[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 200545
SWODY1
SPC AC 200543

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1143 PM CST MON FEB 19 2007

VALID 201200Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT OVER
PORTIONS OF THE MID SOUTH...

...SYNOPSIS...

SRN BRANCH...POSITIVELY TILTED UPPER TROUGH /CURRENTLY FROM THE FOUR
CORNERS REGION INTO THE LOWER CO VALLEY/ IS FORECAST TO BECOME
INCREASINGLY SHEARED AS IT PROGRESSES EWD THROUGH THE SRN PLAINS
INTO LOWER MS VALLEY THIS PERIOD.  ACCOMPANYING SUBTROPICAL MID AND
UPPER LEVEL JET STREAKS WILL CONCURRENTLY PROPAGATE EWD THROUGH THE
S-CNTRL AND SERN STATES IN ADVANCE OF INTENSIFYING UPSTREAM TROUGH
OVER THE NERN PACIFIC.

IN THE LOW-LEVELS...SURFACE LOW ATTENDANT TO SRN STREAM SHORT WAVE
TROUGH WILL DEVELOP GENERALLY EWD FROM NERN OK TO JUST W OF MEM BY
21/00Z...PRIOR TO WEAKENING WHILE MOVING THROUGH THE SRN
APPALACHIANS LATE TONIGHT.  ASSOCIATED COLD FRONT WILL PUSH SLOWLY
SEWD...AND WILL EXTEND FROM ALONG THE OH RIVER SWWD TO SURFACE LOW
NEAR MEM TO THE ARKLATEX THIS EVENING.  THIS SURFACE LOW AND FRONT
WILL BE THE PRIMARY FOCUS FOR TSTM DEVELOPMENT /SOME POTENTIALLY
SEVERE/ FROM LATE THIS AFTERNOON INTO TONIGHT.

...MID SOUTH...

20/00Z SOUNDINGS FROM THE WRN GULF COAST AND CURRENT GOES SOUNDER PW
LOOP INDICATE A MODIFIED CP AIR MASS /CHARACTERIZED BY MID TO UPPER
50S DEWPOINTS/ RETURNING NNEWD THROUGH E TX AND WRN LA. 
STRENGTHENING SWLY SURFACE WINDS WILL SUPPORT A CONTINUED NEWD
ADVECTION OF THIS AIR MASS INTO REGION AHEAD OF SURFACE LOW AND COLD
FRONT.  HOWEVER...LARGELY ZONAL AIR STREAM IN THE 850-700 MB LAYER
WILL RESULT IN THE EWD ADVECTION OF SRN HIGH PLAINS ELEVATED MIXED
LAYER...EFFECTIVELY CAPPING SHALLOW...MOISTENING BOUNDARY LAYER. 
MOREOVER...CONSIDERABLE MID AND HIGH LEVEL CLOUDINESS EMBEDDED
WITHIN SUBTROPICAL JET WILL LIKELY LIMIT DIABATIC HEATING ACROSS
MUCH OF WARM SECTOR AIR MASS...WITH STRONGEST DESTABILIZATION
EXPECTED IN A RELATIVELY NARROW ZONE AHEAD OF FRONT OVER NRN/CNTRL
AR INTO WRN TN/NRN MS.

THE ABOVE FACTORS SUGGEST THAT ANY DEEP CONVECTIVE DEVELOPMENT WILL
BE CLOSELY TIED TO STRONGER SYNOPTIC AND MESOSCALE FORCING
ASSOCIATED WITH APPROACHING UPPER TROUGH AND SURFACE FRONT. 
INDEED...LATEST SHORT TERM MODEL GUIDANCE INDICATES THAT TSTMS WILL
BECOME INCREASINGLY LIKELY LATE THIS AFTERNOON OR EARLY EVENING
INVOF SURFACE LOW OVER NERN AR/MO BOOTHEEL/WRN TN WHERE LOW-LEVEL
CONVERGENCE WILL BE MAXIMIZED.  GIVEN THE ANTICIPATED MODEST
INSTABILITY /MLCAPES OF 500-700 J PER KG/...RELATIVELY STRONG DEEP
LAYER SPEED SHEAR WITHIN THIS INITIATION ZONE SHOULD SUPPORT
ORGANIZED/ROTATING STORMS CAPABLE OF PRIMARILY DAMAGING WINDS AND
LARGE HAIL.  A TORNADO OR TWO IS POSSIBLE WITH ANY STORMS THAT CAN
REMAIN DISCRETE...NAMELY OVER WRN TN...WHERE LOW LEVEL SHEAR IS
FORECAST TO REMAIN RELATIVELY STRONG THROUGH THE EVENING HOURS.

ACTIVITY SHOULD QUICKLY EVOLVE INTO ONE OR MORE LARGER CLUSTERS WITH
A MARGINAL WIND/HAIL THREAT DEVELOPING ESEWD THROUGH THE TN VALLEY
AND NRN PORTIONS OF MS/AL.

..MEAD.. 02/20/2007