DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 151247
SWODY1
SPC AC 151245

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0645 AM CST SAT DEC 15 2012

VALID 151300Z - 161200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
IN MID-UPPER LEVELS...SEVERAL SHORTWAVES ARE FCST TO TRAVERSE BELT
OF CYCLONIC FLOW ASSOCIATED WITH WRN CONUS MEAN TROUGH. FIRST OF
THESE...NOW MANIFEST AS CLOSED 500-MB CYCLONE OVER NRN MO/SRN IA
REGION -- WILL MOVE NEWD TO LH BY 16/12Z AND WEAKEN CONSIDERABLY.
UPSTREAM SHORTWAVE TROUGH -- CURRENTLY OVER SRN PORTIONS NV/CA -- IS
EXPECTED TO PIVOT GENERALLY EWD ACROSS NRN AZ BY EARLY
EVENING...REACHING TX PANHANDLE BY 16/12Z. WEAKER AND INITIALLY
SEPARATE PERTURBATION -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
OVER PAC NEAR 30N120W -- SHOULD MOVE EWD ACROSS CENTRAL BAJA AROUND
00Z...THEN ESSENTIALLY PHASE WITH MORE NRN FEATURE....REACHING SW TX
AROUND 16/12Z.

SFC CYCLONE -- ANALYZED AT 15/12Z BETWEEN HSI-LNK -- IS FCST TO
EJECT ENEWD ACROSS IA TO UPPER MS VALLEY...REACHING SERN MN BY 00Z
AND WRN LS/WRN UPPER MI REGION NEAR END OF PERIOD. TRAILING PAC
COLD FRONT -- FROM ERN PORTIONS KS/OK INTO S-CENTRAL TX THIS MORNING
-- SHOULD BECOME QUASISTATIONARY NEAR OR JUST SE OF PRESENT
POSITION...WHILE AWAITING ARRIVAL OF REINFORCING CAA/BAROCLINICITY
PRECEDING AFOREMENTIONED LATE-PERIOD SHORTWAVES. SLGT NWWD DRIFT OF
THIS BOUNDARY ALSO IS POSSIBLE AFTER 06Z...PARTICULARLY WHERE NO
BAROCLINICALLY REINFORCING PRECIP HAS DEVELOPED BY THEN.

...PORTIONS LA...UPPER TX COASTAL PLAIN...
ONGOING THIN BAND OF CONVECTION WILL CONTINUE SHIFTING EWD ACROSS
ARKLATEX REGION AND SLOWLY SEWD OVER MID-UPPER TX COASTAL
PLAIN...WITH GEN WEAKENING TREND THROUGH REMAINDER OF MORNING.

GREATEST TSTM POTENTIAL OVER THIS REGION WILL BE WIDELY SCATTERED
COVERAGE OVERNIGHT...ESPECIALLY DURING LAST 3-6 HOURS OF PERIOD AS
SUBTLE LARGE-SCALE ASCENT RELATED TO CA/PAC SHORTWAVES APCHS FRONTAL
ZONE. THIS SHOULD COMBINE WITH SUFFICIENT THETAE TO OFFSET WEAK
MID-UPPER LEVEL LAPSE RATES...RESULTING IN 500-1000 J/KG MUCAPE AND
WEAKENING OF PREVIOUSLY STOUT LOW-LEVEL CAPPING DURING 09-12Z TIME
FRAME. ALTHOUGH FRONTAL CONVERGENCE WILL REMAIN WEAK...DECREASING
CINH SHOULD SUPPORT INCREASING CONVECTIVE POTENTIAL. HEIGHT
GRADIENTS ALOFT WILL TIGHTEN AHEAD OF SWRN CONUS
SHORTWAVES...RESULTING IN STRENGTHENING DEEP SHEAR ATOP RELATIVELY
WEAK NEAR-SFC WINDS. 50-60 KT EFFECTIVE SHEAR MAGNITUDES ARE
POSSIBLE.

HOWEVER...CONFIDENCE IS NOT VERY STG IN DEVELOPMENT OF GREATER
CONVECTIVE COVERAGE/INTENSITY IN THIS REGIME...GIVEN WEAK LAPSE
RATES ALOFT...LACK OF MORE ROBUST FLOW/CONVERGENCE IN LOW
LEVELS...AND ERRATIC/INCONSISTENT PRECIP SIGNALS IN
CONVECTION-ALLOWING/SSEO GUIDANCE. ANY SUSTAINED/INTENSE CELLS THAT
DO DEVELOP COULD TRANSFER MOMENTUM TO SFC FROM STG FLOW ALOFT...AND
POSE THREAT OF STG/ISOLATED SVR GUSTS PENETRATING SHALLOW/NEAR-SFC
STABLE LAYER.

..EDWARDS/SMITH.. 12/15/2012

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