DAY 1 CONVECTIVE OUTLOOK

Forecast Discussion
SPC AC 190043

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0743 PM CDT TUE MAR 18 2008

VALID 190100Z - 191200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVERNIGHT FOR THE LOWER MS
VALLEY REGION...

...LOWER MS VALLEY OVERNIGHT...
SURFACE ANALYSES CONFIRM THE CONSOLIDATION OF A 997 MB LOW NEAR TYR
IN NE TX. THIS LOW WILL TRANSLATE NEWD OVERNIGHT ACROSS AR TO WRN
TN ALONG A QUASI-STATIONARY FRONT...AND IN ADVANCE OF THE EJECTING
MID LEVEL SHORTWAVE TROUGH AND ASSOCIATED 100 KT 500 MB SPEED MAX
FROM CENTRAL/S TX. S OF THE LOW...A REMNANT DRYLINE IS BEING
OVERTAKEN BY THE SURFACE COLD FRONT...AND THIS FRONT WILL MOVE EWD
ACROSS E TX/LA/MS BY THE END OF THE PERIOD.

PRE-FRONTAL CONVECTION HAS BEEN SLOW TO DEVELOP DURING THE DAY IN
THE WARM SECTOR...WITH RELATIVELY WEAK/ELEVATED CONVECTION IN A
LOOSE BAND FROM NW LA INTO SW AR. THIS CONVECTION HAS STRUGGLED TO
ACQUIRE SUPERCELL CHARACTERISTICS...LIKELY DUE TO THE ORIGINATION OF
THE UPDRAFTS JUST ABOVE THE LAYER OF STRONGEST VERTICAL SHEAR FROM
THE SURFACE TO 850 MB. OTHERWISE...THE VAST MAJORITY OF THE
THUNDERSTORMS HAVE BEEN CONFINED TO THE COOL SIDE OF THE SURFACE
BAROCLINIC ZONES IN AN ANAFRONTAL FLOW REGIME. SOME EWD
ACCELERATION OF THE COLD FRONT IS EXPECTED TONIGHT ACROSS
LA/MS...AND A NARROW BAND OF STORMS SHOULD STILL REMAIN TIED TO THE
FRONT THROUGH THE PERIOD. MEANWHILE...SOME INCREASE IN LOW-LEVEL
MOISTURE IS EXPECTED TONIGHT AS 64-67 F BOUNDARY LAYER DEWPOINTS
SPREAD NWD FROM SE LA INTO CENTRAL MS. POOR MID LEVEL LAPSE RATES
WILL LIMIT THE ABSOLUTE MAGNITUDE OF THE INSTABILITY...THOUGH THE
MOISTURE INCREASE SHOULD ALLOW CONVECTION TO BE BASED VERY NEAR THE
GROUND.

VERY STRONG LOW-MID LEVEL WINDS /UP TO 70 KT SSWLY FLOW AT BOTH 850
MB AND 500 MB/ WILL CONTRIBUTE TO VERTICAL SHEAR PROFILES WITH
STRONG LOW-LEVEL SHEAR /EFFECTIVE SRH IN EXCESS OF 500 M2/S2/...BUT
DEEP LAYER VERTICAL SHEAR LARGELY PARALLEL TO THE FRONT. SUCH A
CONFIGURATION SUPPORTS A NARROW FORCED LINE OF STORMS ALONG THE
FRONT...WITH SOME EMBEDDED SUPERCELL AND/OR BOWING SEGMENTS AND AN
ATTENDANT THREAT FOR DAMAGING WINDS AND A COUPLE OF TORNADOES. MORE
DISCRETE SUPERCELL STRUCTURES MAY ALSO OCCUR ALONG THE BAROCLINIC
ZONE ACROSS SRN AR WHERE THE LOOSE BAND OF ELEVATED CONVECTION
INTERACTS WITH THE FRONT. STILL...A SERIES OF SHORT N-S BOWING
SEGMENTS PROPAGATING NEWD ALONG THE FRONT SHOULD REMAIN THE DOMINANT CONVECTIVE MODE THIS AREA.

..THOMPSON.. 03/19/2008