DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 191258
SWODY1
SPC AC 191256

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0656 AM CST THU DEC 19 2013

VALID 191300Z - 201200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
PATTERN TRANSITION TOWARD WRN CONUS MEAN TROUGH WILL CONTINUE
THROUGH PERIOD. MAIN DRIVER FOR THIS CHANGE IS STG SHORTWAVE TROUGH
-- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY FROM NRN ROCKIES ACROSS
NRN CA TO WATERS OFFSHORE CENTRAL CA COAST. THIS PERTURBATION WILL
CONTINUE TO DIG SSEWD...FORMING CLOSED LOW OVER SRN CA COAST/CHANNEL
ISLANDS AREA BY 00Z. BY 12Z...RESULTING 500-MB CYCLONE SHOULD BE
CENTERED OVER NERN BAJA/NWRN GULF OF CA AREA...S OF YUM...WITH
ASSOCIATED VORTEX COVERING PARTS OF NWRN MEX...SRN CA AND SRN AZ AS
WELL. LARGE DOWNSTREAM FETCH OF SWLY FLOW ALOFT IS EXPECTED TO
DEVELOP BY LATTER PART OF PERIOD...COVERING SRN ROCKIES...SRN
PLAINS...GULF COAST...DIXIE...AND LOWER-MID MS VALLEY. VERY MINOR
PERTURBATIONS MAY BE EMBEDDED WITHIN THAT SWLY FLOW BELT...HOWEVER
PRIMARY AREAS OF DCVA AND HEIGHT FALLS WILL REMAIN JUST AHEAD OF
AZ/NWRN MEX VORTEX.

TIGHTENING SWLY HEIGHT GRADIENT ALOFT WITH SUBSTANTIAL COMPONENT OF
MID-UPPER WINDS ORTHOGONAL TO CENTRAL/SRN ROCKIES IS EXPECTED. THIS
WILL LEAD TO STRENGTHENING OF LOW-LEVEL LEE TROUGHING THROUGH MUCH
OF PERIOD...UNTIL THAT REGIME IS OVERTAKEN FROM N-S BY COLD FRONT.
AT 11Z...SFC ANALYSIS SHOWED THAT FRONT FROM LOWER MI SWWD ACROSS
SRN IA/NRN MO...BECOMING WAVY/QUASISTATIONARY SWD ACROSS
NERN/CENTRAL KS THROUGH DIFFUSE AREA OF LOW PRESSURE OVER SWRN
KS...SERN CO AND OK PANHANDLE. LEE TROUGH EXTENDS FROM THAT AREA
SSWWD ACROSS TX PANHANDLE TO TRANS-PECOS REGION. PLAINS PORTION OF
FRONT SHOULD REMAIN NEAR CURRENT LOCATION THROUGH ABOUT 00Z...THEN
MOVE SWD TO SEWD TOWARD 12Z POSITION NEAR STL-ADM-LBB ARC.

...SWRN CONUS NEAR MID-UPPER LEVEL CYCLONE...
MID-UPPER LEVEL CYCLONE WILL ENGENDER TWO THUNDER-SUPPORTING REGIMES
WITH SOME SPATIAL OVERLAP POSSIBLE ACROSS EXTREME SRN CA.
1. COLD-CORE CONVECTIVE POTENTIAL OVER SRN CA COAST AND ADJACENT
WATERS...AS LARGE-SCALE ASCENT/COOLING ALOFT OCCURS. THIS SHOULD
STEEPEN LOW-MIDDLE LEVEL LAPSE RATES OVER MARINE AIR ENOUGH TO YIELD
100-200 J/KG MUCAPE WITH LITTLE CINH...EXTENDING INTO FAVORABLE
THERMAL LAYERS FOR LTG PRODUCTION...UNDER AND JUST AHEAD OF MIDLEVEL
CYCLONE CENTER.
2. LOW-LEVEL WAA CONVEYOR STRENGTHENS WITH TIME THIS EVENING AND
OVERNIGHT...WHILE SHIFTING EWD FROM SERN CA ACROSS WRN/SRN AZ. SOME
TRAJECTORIES EMANATING FROM SUBTROPICAL PAC WILL BE
POSSIBLE...BOOSTING THETAE IN JUXTAPOSITION WITH ERN RIM OF COOLING
ALOFT. NET RESULT SHOULD BE WEAKLY INHIBITED MUCAPE 100-200
J/KG...WITH SOME ADDITIONAL LIFT POSSIBLE FROM FRONTOGENETIC
FORCING.

...ARKLATEX TO OZARKS/LOWER OH VALLEY...
LOW-LEVEL MOISTURE IS FCST TO INCREASE ACROSS THIS REGION THROUGH
OVERNIGHT HOURS WITHIN IMMATURE/PREFRONTAL RETURN-FLOW
REGIME...AIDED BY 45-55 KT LLJ. PLANAR PROGS AND TIME SERIES OF
FCST SOUNDINGS SHOW MOST CONVECTIVELY AGGRESSIVE MODELS...SUCH AS
NMM MEMBERS OF SREF...BOOSTING LOW-LEVEL THETAE AND REMOVING BASAL
EML CINH ENOUGH TO GENERATE MINIMALLY INHIBITED/ELEVATED CAPE VERY
NEAR END OF PERIOD. HOWEVER...THESE OUTLIER SOLUTIONS STILL OFFER
JUST ISOLATED/BRIEF WINDOW OF LTG RISK AROUND 12Z. AS SUCH...WILL
DEFER OUTLOOK-JUSTIFYING UNCONDITIONAL TSTM PROBABILITIES TO DAY-2
PERIOD.

..EDWARDS/MARSH.. 12/19/2013

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