOULD MOVE/REDEVELOP EWD OVER ATLANTIC WATERS...OFFSHORE GA
COAST...BY 2/21Z. CONSIDERABLE DEEPENING IS FCST AS CYCLONE THEN
LIFTS NEWD OFFSHORE CAROLINAS THROUGH REMAINDER PERIOD. TRAILING
COLD FRONT WILL SWEEP EWD FROM ERN GULF ACROSS FL PENINSULA AND KEYS
BY 2/21Z...CATCHING UP WITH ANTECEDENT/PREFRONTAL SFC TROUGH AND
WIND-SHIFT LINE AS ATLANTIC LOW DEVELOPS/DEEPENS.
MEANWHILE...RIDGING ALOFT WILL SHIFT EWD FROM GREAT BASIN AND NRN
ROCKIES ACROSS SRN ROCKIES AND NRN PLAINS...AS NEXT SERIES OF STG
PERTURBATIONS APCH PAC COAST. PRIMARY MID-UPPER VORTICITY LOBE
ACCOMPANYING SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL
IMAGERY W OF CA AROUND 135W -- IS FCST TO MOVE ASHORE CENTRAL CA
AROUND 2/21Z. THIS FEATURE THEN WILL LIFT NEWD ACROSS SIERRAS AND
WEAKEN OVERNIGHT...AS STRONGER TROUGH AND EMBEDDED CYCLONE ALOFT DIG
SEWD TOWARD NRN CA.
...FL...
BAND OF CONVECTION WITH EMBEDDED TSTMS IS EXPECTED TO MOVE EWD FROM
GULF ACROSS PENINSULAR FL AND KEYS...WITH CONDITIONAL DAMAGING GUST
AND TORNADO POTENTIAL. PRIND ACTIVITY WILL MOVE ACROSS NRN/CENTRAL
FL DURING 2/12Z-2/15Z TIME FRAME...AND S FL/KEYS FROM
2/15Z-2/18Z...PROBABLY JUST AHEAD OF COLD FRONT AND INVOF PREFRONTAL
TROUGH WHERE LOW-LEVEL CONVERGENCE WILL BE RELATIVELY MAXIMIZED.
ATLANTIC LOW DEVELOPMENT FARTHER NE...AND RELATED READJUSTMENT OF
ISALLOBARIC FIELDS...ARE EXPECTED TO RESULT IN WARM-SECTOR FLOW
VEERING WITH TIME PRIOR TO FROPA...AND PERHAPS PRIOR TO PASSAGE OF
CONVERGENCE/CONVECTIVE BAND. NONETHELESS...FCST SOUNDINGS AND
HODOGRAPHS SUGGEST AMPLE LOW-LEVEL AND DEEP-LAYER SHEAR TO SUPPORT
SVR POTENTIAL. WINDS NEAR 500 MB WILL BE ABOUT 70-80 KT OVER
CENTRAL/S FL...SUPPORTING 0-6 KM AND EFFECTIVE SHEAR VALUES AROUND
50 KT EVEN FOR SSWLY SFC WINDS...AND OF COURSE HIGHER VALUES IF
INCLUDING ANY REMAINING SLY/SSELY WINDS INVOF E COAST.
MAIN CONCERN ATTM IS LACK OF MORE MATURE MARITIME-TROPICAL
MODIFICATION TO UPSTREAM TRAJECTORIES WITHIN BOUNDARY LAYER AIR MASS
OVER THIS REGION...AND RESULTANT RELATIVE WEAKNESS IN THETAE OVER
PENINSULA PRIOR TO FROPA. HOWEVER...NARROW CORRIDOR OF 60S F SFC
DEW POINTS MAY RETURN TO PORTIONS S FL AND ARE LIKELY OVER KEYS
PRIOR TO CONVECTION. IN ACCORDINGLY MODIFIED SOUNDINGS...THIS
OFFSETS WEAK LAPSE RATES ALOFT...JUST ENOUGH TO YIELD SFC-BASED
BUOYANCY AND MLCAPE UP TO ABOUT 700 J/KG. WHILE STILL NOT
HIGH-CONFIDENCE...SVR POTENTIAL APPEARS PROBABLE ENOUGH NOW THAT
CATEGORICAL OUTLOOK CAN BE INTRODUCED FOR PORTIONS E-CENTRAL/SRN FL
AND KEYS...PERHAPS EXPANDED UPSTATE IN LATER OUTLOOKS FOR THIS
PERIOD AS NECESSARY.
...CA...
CLIMATOLOGICALLY FAVORABLE TIMING OF ARRIVAL OF NEGATIVELY TILTED
SHORTWAVE TROUGH...WITH PRECEDING ENHANCEMENTS TO DEEP-LAYER
SHEAR...SUGGESTS CONDITIONAL POTENTIAL FOR SVR GIVEN SUSTAINED AND
SFC-BASED CONVECTION. AS OFTEN...MAIN CONCERN/UNCERTAINTY THIS FAR
OUT IN TIME IS WHETHER BOUNDARY LAYER CAN DESTABILIZE SUFFICIENTLY
TO SUPPORT SUCH ACTIVITY...ESPECIALLY OVER CENTRAL VALLEY WHERE
OROGRAPHICALLY FORCED BACKING OF NEAR-SFC WINDS WOULD MAXIMIZE
LOW-LEVEL SHEAR. ATTM...IT IS TOO SOON TO INTRODUCE ON CONDITIONAL
SVR PROBABILITIES AOA 5 PERCENT...HOWEVER THIS MAY BE NEEDED IN
SUCCEEDING OUTLOOKS.
..EDWARDS.. 03/01/2010
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