DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 210602
SWODY1
SPC AC 210600

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1200 AM CST SUN FEB 21 2010

VALID 211200Z - 221200Z

...NO SVR TSTM AREAS FORECAST...

...SRN PLAINS...
A FAST-MOVING UPPER-LEVEL TROUGH WILL MOVE ACROSS THE SRN PLAINS
TODAY WITH A 35 TO 45 KT LOW-LEVEL JET LOCATED AHEAD OF THE SYSTEM
FROM NORTH TX NNEWD INTO CNTRL OK. SCATTERED ELEVATED THUNDERSTORMS
ASSOCIATED WITH WARM ADVECTION SHOULD BE ONGOING THIS MORNING ALONG
THE WEST EDGE OF THE LOW-LEVEL JET. INCREASING LARGE-SCALE ASCENT
FROM WEST TO EAST AHEAD OF THE UPPER-LEVEL TROUGH WILL HELP THE
CONVECTION TO GRADUALLY EXPAND EWD ACROSS OK AND THE REMAINDER OF
NORTH TX THIS MORNING REACHING THE ARKLATEX THIS AFTERNOON. FORECAST
SOUNDINGS ALONG THIS CORRIDOR FROM 18Z TO 21Z KEEP A SFC INVERSION
PRESENT SUGGESTING THE CONVECTION WILL REMAIN ELEVATED EVEN AS SFC
TEMPS WARM SOMEWHAT DURING THE DAY. FORECAST SOUNDINGS SHOW STRONG
EFFECTIVE SHEAR WITH STEEP MID-LEVEL LAPSE RATES AND COLD TEMPS
ALOFT SUGGESTING A MARGINAL POTENTIAL FOR HAIL WILL EXIST.

...LOWER MS VALLEY...
AN UPPER-LEVEL TROUGH OVER THE SRN PLAINS WILL MOVE INTO THE
ARKLATEX THIS AFTERNOON AS A MOIST AXIS SHIFTS EWD FROM SRN PLAINS
INTO THE LOWER MS VALLEY. THE LIKELIHOOD FOR SFC-BASED CONVECTION
WILL INCREASE AS SFC TEMPS WARM THIS AFTERNOON WITH THE MODELS
DEVELOPING SCATTERED THUNDERSTORMS IN EAST TX EARLY THIS AFTERNOON
AND MOVING THIS ACTIVITY EWD ACROSS LA INTO WRN MS BY LATE
AFTERNOON. FORECAST SOUNDINGS IN SCNTRL LA THIS AFTERNOON SHOW SFC
DEWPOINTS INTO THE UPPER 50S F AND MUCAPE VALUES OF ABOUT 1000 J/KG.
THIS COMBINED WITH MODERATE VERTICAL SHEAR PROFILES ASSOCIATED WITH
A MID-LEVEL JET IN THE BASE OF THE UPPER-LEVEL TROUGH MAY SUPPORT AN
ISOLATED SEVERE THREAT THIS AFTERNOON. ALTHOUGH MID-LEVEL LAPSE
RATES ARE NOT FORECAST TO BE THAT STEEP...COLD MID-LEVEL TEMPS ALONG
WITH 45 TO 55 KT OF 0-6 KM SHEAR SHOULD BE ENOUGH FOR HAIL WITH THE
STRONGER UPDRAFTS. SFC-BASED THUNDERSTORMS MAY ALSO HAVE A MARGINAL
WIND DAMAGE THREAT ESPECIALLY IN SRN LA WHERE FORECAST SOUNDING SHOW
THE STEEPEST LOW-LEVEL LAPSE RATES. ALTHOUGH A FEW ROTATING STORMS
ARE POSSIBLE...VEERED LOW-LEVEL WIND PROFILES SHOULD KEEP ANY
TORNADO THREAT MARGINAL THIS AFTERNOON.

..BROYLES.. 02/21/2010

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