DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 310552
SWODY1
SPC AC 310550

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1250 AM CDT SUN MAR 31 2013

VALID 311200Z - 011200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF CENTRAL...
SOUTH...AND EAST TX TO THE LOWER MS VALLEY...

...SYNOPSIS...
A POLAR VORTEX WILL ROTATE ESEWD ACROSS ONTARIO TODAY/TONIGHT AND
MAINTAIN A CYCLONIC FLOW REGIME EAST OF THE ROCKIES TO THE ERN U.S.
COAST. WHILE STRONGEST MID AND UPPER LEVEL WINDS WILL EXTEND FROM
THE LEE OF THE CANADIAN ROCKIES THROUGH THE NRN PLAINS TO THE OH
VALLEY AND NERN STATES...MODEST WNWLY FLOW IS EXPECTED FROM THE SRN
PLAINS TO THE GULF COAST REGION. MEANWHILE...THE CLOSED LOW
ASSOCIATED WITH THE ERN PACIFIC REX BLOCK IS EXPECTED TO UNDERGO
SUBSTANTIAL WEAKENING THIS FORECAST PERIOD AS IT SHIFTS EWD ACROSS
CA REACHING NV BY 12Z MON.

AT THE SURFACE...A FRONT EXTENDING FROM AR WSWWD ALONG THE RED RIVER
VALLEY TO THE TX SOUTH PLAINS AT 12Z TODAY WILL MOVE SWD...TENDING
TO WEAKEN AS IT ADVANCES TOWARD S TX...THE LOWER MS VALLEY AND THE
CENTRAL GULF COAST STATES. ONE OR MORE OUTFLOW BOUNDARIES ATTENDANT
TO POTENTIALLY ONGOING CONVECTION/EMBEDDED TSTM COMPLEXES ALONG THE
RED RIVER VALLEY INTO AR AT THE START OF DAY 1 MAY LOCALLY ENHANCE
THE SWD MOVEMENT OF THE AFOREMENTIONED FRONT TODAY.

...CENTRAL/SOUTH/EAST TX TO THE LOWER MS VALLEY...
CONVECTION/EMBEDDED TSTMS ARE EXPECTED TO BE ONGOING AT 12Z TODAY
FROM THE SERN TX PANHANDLE EWD THROUGH SRN OK AND N TX...POTENTIALLY
EXTENDING INTO AR. THE PRESENCE OF STEEP MIDLEVEL LAPSE
RATES...MODERATE INSTABILITY AND EFFECTIVE BULK SHEAR AROUND 40 KT
/ESPECIALLY INVOF THE RED RIVER/ SUGGEST THE POTENTIAL FOR SOME OF
THIS ACTIVITY TO BE SEVERE EARLY SUN MORNING.

A SHORTWAVE TROUGH TRACKING INTO THE BASE OF THE CENTRAL/ERN U.S.
LONGWAVE TROUGH WILL GLANCE THE ARKLATEX REGION...WHILE A SECOND
SHORTWAVE TROUGH...CURRENTLY LOCATED OVER THE SWRN STATES...IS
EXPECTED TO REACH THE TX PORTION OF THE SLIGHT RISK AREA BY LATE
THIS AFTERNOON. SURFACE HEATING ALONG AND S OF THE ONGOING
CONVECTION AND SWD MOVING FRONT WITHIN A MOIST AIR MASS WILL RESULT
IN MODERATE INSTABILITY...GIVEN THE PRESENCE OF STEEP MIDLEVEL LAPSE
RATES /7-8 C PER KM/. DESPITE THE LACK OF STRONGER DEEP LAYER
FORCING FOR ASCENT...NEW TSTM DEVELOPMENT SHOULD OCCUR WITHIN THE
DESTABILIZING ENVIRONMENT AS THE SURFACE FRONT ADVANCES SWD.
EFFECTIVE BULK SHEAR OF 40-50 KT AND STRAIGHT HODOGRAPHS WILL PROVE
FAVORABLE FOR SPLITTING STORMS WITH HAIL AND DAMAGING WINDS THE
PRIMARY THREATS.

THE STRONGEST INSTABILITY SHOULD BE LOCATED WITH WSWWD EXTENT ACROSS
SOUTH CENTRAL TX...WHERE THE POTENTIAL EXISTS FOR STORM DEVELOPMENT
THIS AFTERNOON AND EVENING...BUT OVERALL STORM COVERAGE MAY BE LESS.
STORMS THAT DO DEVELOP IN THIS AREA COULD PRODUCE VERY LARGE HAIL
/EXCEEDING 2 INCH DIAMETER/...BUT CONFIDENCE IN THE OVERALL COVERAGE
OF THIS THREAT PRECLUDES THE INCLUSION OF A SIGNIFICANT HAIL AREA.

...SRN AL AND WRN FL PANHANDLE...
TSTMS WILL BE POSSIBLE FROM THE LOWER MS VALLEY EWD TO THE SERN
STATES. WEAKER MIDLEVEL LAPSE RATES WITH EWD EXTENT INTO THE CENTRAL
GULF COAST REGION WILL TEND TO LIMIT THE DEVELOPMENT OF STRONGER
INSTABILITY. THESE FACTORS COMBINED WITH WEAK EFFECTIVE BULK SHEAR
SHOULD RESULT IN A MINIMAL SEVERE WEATHER THREAT INTO SRN AL AND THE
WRN FL PANHANDLE.

...SACRAMENTO/SAN JOAQUIN VALLEYS...
TSTM DEVELOPMENT IS EXPECTED IN THE CENTRAL VALLEY OF
CA...ESPECIALLY THIS AFTERNOON INTO THE EARLY EVENING. ALTHOUGH
EFFECTIVE BULK SHEAR WILL BE QUITE WEAK LIMITING THE POTENTIAL FOR
STORM ORGANIZATION...500 MB TEMPERATURES /-22 TO -24 C/ AND LOW-MID
LEVEL LAPSE RATES AROUND 7 C/KM SUGGEST SUB-SEVERE HAIL WILL BE
POSSIBLE WITH THE STRONGER ACTIVITY.

..PETERS/DEAN.. 03/31/2013

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