Saturday, January 16, 2010

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 160558
SWODY1
SPC AC 160556

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1156 PM CST FRI JAN 15 2010

VALID 161200Z - 171200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
SPLIT FLOW PATTERN WILL CONTINUE ACROSS CONUS...S OF NRN-STREAM FLOW
BELT ACROSS CANADIAN BORDER. BROADLY CYCLONIC SRN STREAM FLOW IS
FCST AROUND PROGRESSIVE TROUGH PREDICTED TO MOVE FROM SRN PLAINS EWD
ACROSS LOWER MS VALLEY. MESO-ALPHA TO SYNOPTIC-SCALE TROUGH IS
CHARACTERIZED BY COMPLEX INTERACTION OF THREE SMALLER-SCALE BUT
WELL-DEFINED PERTURBATIONS. ATTM...TWO DISTINCT/CLOSED CIRCULATIONS
ARE ANALYZED ALOFT -- ONE CENTERED OVER MIDDLE TX COASTAL
PLAINS...ANOTHER DIGGING SSEWD FROM SWRN KS. THIRD SIGNIFICANT
PERTURBATION WITH THIS SYSTEM HAS BEEN CLOSED BEFORE...AND IS
EVIDENT IN MOISTURE CHANNEL IMAGERY ATTM OVER CENTRAL AND N-CENTRAL
MEX. KS LOW IS FCST TO PIVOT SEWD TOWARD N-CENTRAL TX THROUGH
17/00Z...THEN EWD ACROSS NRN LA DURING LATTER HALF OF
PERIOD...EFFECTIVELY ABSORBING LOW NOW OVER S TX. MEANWHILE...MEX
SHORTWAVE TROUGH IS FCST TO TURN NEWD...ACCELERATE AND
DEAMPLIFY...EJECTING ACROSS NWRN/N-CENTRAL GULF. OPERATIONAL
WRF/SPECTRAL...EARLIER ECMWF RUN AND MOST SREF MEMBERS REASONABLY
PROG THIS FEATURE TO MOVE NEWD OVER SERN LA AROUND 17/00Z...THEN
OVER SRN APPALACHIANS BY 17/12Z.

AT SFC...CYCLONE NOW ANALYZED OFFSHORE LOWER-MIDDLE TX COAST IS
EXPECTED TO LIFT NEWD OVER SWRN/S-CENTRAL LA EARLY IN PERIOD...BUT
WEAKENING AS OCCLUSION TRIPLE-POINT LOW DEVELOPS FARTHER E OVER
N-CENTRAL GULF. LATTER LOW...IN TURN...IS EXPECTED TO LIFT QUICKLY
NEWD ACROSS WRN PORTIONS FL PANHANDLE BETWEEN 16/18Z AND
16/00Z...LEAVING MARINE/WARM FRONTAL ZONE BEHIND OVER GULF WATERS.
SECONDARY WARM FRONTAL SEGMENT IS EXPECTED TO LIFT NWD ACROSS ERN GA
AND SC LATE IN PERIOD...DURING OVERNIGHT HOURS.

...FL PANHANDLE TO COASTAL BEND...SERN AL...SWRN GA...
SUFFICIENT DEEP-LAYER SHEAR TO SUPPORT SVR...AND ENLARGED LOW-LEVEL
HODOGRAPHS...EACH ARE PROBABLE ALONG AND S OF MARINE FRONT AND SE OF
ERN SFC LOW. THEREFORE...KEY FACTOR FOR SVR POTENTIAL WILL BE
PRESENCE OF SUFFICIENT BOUNDARY LAYER DESTABILIZATION. EFFECTIVE
INFLOW LAYER WILL BE ROOTED AT OR VERY NEAR SFC ALONG AND S OF WARM
FRONT...AND ALONG AND E OF COLD FRONT TRAILING GENERALLY SWD/SSWWD
FROM ERN SFC LOW. HOWEVER...EFFECTIVE WARM FRONTAL ZONE MAY NOT
REACH LAND OVER THIS REGION GIVEN COMBINATION OF
1. STG ISALLOBARIC FORCING E AND NE OF LOW...MAINTAINING ELY
COMPONENT WITH RELATIVELY STABLE AND MORE INCOMPLETELY MODIFIED
CONTINENTAL TRAJECTORIES AT SFC...AND
2. EXTENSIVE TSTMS AND PRECIP LIKELY ACROSS NRN GULF...ON BOTH SIDES
OF WARM FRONT.

OBSERVED POCKET OF STABLE AIR OVER NERN GULF -- RELATED TO
RELATIVELY COLD/SHALLOW SHELF WATERS -- IS WELL-RECOGNIZED BY MOST
OPERATIONAL PROGS...AND EVERY SREF PARTICIPANT BUT THE 5 RSM
MEMBERS. SHALLOW LAYER OF THIS AIR MASS WILL ADVECT INLAND OVER ERN
PANHANDLE AND SWRN GA...AND SHOULD LIMIT SVR POTENTIAL WITH SQUALL
LINE EXPECTED TO DEVELOP OVER NERN GULF.

GIVEN THESE UNCERTAINTIES AND MITIGATING FACTORS...SVR POTENTIAL
OVER LAND REMAINS VERY CONDITIONAL. THEREFORE...LOW-END
UNCONDITIONAL SVR PROBABILITIES WILL BE MAINTAINED FOR
NOW...EMPHASIZING MRGL WIND AND TORNADO THREATS.

...PENINSULAR FL TO COASTAL CAROLINAS...
FOR SOMEWHAT DIFFERENT REASONS...SHALLOW LAYER OF RELATIVELY
COOL/STABLE AIR ALSO COULD PRECLUDE ORGANIZED SVR EVENT OVER THIS
REGION...HOWEVER STRENGTH OF DEEP-LAYER SHEAR AND LIKELIHOOD OF
ORGANIZED SQUALL LINE DOES COMPEL AT LEAST MRGL SVR WIND AND TORNADO
PROBABILITIES ATTM. SOME PORTIONS OF THIS AREA MAY NEED TO BE
UPGRADED TO CATEGORICAL-THRESHOLD SVR PROBABILITIES IF
DESTABILIZATION TRENDS BEGIN TO APPEAR ONLY SLIGHTLY MORE FAVORABLE
THAN NOW PROGGED.

UNCERTAINTIES REGARDING BOUNDARY LAYER DESTABILIZATION AHEAD OF
SQUALL LINE ACROSS PENINSULAR FL NNEWD TO COASTAL CAROLINAS ARE
RELATED MAINLY TO COMBINATION OF
1. ANTECEDENT LOW THETAE AND LONG UPSTREAM FETCH OF ONLY PARTLY
MODIFIED AIR MASS...PRECLUDING FULL MARITIME/TROPICAL RECOVERY
ACROSS THIS REGION PRIOR TO SQUALL LINE PASSAGE...AND
2. PATH OF SFC CYCLONE AND RELATED ISALLOBARIC PATTERN RESULTING IN
SUSTAINED/SLY COMPONENT OF SFC FLOW ACROSS DIABATICALLY COOLED
NOCTURNAL LANDMASS AND/OR INCOMPLETELY MODIFIED MARINE AIR.

..EDWARDS.. 01/16/2010

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