SPC AC 040450
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1150 PM CDT SAT OCT 03 2009
VALID 041200Z - 051200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
UPPER AIR PATTERN ACROSS CONUS WILL CONTINUE TO BE DOMINATED BY
THREE PRIMARY FEATURES...
1. BROAD CYCLONE LIFTING NWD FROM UPPER GREAT LAKES OVER NRN ONT.
2. STRONGER VORTEX DIGGING SWD FROM NWRN GREAT BASIN...THEN PIVOTING
EWD OR ENEWD ACROSS NV...WHICH WILL INDUCE HEIGHT/PRESSURE FALLS
OVER CENTRAL ROCKIES REGION...AND BROAD ZONE OF LOW-LEVEL WAA OVER
CENTRAL/SRN PLAINS NW OF GULF COAST CONVECTIVE REGIME.
3. BROAD FETCH OF WSWLY SRN STREAM FLOW FROM NRN MEX ACROSS WRN GULF
COAST REGION...WITHIN WHICH HEIGHTS ARE FCST TO RISE THROUGH MOST OF
PERIOD. LIKEWISE...SRN RIM OF UPPER JET WILL SHIFT NWD ACROSS
SRN/CENTRAL TX...WITH FLOW BECOMING SLIGHTLY ANTICYCLONIC ALOFT.
ON SMALLER SCALES...CONVECTIVELY INDUCED/REINFORCED MID-UPPER LEVEL
VORTICITY LOBE...APPARENTLY EMBEDDED WITHIN TSTM CLUSTER OVER SRN
GULF OF CA THAT HAS BEEN SHEARED AWAY FROM RESIDUAL LOW LEVEL
CIRCULATION OF TD OLAF. MOST MODELS CONTINUE TO RESOLVE THIS
FEATURE BUT WITH TIMING DIFFERENCES IN ITS DOWNSTREAM PASSAGE ACROSS
S TX...SOMETIME DURING DAYLIGHT HOURS. LOW-AMPLITUDE SHORTWAVE
TROUGH -- EVIDENT IN TIME SERIES OF PLANAR VWP DATA OVER MID/UPPER
TX COAST ATTM...WILL MOVE ACROSS LA COAST EARLY IN PERIOD.
MEANWHILE...LOW-LEVEL BAROCLINIC ZONE -- NOW ANALYZED FROM NEAR COT
ACROSS TX COASTAL BEND...OFFSHORE UPPER TX COAST AND WRN LA...AND
ACROSS SERN LA -- IS FCST TO LIFT NWD AS WARM FRONT ACROSS PORTIONS
SRN/CENTRAL TX AND SRN LA. WEAK FRONTAL-WAVE LOW LAY DEVELOP OVER
SE TX OR SWRN LA AS SRN-STREAM/MID-UPPER LEVEL PERTURBATION APCHS.
WRN SEGMENT OF WARM FRONT WILL RETREAT FARTHER NWD ACROSS RIO GRANDE
VALLEY AND SW TX...WHILE BECOMING MORE DIFFUSE AMIDST
BROAD/LOW-LEVEL WAA REGIME.
...S-CENTRAL/SE TX...SRN LA...
CONSIDERABLE UNCERTAINTY EXISTS REGARDING EXTENT OF NWD MOTION OF
WARM FRONT...GIVEN LIKELIHOOD OF EXTENSIVE CONVECTION AND PRECIP TO
ITS N FOR MUCH OF PERIOD. WEAK TROUGH ALOFT NOW OVER MID/UPPER TX
COAST MAY AID IN MAINTAINING FAVORABLE ENVIRONMENT FOR CONVECTION
OFFSHORE UPPER TX COAST AND LA EARLY IN PERIOD AND DELAY NWD FRONTAL
RETREAT OVER THERE. LAPSE RATES ALOFT GENERALLY SHOULD REMAIN
MRGLLY UNSTABLE...AS MESOSCALE/WEAK DPVA REGIONALLY COUNTERACTS
BROADER STABILIZING EFFECTS ALOFT FROM SYNOPTIC HEIGHT RISES AND
PLUME OF TROPICAL MID-UPPER AIR ADVECTING FROM NWRN MEX.
LOW-LEVEL THERMODYNAMICS WILL REMAIN FAVORABLE WITHIN AND S OF SFC
FRONTAL ZONE...WITH DEW POINTS COMMONLY IN 70S AND SFC HEATING OVER
LAND AREAS REMOVED FROM CLOUD COVER. MLCAPE 2000-3000 J/KG MAY
DEVELOP ALONG AND JUST S OF EFFECTIVE FRONT. PRIND BOUNDARY WILL
NOT RETREAT NWD AS FAST AS FAVORABLE MID-UPPER WINDS OVER REGION.
THIS EFFECT SHOULD MAKE SUPERCELL POTENTIAL
SHORT-LIVED...HEAVY-PRECIP IN MODE...AND TORNADO THREAT VERY MRGL
AND CONDITIONAL ON BOUNDARY INTERACTIONS. ISOLATED STG/DAMAGING
GUSTS ALSO ARE POSSIBLE FROM MOST INTENSE CELLS.
...SRN HIGH PLAINS...AFTER 5/06Z...
WIDELY SCATTERED TO SCATTERED TSTMS MAY DEVELOP LATE IN PERIOD
WITHIN SWATH FROM W-CENTRAL TX NWD ACROSS PORTIONS NW TX AND
PANHANDLE. NARROW...LARGELY MERIDIONAL PLUME OF VIGOROUS MOIST
ADVECTION/TRANSPORT IS FCST WITHIN BROADER LOW LEVEL WAA ZONE. AS
THETAE INCREASES WITHIN 30-40 KT LLJ OVERNIGHT...INCREASINGLY MOIST
PARCELS MAY BE LIFTED ISENTROPICALLY TO LFC. FCST VERTICAL SHEAR
PROFILE IS FAVORABLE FOR AT LEAST MRGL STORM ORGANIZATION...WITH
PROGGED EFFECTIVE SHEAR VARYING FROM 30-35 KT RANGE FOR SHALLOW/WEAK
MUCAPES TO NEAR 500 J/KG...AS PROGGED BY MOST MODELS...TO 50-60 KT
RANGE FOR VERY DEEP MUCAPES 1000-1500 J/KG PER ETA-KF. MOST
AGGRESSIVE PROGS SUGGEST POTENTIAL FOR HAIL WITH MOST INTENSE
CONVECTION...DESPITE MEAGER MID-UPPER LAPSE RATES.
HOWEVER...POTENTIAL APPEARS TOO CONDITIONAL ATTM TO ASSIGN AOA
5-PERCENT UNCONDITIONAL PROBABILITIES FOR LAST FEW HOURS OF PERIOD.
..EDWARDS/GARNER.. 10/04/2009
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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