SWODY1
SPC AC 030540
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1240 AM CDT SAT OCT 03 2009
VALID 031200Z - 041200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
PROGRESSIVE UPPER AIR PATTERN -- CHARACTERIZED BY CLOSED CYCLONES --
WILL CONTINUE ACROSS CONUS THROUGH PERIOD...BUT WITH INCREASING
RELATIVE EMPHASIS TOWARD WRN HEIGHT FALLS. MID-UPPER VORTEX NOW
CENTERED INVOF WI/IL BORDER IS FCST TO CONTINUE FILLING AND TO PIVOT
NNEWD ACROSS UPPER GREAT LAKES AND OVER NRN ONT. SHORTWAVE TROUGH
NOW TRAILING SWD ACROSS WRN IL WILL LIFT ENEWD UP OH VALLEY AND
ACROSS LOWER GREAT LAKES. ALTHOUGH THIS FEATURE WILL LOSE AMPLITUDE
WITH TIME...IT SHOULD TIGHTEN HEIGHT GRADIENT OVER MID-ATLANTIC
REGION DURING DAY. MEANWHILE...SECOND UPPER LOW -- NOW EVIDENT IN
MOISTURE CHANNEL IMAGERY OVER SRN BC -- WILL DIG SWD ACROSS INTERIOR
PACIFIC NW...DEEPENING AND REACHING NRN GREAT BASIN BY 4/12Z.
AT SFC...FRONTAL ZONE TRAILING FROM UPPER MIDWEST CYCLONE IS STALLED
ACROSS EXTREME NWRN GULF AND PORTIONS DEEP S TX. WRN SEGMENT OF
THIS BOUNDARY SHOULD BECOME MORE DIFFUSE AND RETREAT NWD ACROSS S TX
AS WARM FRONT THROUGHOUT PERIOD...DELAYED/RESHAPED ON MESOSCALE BY
AREAS OF CONVECTIVE PRECIP TO ITS N. ERN FRONTAL SEGMENT IS FCST TO
MOVE EWD ACROSS MID-ATLANTIC AND WRN NEW ENGLAND THROUGH PERIOD.
...MID-ATLANTIC AND SRN NEW ENGLAND...
CONDITIONAL/MULTIMODAL SVR THREAT EXISTS AHEAD OF COLD FRONT OVER
THIS REGION...IN PARALLEL ZONE OF LOW LEVEL CONVERGENCE...JUXTAPOSED
WITH STRENGTHENING FLOW ALOFT ASSOCIATED WITH EJECTING OH VALLEY
SHORTWAVE TROUGH. DURING MOST OF LATE MORNING THROUGH LATE
AFTERNOON...FCST SOUNDINGS ACROSS THIS REGION INDICATE NEARLY
UNCAPPED BOUNDARY LAYER AIR MASS...WITH AT LEAST MRGL BUOYANCY.
FAVORABLE DEEP-LAYER SHEAR IS EXPECTED -- E.G. 40-55 KT EFFECTIVE
SHEAR MAGNITUDES THAT VARY WITH AMOUNT/DEPTH OF CAPE. SLGT BACKING
OF SFC FLOW IN AND E OF CONVERGENCE ZONE WILL CONTRIBUTE MOIST
ADVECTION/TRANSPORT AS WELL AS SOME ENLARGEMENT OF LOW LEVEL
HODOGRAPHS. ATTM...CONCERNS ABOUT EXTENT OF DESTABILIZATION BEHIND
MORNING CLOUDS/PRECIP PRECLUDE UNCONDITIONAL PROBABILITIES
SUFFICIENT FOR CATEGORICAL OUTLOOK.
...S AND CENTRAL TX...
ONE OR TWO CLUSTERS OF STG...PERHAPS MRGL SVR TSTMS ARE POSSIBLE
ACROSS PORTIONS CENTRAL/S TX EARLY IN PERIOD. THIS ACTIVITY IS
EXPECTED AS ISENTROPIC ASCENT TO LFC OCCURS N OF SFC FRONT...IN
REGIME OF INCREASING LOW LEVEL MOISTURE AND FAVORABLE EFFECTIVE
SHEAR ALOFT. THIS REPRESENTS EXTENSION OF REGIME FROM END OF PRIOR
PERIOD...FOR WHICH MRGL UNCONDITIONAL HAIL PROBABILITIES ALREADY ARE
OUTLOOKED. PRIMARY FACTORS PRECLUDING CATEGORICAL OUTLOOK ATTM
INCLUDE UNCERTAINTIES REGARDING POSITION OF ELEVATED CONVECTIVE
INITIATION AND INTENSIFICATION...AS WELL AS PRESENCE OF RELATIVELY
WEAK MIDLEVEL LAPSE RATES THAT WILL LIMIT BUOYANCY AND POTENTIAL FOR
LARGER HAIL.
MID-UPPER LEVEL CLOUDS AND MOISTURE STREAMING OFF PACIFIC TS OLAF
MAY SOMEWHAT RESTRAIN DIABATIC HEATING WITHIN AND ALONG WARM SIDE OF
FRONTAL ZONE DURING AFTERNOON...AND MOST LIKELY WILL YIELD WEAK
UPPER LEVEL LAPSE RATES. STILL...DIFFERENTIAL HEATING ACROSS
BOUNDARY MAY CONTRIBUTE TO ADDITIONAL/SFC-BASED/DIURNAL DEVELOPMENT
INVOF FRONTAL ZONE...AND BENEATH SRN RIM OF UPPER LEVEL JET MAX TO
ENHANCE CLOUD-LAYER SHEAR. ANY STG-SVR GUSTS SHOULD OCCUR IN AND S
OF FRONTAL ZONE...WHILE HAIL SIZE SHOULD BE MRGL SVR...AT
BEST...ANYWHERE OVER REGION.
..EDWARDS/GARNER.. 10/03/2009
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