DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 241233
SWODY1
SPC AC 241231

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0631 AM CST MON DEC 24 2012

VALID 241300Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS TONIGHT INTO TUESDAY MORNING
ACROSS PORTIONS OF ERN TX AND WRN LA...

...SYNOPSIS...

A SHORTWAVE TROUGH CURRENTLY OVER THE LOWER MS VALLEY WILL RAPIDLY
TRANSLATE EWD ACROSS THE GULF STATES TODAY IN ADVANCE OF
INTENSIFYING MID AND UPPER-LEVEL JET STREAKS WHICH WILL DEVELOP FROM
THE FAR ERN PACIFIC AND CA SEWD INTO THE SRN ROCKIES AND LOWER RIO
GRANDE VALLEY BY 25/12Z. FORCING FOR ASCENT IN THE EXIT REGION OF
THE JET STREAKS COUPLED WITH INCREASING DCVA AHEAD OF AMPLIFYING
COMPANION SHORTWAVE TROUGH WILL RESULT IN A CORRIDOR OF 500-MB
HEIGHT FALLS OF AROUND 100M/12-HR SPREADING SEWD FROM THE SRN
ROCKIES INTO WRN TX LATE TONIGHT INTO TUESDAY MORNING.

IN THE LOW LEVELS...A SURFACE CYCLONE ASSOCIATED WITH THE LOWER MS
VALLEY IMPULSE MENTIONED ABOVE WILL DEVELOP NEWD INTO THE UPPER OH
VALLEY BY THIS EVENING WHILE A TRAILING COLD FRONT SETTLES SEWD TO
THE WRN/CNTRL GULF COAST BEFORE BECOMING STATIONARY TONIGHT.
FARTHER W...LEE CYCLOGENESIS WILL COMMENCE TODAY OVER THE SRN HIGH
PLAINS WITH A DISTINCT LOW PRESSURE CENTER DEVELOPING SEWD FROM NERN
NM INTO CNTRL TX BY 25/12Z. THE PROGRESSION OF THIS FEATURE WILL
RESULT IN THE NWD MOVEMENT OF A WARM FRONT FROM THE TX COASTAL
PLAINS AND SRN LA TO BETWEEN THE I-10 AND I-20 CORRIDORS BY THE END
OF THE D1 PERIOD.

...ERN TX INTO CNTRL/SRN LA TONIGHT...

TEMPORARY HEIGHT RISES IN THE WAKE OF LOWER MS VALLEY DISTURBANCE
WILL STRENGTHEN THE EXISTING CAP AND EFFECTIVELY INHIBIT TSTM
DEVELOPMENT THROUGH THIS AFTERNOON ALONG THE DECELERATING COLD
FRONT. TONIGHT...THE DEVELOPMENT OF A SSWLY LLJ WITHIN THE EXIT
REGION OF THE APPROACHING UPPER-LEVEL JET STREAK WILL ENHANCE THE
NWD FLUX OF AN INCREASINGLY MOIST BOUNDARY LAYER...AND THE POLEWARD
MOVEMENT OF THE SURFACE WARM FRONT. THESE PROCESSES WILL COINCIDE
WITH STEEPENING MIDLEVEL LAPSE RATES...YIELDING RAPID AIR MASS
DESTABILIZATION AFTER SUNSET WITH MUCAPE VALUES APPROACHING
1000-2000 J/KG BY TUESDAY MORNING.

ELEVATED TSTMS ARE EXPECTED TO DEVELOP BY AS EARLY AS 25/02Z-03Z TO
THE NORTH OF THE SURFACE WARM FRONT FROM THE TX HILL COUNTRY INTO
THE SABINE RIVER VALLEY AS LOW-LEVEL MOISTENING/ASCENT GRADUALLY
OVERCOME THE CAP. STORMS ARE EXPECTED INCREASE IN COVERAGE AND
INTENSITY OVERNIGHT AS DEEP-LAYER ASCENT FURTHER STRENGTHENS IN EXIT
REGION OF UPPER-LEVEL JET STREAK. THE PRIMARY HAZARD WILL BE LARGE
HAIL OWING TO THE STEEP LAPSE RATES...COOL MIDLEVEL TEMPERATURE
PROFILES...AND EFFECTIVE BULK SHEAR VALUES OF 40-50 KT.

THE THREAT FOR SURFACE-BASED STORMS...INCLUDING TORNADIC
SUPERCELLS...IS EXPECTED TO INCREASE BETWEEN 25/09Z-12Z ALONG THE
RETREATING WARM FRONT WHERE BOUNDARY LAYER DEWPOINTS IN THE LOW/MID
60S PROMOTE MLCAPE VALUES APPROACHING 1000-1500 J/KG. THIS
INSTABILITY WILL COINCIDE WITH EFFECTIVE SRH VALUES OF 200-300 M2/S2
AND 40-50 KT OF DEEP-LAYER SHEAR...RESULTING IN A FAVORABLE
ENVIRONMENT FOR UPDRAFT SUSTENANCE/ROTATION. DAMAGING WIND
POTENTIAL WILL ALSO INCREASE...ESPECIALLY WITH ANY EVOLVING LINE
SEGMENTS/BOWING STRUCTURES.

...CNTRL/ERN GULF COAST TODAY...

THE STRONGEST FORCING FOR ASCENT/DCVA ASSOCIATED WITH THE LOWER MS
VALLEY SHORTWAVE TROUGH WILL BECOME PROGRESSIVELY DISPLACED FROM A
MOISTENING WARM SECTOR...CHARACTERIZED BY MUCAPE OF 1500-1800 J/KG
PER 12Z LCH/LIX SOUNDINGS. NONETHELESS...LOW-LEVEL CONFLUENT FLOW
COUPLED WITH THE GLANCING INFLUENCE OF THE SHORTWAVE TROUGH WILL
SUSTAIN A MIXTURE OF ELEVATED AND SOME SURFACE BASED STORMS TODAY
WITHIN A WARMING/DESTABILIZING AIR MASS FROM SERN PARTS OF LA/MS
INTO SRN AL AND THE FL PNHDL. FORECAST HODOGRAPHS ACROSS THIS
REGION EXHIBIT VERTICALLY VEERING WIND PROFILES WITH SUFFICIENT
LOW-LEVEL AND DEEP-LAYER SHEAR FOR ROTATING STORMS. AS SUCH...A LOW
PROBABILITY RISK FOR DAMAGING WINDS AND PERHAPS A TORNADO WILL EXIST
WITH ANY SUSTAINED...SURFACE-BASED STORMS.

..MEAD/LEITMAN.. 12/24/2012

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