SWODY1
SPC AC 170541
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1141 PM CST MON FEB 16 2009
VALID 171200Z - 181200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF FAR ERN
TX...NRN LA...AR...MS...TN AND NRN AL...
...LOWER MS AND TN VALLEYS...
A FLAT UPPER-LEVEL RIDGE OVER THE CNTRL U.S. WILL MOVE QUICKLY EWD
TODAY AS AN UPPER-LEVEL TROUGH REPLACES THE RIDGE OVER THE PLAINS
STATES. A 50 TO 60 KT LOW-LEVEL JET WILL STRENGTHEN AHEAD OF THE
DEVELOPING TROUGH OVER THE LOWER MS VALLEY. IN RESPONSE...LOW-LEVEL
MOISTURE WILL QUICKLY RETURN NWD TODAY ACROSS THE SABINE RIVER
VALLEY ADVECTING EWD INTO THE LOWER MS VALLEY TONIGHT. ALTHOUGH
MODEL FORECASTS DEVELOP THE GREATEST AMOUNT OF INSTABILITY OVER EAST
TX...A CAPPING INVERSION SHOULD KEEP THUNDERSTORMS FROM DEVELOPING
FOR MOST OF THE AFTERNOON INTO THE EARLY EVENING IN THE SRN PLAINS.
FURTHER EAST NORTHEAST ACROSS THE LOWER MS AND TN VALLEYS...THE GFS
AND NAM MODELS ARE IN AGREEMENT DEVELOPING A LARGE AREA OF
CONVECTION OVERNIGHT.
ALTHOUGH LARGE-SCALE ASCENT WILL NOT BE THAT STRONG ACROSS THE LOWER
MS AND TN VALLEYS...LIFT ASSOCIATED WITH THE LOW-LEVEL JET SHOULD
SUPPORT A LARGE AREA OF CONVECTION EXPANDING ENEWD WITH TIME
OVERNIGHT. A WARM FRONT IS FORECAST TO BE LOCATED ACROSS SW AR
EXTENDING SEWD ACROSS LA ALONG THE NERN GRADIENT OF THE LOW-LEVEL
MOIST AXIS. EAST NORTHEAST OF THE WARM FRONT...FORECAST SOUNDINGS
SUGGEST THE THUNDERSTORM ACTIVITY WILL BE ELEVATED IN NATURE WITH
PARCELS STARTING AT OR ABOUT 850 MB WITH MUCAPE VALUES GENERALLY
FROM 250 TO 750 J/KG. THIS WILL LIMIT THE WIND DAMAGE THREAT BUT
STRONG VERTICAL SHEAR PROFILES AND COLD TEMPS ALOFT /500 MB TEMPS OF
-14 TO -16C/ SHOULD BE SUFFICIENT FOR LARGE HAIL. THE LARGE HAIL
THREAT SHOULD EXPAND ENEWD WITH TIME AS CONVECTION EXPANDS IN
COVERAGE WITH THREAT REACHING MIDDLE TN AND NRN AL LATE IN THE
PERIOD.
CONCERNING THUNDERSTORM DEVELOPMENT FURTHER WEST SOUTHWEST TOWARD
CNTRL TX LATE THIS AFTERNOON...FORECAST SOUNDINGS SHOW A STOUT
CAPPING INVERSION IN PLACE. THIS ALONG WITH A LACK OF LARGE-SCALE
ASCENT SHOULD HAMPER UPDRAFT STRENGTH IN SPITE OF THE GREATER
INSTABILITY IN PLACE. FOR THIS REASON...IF THUNDERSTORMS CAN
INITIATE...ANY HAIL OR WIND DAMAGE THREAT SHOULD REMAIN MARGINAL
THROUGH EARLY EVENING. IN ERN TX...THERE EXISTS A POSSIBILITY FOR
SFC-BASED THUNDERSTORM DEVELOPMENT LATE IN THE PERIOD. FOR THIS
REASON...WILL MAINTAIN LOW PROBABILITIES FOR TORNADO AND WIND DAMAGE
IN THIS PART OF TX.
..BROYLES.. 02/17/2009
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