SWODY1
SPC AC 031248
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0748 AM CDT THU APR 03 2008
VALID 031300Z - 041200Z
..THERE IS A MDT RISK OF SVR TSTMS LATE THIS AFTERNOON INTO TONIGHT
FOR N TX...S CENTRAL/SE OK...AND SW AR...
..THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK...FROM
SW TX TO THE WRN TN/KY AREA...
..SYNOPSIS...
A SRN STREAM TROUGH NOW OVER SRN CA IS LOSING AMPLITUDE WHILE
PROGRESSING EWD TOWARD THE BROAD CONFLUENCE OF THE NRN AND SRN
STREAMS. THE PRIMARY CA TROUGH IS PRECEDED BY A SERIES OF SPEED
MAXIMA FROM SRN AZ TO THE TX PANHANDLE. THESE LEAD SPEED MAXIMA
WILL CONTRIBUTE TO THE FORMATION OF A WEAK SURFACE WAVE ON THE WARM
FRONT THAT WILL DEVELOP ENEWD FROM NRN AR/SRN MO LATE THIS AFTERNOON
TO THE LOWER OH VALLEY TONIGHT. FARTHER W...A REMNANT LEE CYCLONE
IN SE CO WILL REFORM SEWD TOWARD NW TX IN ADVANCE OF THE CA MID
LEVEL TROUGH...AND THEN EWD ACROSS N/NE TX TONIGHT. AT THE SAME
TIME...THE SURFACE BAROCLINIC ZONE WILL BEGIN TO MOVE SEWD ACROSS
OK/NW TX IN THE WAKE OF THE LEAD WAVE.
A MOIST AIR MASS /BOUNDARY LAYER DEWPOINTS OF 65-70 F/ WILL SPREAD
NWD FROM TX/LA/MS TO OK/AR/TN THIS AFTERNOON. THIS MOISTENING WILL
OCCUR BENEATH A PLUME OF STEEP MID LEVEL LAPSE RATES...AND COMBINE
WITH DAYTIME HEATING TO SUPPORT STRONG WARM SECTOR INSTABILITY OVER
TX/OK. INSTABILITY IS MORE QUESTIONABLE ACROSS AR/TN AS A RESULT OF
RESIDUAL CLOUDS AND EARLY ELEVATED THUNDERSTORMS. MEANWHILE...THE
CORRIDOR OF STRONGER LOW-LEVEL FLOW IS FORECAST TO SHIFT NEWD TO
AR/MO EARLY IN THE DAY WITH THE LEAD WAVE...LEAVING WEAKER LOW-LEVEL
FLOW/SHEAR IN THE AREA OF STRONGEST INSTABILITY ACROSS N TX AND SRN
OK.
..AR/TN AREA TODAY INTO TONIGHT...
CURRENT EXPECTATIONS ARE FOR THUNDERSTORMS TO PERSIST THROUGH THE
DAY IN THE ZONE OF LOW-LEVEL WAA ACROSS AR/MO/TN/KY. ISOLATED LARGE
HAIL MAY OCCUR WITH THE ELEVATED CONVECTION THROUGH AT LEAST MIDDAY.
DURING THE AFTERNOON...LOW-LEVEL DESTABILIZATION MAY BECOME
SUFFICIENT FOR A FEW SURFACE-BASED STORMS ALONG THE SRN FRINGE OF
THE LARGER AREA OF CONVECTION...FROM CENTRAL AR INTO WRN TN OR
EXTREME NW MS. HERE...MODEST INSTABILITY AND SRH WITH A 40+ KT SWLY
LLJ WILL SUPPORT SOME THREAT FOR SUPERCELLS AND POTENTIALLY A COUPLE
OF TORNADOES...IN ADDITION TO LARGE HAIL AND DAMAGING WINDS. THE
PRIMARY UNCERTAINTIES WILL BE THE RATE OF LOW-LEVEL
DESTABILIZATION...AND THE DEGREE OF CONVECTIVE INHIBITION WITH THE
ELEVATED MIXED LAYER SAMPLED TO THE W/SW OF THIS AREA.
..OK/TX LATE THIS AFTERNOON AND OVERNIGHT...
THUNDERSTORM DEVELOPMENT ACROSS OK/N TX WILL LIKELY BE DELAYED UNTIL
LATE AFTERNOON/EVENING BY LINGERING CONVECTIVE INHIBITION WITH THE
ELEVATED MIXED LAYER...AND BY SLOW RECOVERY THIS AFTERNOON OF THE
LOW-LEVEL MASS FIELDS IN THE WAKE OF THE LEAD SHORTWAVE TROUGH.
FORECAST SOUNDINGS ACROSS SRN OK/N TX REVEAL MLCAPE VALUES AOA 2500
J/KG AND RELATIVELY STRONG DEEP LAYER SPEED SHEAR...BUT WEAK
LOW-LEVEL SHEAR THIS AFTERNOON. SUCH PROFILES WILL LIKELY FAVOR
SPLITTING SUPERCELLS CAPABLE OF PRODUCING VERY LARGE HAIL AND
DAMAGING WINDS. A FEW TORNADOES WILL BE POSSIBLE THIS EVENING WITH
THE MORE DISCRETE SUPERCELLS PRIMARILY E OF THE TRIPLE POINT AND S
OF THE COLD FRONT...IF THE LOW-LEVEL WINDS RETURN TO SLY AND SHEAR
INCREASES LIKE SHOWN IN THE 06Z NAM. SHORT TERM ASSESSMENT OF THE
TORNADO THREAT WILL REQUIRE CLOSE ATTENTION TO THE LOW-LEVEL WIND
FIELDS IN THIS COMPLICATED FLOW REGIME. LATER DURING THE EVENING
AND OVERNIGHT...CONVECTION WILL LIKELY EVOLVE INTO AN EXTENSIVE
ENE-WSW ORIENTED BAND ALONG THE COLD FRONT FROM N TX/SE OK ACROSS AR
TO WRN TN...WITH A CONTINUED THREAT FOR HAIL/DAMAGING WINDS AND VERY
HEAVY RAINFALL.
DESPITE A STRONG CAP IN 12Z SOUNDINGS...ISOLATED SUPERCELLS MAY FORM
LATE THIS AFTERNOON JUST W OF THE SJT-DRT CORRIDOR. STRONG SURFACE
HEATING/MIXING WILL REDUCE CONVECTIVE INHIBITION ALONG THE DRYLINE
AS THE BAND OF LEE MOUNTAIN CIRRUS CLEARS THIS AREA...RESULTING IN
STRONG INSTABILITY IN AN ENVIRONMENT WITH SUFFICIENT BULK SHEAR FOR
SUPERCELLS. A STORM OR TWO MAY ALSO FORM OVER THE HIGH TERRAIN W OF
DRT AND MOVE ACROSS THE RIO GRANDE BEFORE WEAKENING LATE THIS
EVENING.
.THOMPSON/GRAMS.. 04/03/2008
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