Friday, March 27, 2009

SPC Upgrades Risk to Moderate


SPC Tornado Outlook


SPC Day One

   DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0723 AM CDT FRI MAR 27 2009

VALID 271300Z - 281200Z

...THERE IS A MDT RISK OF SVR TSTMS OVER FAR NERN TX...NRN LA...SRN
AR...CENTRAL MS...

...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF THE SRN PLAINS
ACROSS THE CENTRAL GULF COAST STATES...

...SRN PLAINS ACROSS LOWER MS VALLEY/CNTRL GULF COAST STATES...
INTENSE MID/UPPER LEVEL LOW DIGGING SSEWD ACROSS CO/NRN NM EARLY
THIS MORNING WILL BEGIN TO TURN MORE ELY BY LATE TODAY AS 100+ KT
MID LEVEL JET BEGINS TO ROTATE THROUGH BASE OF TROUGH. ASSOCIATED
SURFACE LOW NOW DEEPENING OVER NWRN TX WILL LIKEWISE DEVELOP ENEWD
ACROSS THE ARKLATEX REGION BY THE EARLY EVENING AND INTO THE MID
SOUTH OVERNIGHT. COMPLEX WARM SECTOR IS IN PLACE AHEAD OF THIS
INTENSE SPRING-TIME SYSTEM DUE TO EXTENSIVE CONVECTION THURSDAY AND
ASSOCIATED OUTFLOW BOUNDARY EXTENDING ALONG THE CENTRAL GULF COAST
INTO DEEP SOUTH TX. RICHEST GULF MOISTURE IS BEING CONTAINED SOUTH
OF THIS FEATURE EARLY THIS MORNING. HOWEVER AS PRESSURE FALLS
INCREASE OVER ERN PORTIONS OF THE SRN PLAINS...EXPECT GRADUAL
RECOVERY/NWD ADVECTION OF RICHER GULF MOISTURE THROUGH THE
DAY...ESPECIALLY OVER ERN TX/WRN-CENTRAL LA. AS OUTFLOW BOUNDARY
ERODES...EFFECTIVE WARM FRONT IS EXPECTED TO BECOME ESTABLISHED MORE
W-E FROM NERN TX ACROSS SRN AR/NRN LA INTO CENTRAL/SERN MS. GIVEN
STEEP LAPSE RATES ALOFT ALREADY IN PLACE AS EVIDENCED BY 12Z
SOUNDINGS AND AT LEAST MODEST HEATING...AIR MASS SHOULD BECOME
MODERATELY UNSTABLE OVER MUCH OF THE DEVELOPING WARM SECTOR...WITH
MARGINAL INSTABILITY REACHING NWWD INTO PORTIONS OF OK/AR.

/EARLY DAY THREATS/
REFERENCE LATEST SWOMCD AND/OR WATCHES FOR THESE AREAS.

ONGOING...LONG-LIVED LINEAR MCS SHOULD GRADUALLY DIMINISH AS IT
INGESTS DRIER/MORE STABLE AIR OVER NRN FL/GA. ALTHOUGH OFFSHORE
COMPONENT OF THIS LINE MAY REMAIN INTENSE THROUGH THE MORNING ALONG
THE FL PANHANDLE COAST INTO THE NERN GOM. AN ISOLATED TORNADO
AND/OR WIND DAMAGE MAY ACCOMPANY THIS ACTIVITY EARLY TODAY NEAR THE
COAST.

ELEVATED THUNDERSTORMS ALREADY NEAR SVR LEVELS OVER WRN/CENTRAL OK
WILL LIKELY INCREASE IN COVERAGE THROUGH THE MORNING/AFTERNOON
ACROSS MORE OF OK/NRN TX. ALTHOUGH ACTIVITY WILL BE HIGHLY
ELEVATED...FORECAST SOUNDINGS SUGGEST STEEP LAPSE RATES...MODEST
MUCAPE AND SUFFICIENT EFFECTIVE SHEAR WHICH WILL SUPPORT POTENTIAL
FOR LARGE HAIL.

/MID-LATE DAY THROUGH TONIGHT/
MODELS ARE IN ALMOST COMPLETE AGREEMENT IN GENERATING THUNDERSTORMS
AHEAD OF FAST MOVING COLD FRONT OVER ERN TX BETWEEN 18-21Z. THIS
ACTIVITY WILL BE SURFACE-BASED AND DEVELOP WITHIN MODERATE MLCAPE
AND STEEP MID LEVEL LAPSE RATES. EXPECT THESE STORMS WILL CONTINUE
TO INCREASE IN BOTH COVERAGE AND INTENSITY ACROSS MUCH OF LA/SRN AR
THROUGH THE EVENING...OVERSPREADING THE LOWER MS RIVER VALLEY LATE
THIS EVENING/OVERNIGHT. DEEP LAYER SHEAR WILL REMAIN QUITE STRONG
ACROSS THE REGION THROUGHOUT THE PERIOD...DESPITE GENERAL BACKING OF
MID LEVEL FLOW IN TIME TO A MORE SLY DIRECTION AS DEEP/CLOSED LOW
PROGRESSES EWD. MEANWHILE...LOW LEVEL SHEAR SHOULD INTENSIFY LATE
TODAY/THIS EVENING ALONG AXIS OF STRENGTHENING LLJ.

CONVECTIVE-MODE REMAINS SOMEWHAT UNCERTAIN AS COMPETING INFLUENCES
OF INTENSE DEEP LAYER SHEAR AND STRONG DOWNSHEAR COMPONENT OF
STORM-RELATIVE WINDS ALOFT SUGGEST LONGER-LIVED SUPERCELLS...WHILE
FAST MOTION OF N-S ORIENTED COLD FRONT MAY INHIBIT STORMS FROM
MOVING OFF INITIATING BOUNDARY. THIS COULD FORCE A LARGE QLCS WITH
EMBEDDED LEWPS/SUPERCELLS QUICKLY EWD THROUGH TONIGHT WITH POSSIBLE
WIDESPREAD WIND DAMAGE AND TORNADOES /SOME OF WHICH COULD BE
STRONG/. TORNADO POTENTIAL WILL BE MOST PRONOUNCED INVOF THE
SURFACE WARM FRONT/LOW CENTER...ALTHOUGH ANY PRECEEDING DEVELOPMENT
WITHIN BROAD WARM SECTOR WOULD LIKELY REMAIN DISCRETE WITH ATTENDANT
TORNADO THREAT. STEEP LAPSE RATES WILL ALSO SUPPORT LARGE HAIL OVER
A LARGE PART OF THE SRN PLAINS EWD ACROSS THE MID SOUTH/CENTRAL GULF
COAST STATES THROUGH THE PERIOD...WITH LARGEST HAIL /POSSIBLY
EXCEEDING 2 INCHES IN DIAMETER/ EXPECTED AS INITIAL SUPERCELLS
DEVELOP OVER ERN TX/WRN LA IN STRONGEST INSTABILITY THIS
AFTERNOON/EARLY EVENING.

..EVANS/GARNER.. 03/27/2009

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