MESOSCALE DISCUSSION 2215
NWS STORM PREDICTION CENTER NORMAN OK
1212 PM CST TUE DEC 08 2009
AREAS AFFECTED...PARTS OF LA INTO SWRN AND CENTRAL MS
CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY
VALID 081812Z - 081945Z
SEVERE/TORNADO THREAT CONTINUES TO SLOWLY INCREASE ACROSS THE LOWER
MS VALLEY REGION. A TORNADO WATCH WILL LIKELY BE REQUIRED IN THE
NEXT 1-2 HOURS.
A POWERFUL STORM SYSTEM CONTINUES MOVING OUT OF THE ROCKIES AND INTO
THE CENTRAL U.S. THIS AFTERNOON...WITH STRONG ASCENT -- HIGHLIGHTED
BY STRONG PRESSURE FALLS FROM MO SWD INTO LA ATTM -- CONTINUING TO
OVERSPREAD THE CENTRAL CONUS.
MOST OF THE DEVELOPING CONVECTION REMAINS ELEVATED ATTM FROM NRN LA
NWD...WHERE A COOL/STABLE BOUNDARY LAYER PERSISTS.
HOWEVER...MOISTENING/DESTABILIZING AIRMASS CONTINUES TO SPREAD NWD
WITHIN STRONG SLY LOW-LEVEL FLOW FIELD ACROSS THE LOWER MS VALLEY
REGION...WITH SURFACE LOW DEVELOPMENT UNDERWAY INVOF ERN OK/WRN AR
AND VICINITY. AS MOISTENING/DESTABILIZING CONTINUES...SURFACE-BASED
CONVECTION -- NOW SHOWING INITIAL SIGNS OF DEVELOPMENT OVER SRN LA
-- SHOULD SLOWLY INCREASE WITHIN BROAD ZONE OF WARM ADVECTION OVER
THE LOWER MS VALLEY.
AREA VWPS REVEAL LOW-LEVEL SLYS/SELYS WHICH VEER/INCREASE QUICKLY
WITH HEIGHT...YIELDING FAVORABLE SHEAR FOR ORGANIZED/ROTATING
STORMS. AS AIRMASS CONTINUES TO BECOME MORE SUPPORTIVE OF SUSTAINED
DEEP CONVECTION WITH TIME...AND AS FLOW ALOFT INCREASES WITH THE
APPROACH OF THE UPPER SYSTEM...SUPERCELLS ARE EXPECTED TO EVOLVE
THROUGH THIS AFTERNOON. AS SEVERE/TORNADO POTENTIAL SLOWLY
INCREASES...TORNADO WATCH WILL LIKELY BECOME NECESSARY -- INITIALLY
OVER PARTS OF LA AND INTO CENTRAL AND SRN MS.
..GOSS.. 12/08/2009
