DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 180102
SWODY1
SPC AC 180059

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0659 PM CST TUE FEB 17 2009

VALID 180100Z - 181200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF SRN AR...FAR NE
TX...NRN LA...NRN MS...WRN TN AND FAR NW AL...

...OZARKS/LOWER MS AND TN VALLEYS...
AT 01Z...WATER VAPOR IMAGERY SHOWS A WEST SOUTHWEST FLOW PATTERN IN
PLACE ACROSS THE SRN STATES WITH THE SUBTROPICAL PLUME EXTENDING
ENEWD ACROSS NRN MEXICO INTO TX AND THE LOWER MS VALLEY. A 45 TO 55
KT LOW-LEVEL JET IS ANALYZED OVER ERN OK AND AR WITH THE SRN EXTENT
OF THE JET IN ERN TX. IN RESPONSE TO THE LOW-LEVEL JET...MOISTURE
ADVECTION IS OCCURRING ACROSS EAST TX WHERE SFC DEWPOINTS ARE NOW
APPROACHING 60 F. THUNDERSTORMS ARE DEVELOPING DUE TO LIFT
ASSOCIATED WITH THE LOW-LEVEL JET ON THE LEADING EDGE OF THE
MOISTURE RETURN. MODEL FORECASTS ARE IN GENERAL AGREEMENT EXPANDING
THIS ACTIVITY ENEWD WITH THE POSITION OF THE LOW-LEVEL JET ACROSS
AR...NRN LA INTO NRN MS AND WRN TN DURING THE OVERNIGHT PERIOD.

CONCERNING THE NATURE OF THE CONVECTION...RUC FORECAST SOUNDINGS
ACROSS THE ARKLATEX THIS EVENING SUGGEST THE ACTIVITY IS ELEVATED
WITH PARCELS STARTING AT ABOUT 850 MB. AT MID-LEVELS...A 500 MB TEMP
TROUGH IS ANALYZED OVER THE ARKLATEX WITH 500 MB TEMPS AROUND -14C.
THIS ALONG WITH 850 TO 500 MB LAPSE RATES OF 6.5 TO 7.0 C/KM SHOULD
SUPPORT A HAIL THREAT. AS THIS COLD AIR ALOFT ADVECTS EWD AND
MOISTURE INCREASES WITH THE LOW-LEVEL JET...THE HAIL THREAT SHOULD
GRADUALLY EXPAND ACROSS ERN AR...NRN MS INTO WRN TN. IN ADDITION...A
FEW AREAS COULD RECEIVE LARGE HAIL DUE TO THE STRONG VERTICAL SHEAR
WHICH COULD SUPPORT AN ISOLATED SUPERCELL THREAT.

FURTHER WEST SOUTHWEST...MODEL FORECASTS REDEVELOP CONVECTION LATE
TONIGHT FROM THE ARKLATEX EWD ACROSS SRN AR ALONG THE MOIST AXIS. BY
THIS TIME...FORECAST SOUNDING SHOW MUCAPE VALUES AROUND 1000 J/KG
WITH SFC PARCELS STARTING IN THE BOUNDARY LAYER. THIS COULD BE
SUFFICIENT FOR SFC-BASED STORMS WITH A CONTINUING A SEVERE THREAT
LATE IN THE PERIOD. HAIL AND MARGINALLY SEVERE WIND DAMAGE WOULD BE
THE PRIMARY THREATS WITH THE ACTIVITY.

..BROYLES.. 02/18/2009

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