SWODY3
SPC AC 230722
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0222 AM CDT MON MAR 23 2009
VALID 251200Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF CNTRL TX EWD
INTO PARTS OF THE LOWER MS VALLEY...
...SYNOPSIS...
A BROADLY-CYCLONIC LARGE-SCALE PATTERN WILL EXIST OVER MUCH OF THE
CONUS THROUGH THE DAY THREE PERIOD. THE PRIMARY FEATURE OF INTEREST
APPEARS TO BE A VORTICITY MAXIMUM WHICH WILL TRANSLATE FROM THE SRN
ROCKIES EWD INTO THE GULF COAST STATES. LATEST MODEL GUIDANCE
INDICATES DIFFERENCES IN BOTH THE INTENSITY AND THE RATE OF EWD
PROGRESSION OF THIS FEATURE. THE NAM IS THE OUTLIER...SUGGESTING A
MORE INTENSE AND SLOWER-MOVING SHORT WAVE TROUGH THAN THE
GFS...ECMWF AND MAJORITY OF SREF MEMBERS. WHILE BOTH THE GFS AND
ECMWF HAVE TRENDED TO A SLIGHTLY STRONGER SHORT WAVE TROUGH...THEY
STILL REMAIN MUCH MORE PROGRESSIVE THAN THE NAM.
AT THE SURFACE...COLD FRONT ASSOCIATED WITH A LEAD SHORT WAVE TROUGH
LIFTING NEWD THROUGH THE LOWER GREAT LAKES WILL PROGRESS EWD THROUGH
THE OH VALLEY. THE SRN EXTENSION OF THIS BOUNDARY WILL EVENTUALLY
STALL /IN A MORE W-E ORIENTATION/ ACROSS THE GULF COAST STATES INTO
TX BEFORE LIFTING NWD DURING THE LATTER HALF OF THE PERIOD WITH
APPROACH OF SRN ROCKIES IMPULSE. HERE TOO...DIFFERENCES EXIST EVEN
BETWEEN THE GFS AND ECMWF WITH THE LATTER DEVELOPING A SURFACE WAVE
ON THE BOUNDARY OVER THE LOWER MS VALLEY WEDNESDAY NIGHT.
...SRN PLAINS TO CNTRL GULF STATES...
CLUSTERS OF TSTMS ARE EXPECTED TO PERSIST THROUGH THE DAY ALONG AND
S OF STALLING FRONTAL ZONE OVER SRN PARTS OF AL/MS/LA. MIDLEVEL
LAPSE RATES WILL REMAIN WEAK...BUT THE COMBINATION OF 60+ F
DEWPOINTS AND DAYTIME HEATING WILL CONTRIBUTE TO POCKETS OF MODERATE
INSTABILITY. LOW-LEVEL WIND FIELDS WILL REMAIN RATHER WEAK THROUGH
THE DIURNAL HEATING CYCLE...THOUGH THE PRESENCE OF STRENGTHENING MID
AND HIGH-LEVEL FLOW WILL RESULT IN SUFFICIENT VERTICAL SHEAR FOR A
FEW STRONG/MARGINALLY SEVERE STORMS.
UPSTREAM OVER THE SRN PLAINS...AN EML WILL BE RENEWED IN ADVANCE OF
MIDLEVEL SYSTEM MOVING OUT OF THE SRN ROCKIES. THESE STEEP MIDLEVEL
LAPSE RATES WILL COINCIDE WITH RAPIDLY RETURNING LOW-LEVEL MOISTURE
THROUGH THE LOWER RIO GRANDE VALLEY AND CNTRL TX WITH AIR MASS
BECOMING MODERATELY UNSTABLE TO THE S OF RETREATING WARM FRONT.
INCREASED FORCING /DCVA/ ASSOCIATED WITH APPROACHING SHORT WAVE
TROUGH COUPLED WITH STRENGTHENING LOW-LEVEL WAA ARE EXPECTED TO
CONTRIBUTE TO SURFACE-BASED TSTM DEVELOPMENT BY AFTERNOON FROM
VICINITY OF DRYLINE EWD ALONG RETREATING WARM FRONT. ELEVATED TSTMS
WILL ALSO BECOME MORE WIDESPREAD WEDNESDAY AFTERNOON INTO WEDNESDAY
NIGHT NWD THROUGH THE RED RIVER VALLEY. VERTICAL SHEAR WILL BE
QUITE SUFFICIENT FOR SUPERCELLS IN BOTH THE SURFACE-BASED AND
ELEVATED STORM REGIMES.
TSTMS /SOME SEVERE/ WILL LIKELY SPREAD EWD INTO THE LOWER MS VALLEY
OVERNIGHT ALONG STRENGTHENING...NOCTURNAL LLJ. SHOULD THE ECMWF
SOLUTION VERIFY /I.E. STRONGER SURFACE WAVE/...POTENTIAL WILL EXIST
FOR SUPERCELLS AND TORNADOES ALONG SURFACE LOW TRACK WHERE STRONG
LOW-LEVEL SHEAR WILL BE COLLOCATED WITH MOIST BOUNDARY LAYER
CONDITIONS.
..MEAD.. 03/23/2009
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