[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 200607
SWODY1
SPC AC 200606

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0106 AM CDT THU APR 20 2006

VALID 201200Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM TX ACROSS THE LOWER MS
VALLEY TO SRN KY...TN...WRN GA...

...SYNOPSIS...
SPRINGTIME CUTOFF LOW ACROSS THE UPPER MS VALLEY WILL MAKE ONLY SLOW
EWD PROGRESS TOWARD THE WRN GREAT LAKES THIS PERIOD AS A LOWER
AMPLITUDE AND MORE PROGRESSIVE IMPULSE IN THE SRN BRANCH MOVES EAST
FROM AZ/NM TO THE ARKLATEX. DOWNSTREAM FROM THE SRN BRANCH
IMPULSE...A MORE SUBTLE AND POTENTIALLY CONVECTIVELY ENHANCED SHORT
WAVE DISTURBANCE IS FORECAST TO TRACK EAST FROM THE SRN
PLAINS...ACROSS THE LOWER MS VALLEY...AND THEN TO THE CNTRL
APPALACHIANS THROUGH LATE TONIGHT. THE TWO SRN STREAM PERTURBATIONS
WILL ENHANCE ASCENT ALONG A QUASI-STATIONARY FRONTAL ZONE WHICH WILL
REMAIN SITUATED WITHIN A VERY WARM AND MOIST AIRMASS FROM TX TO TN.

...LOWER MS VALLEY/TN VALLEY...
ONGOING LARGE MCS FROM NRN TX TO AR WILL MOVE EWD FROM THE ARKLATEX
THROUGH THE MORNING SUSTAINED BY WEAK TO MODEST MOISTURE FLUX AND
ASCENT OCCURRING ACROSS STALLED DEEP-LAYER FRONTAL ZONE. GUIDANCE
APPEARS TO SUGGEST THAT A FRONTAL WAVE COINCIDENT WITH THIS COMPLEX
WILL PROPAGATE ENEWD ALONG THE FRONTAL BOUNDARY ACROSS THE LOWER MS
VALLEY AND INTO THE TN VALLEY THROUGH THE DAY WITH LARGE SCALE
ASCENT ACROSS THESE AREAS ENHANCED BY POSSIBLE MCV. RELATIVELY
UNDISTURBED WARM SECTOR AIR MASS SHOULD EXIST EAST OF THE
APPROACHING MCS...AND WEST OF RESIDUAL BACK DOOR FRONT/MCS
OUTFLOW...FROM MIDDLE TN TO NRN MS. EXPECT MODERATELY UNSTABLE
CONDITIONS TO DEVELOP ALONG THE FRONT IN THIS REGION THROUGH THE
MORNING GIVEN SUFFICIENT HEATING. FORCING ASSOCIATED WITH THE
APPROACHING WAVE SHOULD PROMOTE ADDITIONAL SURFACE-BASED TSTM
DEVELOPMENT FROM NRN MS/WRN TN...EWD ACROSS MIDDLE TN AND NRN AL
THROUGH THE AFTERNOON. FORECAST SOUNDINGS ACROSS THE REGION APPEAR
TO INDICATE WEAK EFFECTIVE SHEAR ACROSS THE WARM SECTOR INITIALLY
WHICH MAY RESULT IN GREATER CONCENTRATION OF MULTICELL STORMS WITH
SOME HAIL POTENTIAL. HOWEVER...MID LEVEL FLOW AND DEEP SHEAR
STRENGTHEN DURING THE AFTERNOON SO STORMS MAY BECOME BETTER
ORGANIZED ALONG THE FRONT AND NEAR SURFACE WAVE. THUS... EXPECT
ORGANIZED MULTICELLS AND PERHAPS A COUPLE OF SUPERCELLS SPREADING
EAST ACROSS THE REGION THROUGH THE AFTERNOON. THIS ACTIVITY WILL BE
CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WINDS. TORNADO
POTENTIAL MAY ALSO EVOLVE WITH CELLS TRACKING PREFERENTIALLY NEAR
THE FRONT...AND ACROSS THE RESIDUAL OUTFLOW BOUNDARY WHERE LOW LEVEL
FLOW WILL BE LOCALLY BACKED AND STRONGER SHEAR WILL LIKELY EXIST.

ANOTHER FOCUS FOR STORM DEVELOPMENT MAY EXIST FROM SRN GA WWD ACROSS
SRN AL AND MS BY LATE AFTERNOON. A SEGMENT OF RESIDUAL FRONT/OUTFLOW
MAY MOVE INTO THESE AREAS WHERE DIURNAL HEATING WILL BOOST CAPE BUT
REGION MAY REMAIN CAPPED UNTIL LATER IN THE DAY. MODEST MID LEVEL
FLOW WILL PROMOTE ORGANIZED STORMS DEVELOPING IN THIS REGIME WITH
ATTENDANT THREAT OF HAIL AND WIND. WITH DIURNAL FORCING BEING THE
PRIMARY FACTOR IN THE DEVELOPMENT OF THIS ACTIVITY...EXPECT SEVERE
POTENTIAL TO GRADUALLY WANE AFTER SUNSET.

...WEST TX TO THE ARKLATEX...
FRONTAL ZONE FROM HILL COUNTRY TO ARKLATEX WILL REMAIN WELL DEFINED
IN THE WAKE OF OVERNIGHT/MORNING MCS. AIR MASS ALONG AND SOUTH OF
THE FRONT IS EXPECTED TO BECOME INCREASINGLY UNSTABLE THROUGH THE
DAY WITH 60S DEWPOINTS AND STEEP MID LEVEL LAPSE RATES CONTRIBUTING
TO MLCAPE OF 1500-2000 J/KG. HEIGHT FALLS AND LARGE SCALE ASCENT
WITH APPROACHING SRN BRANCH SHORT WAVE TROUGH SHOULD INDUCE SURFACE
PRESSURE FALLS ACROSS WRN TX WITH WARM SECTOR POSSIBLY EXPANDING NWD
AS LOW LEVEL SELY FLOW STRENGTHENS AHEAD OF DEEPENING TRIPLE POINT
SURFACE WAVE AND SHARPENING DRYLINE.

FORECAST SOUNDINGS ACROSS THE REGION ARE INDICATING 40-45KT
EFFECTIVE SHEAR NEAR THE FRONT...AND DEVELOPING EWD ACROSS THE WARM
SECTOR INTO THE EVENING. GIVEN EXPECTED FORCING AND
INSTABILITY...ENVIRONMENT SHOULD SUPPORT THE DEVELOPMENT OF
SUPERCELLS CAPABLE OF PRODUCING LARGE...POSSIBLY SIGNIFICANT...
HAIL. ANY DISCRETE STORMS TRACKING NEAR/ALONG THE WSW-ESE ORIENTED
FRONTAL BOUNDARY...OR NEAR SURFACE WAVE...COULD ALSO POSE A THREAT
FOR TORNADOES WHERE LOW-LEVEL SHEAR AND BOUNDARY LAYER RH WILL BE
MAXIMIZED. STORMS MAY UNDERGO UPSCALE ORGANIZATION INTO AN MCS
THROUGH THE LATE EVENING AND DAMAGING WIND POTENTIAL MAY INCREASE AS
THIS MCS SPREADS EAST TOWARD THE GULF COAST THROUGH EARLY FRIDAY.

IT IS POSSIBLE THAT SEVERE WEATHER PROBABILITIES MAY BE
INCREASED...AND CATEGORICAL OUTLOOK COULD BE UPGRADED...ACROSS
PORTIONS OF TX AS EVOLUTION OF SEVERE WEATHER SCENARIO BECOMES MORE
CERTAIN WITH ADDITIONAL SHORT-TERM ANALYSIS AND FORECAST DATA.

..CARBIN/JEWELL.. 04/20/2006