SPC AC 020555
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1255 AM CDT FRI OCT 02 2009
VALID 021200Z - 031200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
AMPLIFIED YET PROGRESSIVE UPPER AIR PATTERN FCST TO CONTINUE ACROSS
CONUS THROUGH PERIOD. MID-UPPER LOW -- NOW OVER ST LAWRENCE VALLEY
AREA OF SRN QUE -- IS EXPECTED TO LIFT NEWD WHILE STG/TRAILING
SHORTWAVE TROUGH STRENGTHENS CONSIDERABLY...EFFECTIVELY SHIFTING
UPPER TROUGHING EWD ACROSS NEW ENGLAND EARLY IN PERIOD. AS THIS
OCCURS...BROAD UPPER CYCLONE NOW CENTERED OVER NWRN IA SHOULD MOVE
EWD ACROSS SRN WI TO VICINITY CENTRAL/SRN LM BY 3/12Z.
MEANWHILE...SPEED MAX ALOFT FROM ERN GULF OF AK TO SRN BC -- AND
ACCOMPANYING CHAIN OF MIDLEVEL VORTICITY LOBES -- IS FCST TO AMPLIFY
INTO CLOSED/BROAD CYCLONE OVER WA BY END OF PERIOD.
AT SFC...COLD FRONT IS ANALYZED FROM SERN MO SWWD ACROSS AR AND E TX
TO S-CENTRAL/SW TX. FRONT IS FCST TO CONTINUE SEWD ACROSS MID-SOUTH
AND W GULF COAST REGIONS...REACHING FROM CENTRAL/SRN APPALACHIANS
SWWD TO S-CENTRAL/SERN LA AND S-CENTRAL TX BY 3/00Z. S TX SEGMENT
OF THIS FRONT SHOULD STALL EARLY IN PERIOD...AND MAY START TO
RETREAT NWD AROUND 3/12Z. MEANWHILE...REMAINDER OF LA-GA FRONTAL
SEGMENT SHOULD DECELERATE...WITH NRN PORTION OF COLD FRONT MOVING
SLOWLY EWD FROM CENTRAL APPALACHIANS ACROSS PIEDMONT AND INLAND
MID-ATLANTIC. MARINE/WARN FRONTAL ZONE EXTENDS FROM SERN GULF NWWD
OVER SERN LA...THEN ROUGHLY NWD TO WHERE ONGOING CONVECTIVE BAND
CROSSES MS RIVER. THIS CONVECTION...AND COLD FRONT IMMEDIATELY
FOLLOWING IT...WILL OVERTAKE MARINE FRONT FROM N-S WHILE MARINE
FRONT MOVES SLOWLY EWD ACROSS LOWER DELTA REGION AND SRN PORTIONS
MS/AL.
...S TX...
TWO PERIODS OF MRGL/CONDITIONAL SVR POTENTIAL ARE APPARENT ACROSS
THIS REGION...OVERLAPPING SPATIALLY. AIR MASS INVOF SFC FRONTAL
ZONE...AND SWD TO LOWER RIO GRANDE VALLEY -- IS FCST TO DESTABILIZE
DURING AFTERNOON LARGELY BECAUSE OF SFC DIABATIC HEATING...GIVEN
LACK OF APPRECIABLE LARGE-SCALE/UPPER LEVEL SUPPORT. UPSTREAM CLOUD
TRENDS ATTM INDICATE CIRRUS-LEVEL EFFLUENT FROM PACIFIC TS OLAF
SHOULD BE RATHER THIN AND PATCHY...AND NOT A SIGNIFICANT IMPEDIMENT
TO SFC HEATING. WITH DEW POINTS GENERALLY UPPER 60S AND 70S
F...WEAKLY CAPPED MLCAPE TO NEAR 3000 J/KG IS POSSIBLE BY MID-LATE
AFTERNOON...ACCORDING TO MODIFIED WRF AND ETA-KF SOUNDINGS. NEGATIVE
FACTORS WILL INCLUDE WEAK LOW-MIDLEVEL WINDS...I.E. 10 KT OR LESS
THROUGH MOST OF SFC-700 MB LAYER. HOWEVER...STG UPPER WINDS --
AROUND 50-75 KT AT 250 MB NEAR SRN RIM OF UPPER JET MAX -- MAY
CONTRIBUTE TO ORGANIZATION OF ANY TSTMS THAT CAN DEVELOP. ANOTHER
LIMITING EFFECT WILL BE WEAKNESS OF LOW LEVEL CONVERGENCE...WITH STG
ELY FLOW COMPONENT ALONG BOTH SIDES OF SFC FRONTAL ZONE. A FEW
GUSTS/HAIL EVENTS NEAR SVR LEVELS ARE POSSIBLE.
LOW LEVEL MOIST/WARM ADVECTION MAY SUPPORT INCREASE IN ELEVATED
BUOYANCY AND POTENTIAL FOR STG/ISOLATED SVR TSTMS LATE IN PERIOD
OVER PORTIONS S-CENTRAL TX -- EITHER FROM ACTIVITY DEVELOPING OVER
THIS REGION OR MOVING NEWD FROM COAHUILA. MODIFIED FCST SOUNDINGS
SUGGEST POTENTIAL FOR 35-45 KT EFFECTIVE SHEAR MAGNITUDES AMIDST
ELEVATED MUCAPES 500-1500 J/KG. MAIN CONCERN WOULD BE MRGL
HAIL...ESPECIALLY AFTER APPROXIMATELY 06/03Z.
...COASTAL DELTA REGION TO WRN FL PANHANDLE...
ISOLATED STG/DAMAGING GUSTS CANNOT BE RULED OUT FROM CLUSTERS OR
SHORT LINEAR SEGMENTS OF TSTMS DEVELOPING IN NARROW WEDGE OF
HIGH-THETAE WARM SECTOR AIR NEAR COAST. COVERAGE IS IN QUESTION
GIVEN WEAKNESS OF LOW LEVEL WINDS AND OF NEAR-FRONTAL CONVERGENCE AS
A RESULT. HOWEVER...MLCINH ALSO SHOULD BE RATHER
LIMITED...ESPECIALLY DURING PERIOD OF DIABATICALLY-DRIVEN SFC
WARMING MID-DAY THROUGH MID-AFTERNOON. THIS AREA ALSO WILL RESIDE
BENEATH SOMEWHAT FAVORABLE UPPER LEVEL WINDS...AS ERN LOBE OF 250 MB
JET MAX PROPAGATES NWD ACROSS THIS AREA...WITH 60-80 KT FLOW
POSSIBLE AROUND ANVIL LEVEL. LACK OF MORE ROBUST LOW-MIDLEVEL SHEAR
WILL LIMIT ORGANIZED SVR THREAT.
..EDWARDS/GARNER.. 10/02/2009
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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