SWODY1
SPC AC 280101
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0801 PM CDT MON APR 27 2009
VALID 280100Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS SE TX/LOWER MS VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS PART OF SRN HIGH PLAINS...
...E/SE TX INTO SW LA...
GREATEST TORNADO AND DAMAGING WIND THREATS ARE EXPECTED TO RESIDE
ALONG LEADING EXTENT OF QUASI-LINEAR MCS...PRIMARILY FROM FAR SERN
TX/UPPER TX COAST INTO ADJACENT PART OF SW LA AS THIS SYSTEM
PROGRESSES ESEWD THIS EVENING. IMMEDIATE DOWNSTREAM AIR MASS AHEAD
OF THE MCS IS MODERATELY UNSTABLE AND EFFECTIVE BULK SHEAR AROUND 35
KT AND LOW LEVEL SRH /SFC-1 KM 200-300 M2/S2/ WILL MAINTAIN THESE
THREATS INTO THE MID EVENING. S OF THIS AREA ALONG THE MIDDLE TX
COAST...THE SEVERE WEATHER THREAT SHOULD BE FAIRLY LIMITED AS THIS
PORTION OF THE MCS WILL HAVE MOVED OFFSHORE BY 01Z. FOR ADDITIONAL
SEVERE AND HEAVY RAIN INFORMATION...REFER TO SPC MESOSCALE
DISCUSSION 610 FOR TORNADO WATCH 203.
LATER TONIGHT...MODELS ARE CONSISTENT SHOWING NEW TSTM DEVELOPMENT
ACROSS PARTS OF E TX IN THE WAKE OF THE CURRENT MCS...NOW
APPROACHING THE MIDDLE/UPPER TX COAST. LAPSE RATES WILL BE WEAK
OVER THIS REGION...BUT STRENGTHENING SLY LLJ ACROSS S AND SE TX WILL
RESULT IN MOISTURE RETURN/WAA INTO E TX OVERNIGHT AND SUPPORT AT
LEAST WEAK DESTABILIZATION. THE POTENTIAL FOR ORGANIZED STORMS
SHOULD BE LOW GIVEN GENERALLY WEAK WLY MID LEVEL WINDS EXPECTED
ACROSS E TX LATER TONIGHT. NONETHELESS...MUCAPE 500-1000 J/KG AND
LOW LEVEL SHEAR ENHANCED ALONG SLY LLJ MAY PROVE SUFFICIENT FOR AN
ISOLATED SEVERE THREAT...AND THUS WILL OUTLOOK LOW SEVERE
PROBABILITIES FOR THIS REGION.
...W TX...
WATER VAPOR IMAGERY INDICATED A MID LEVEL IMPULSE...CURRENTLY
TRACKING EWD ACROSS AZ/NWRN MEXICO. THIS FEATURE AND ACCOMPANYING
50 KT WSWLY MID LEVEL JET ARE EXPECTED TO REACH NM/NRN CHIHUAHUA BY
12Z. SELY LLJ ACROSS W TX/FAR ERN NM IS EXPECTED TO STRENGTHEN TO
25-30 KT TONIGHT RESULTING IN INCREASING LOW LEVEL WAA N OF SURFACE
FRONT WHICH SHOULD EXTEND FROM NRN TX WSWWD INTO WEST CENTRAL TX BY
12Z. STEEP MID LEVEL LAPSE RATES /7-8 C/KM/ SPREADING EWD WITH SRN
STREAM TROUGH COMBINED WITH LOW LEVEL MOISTURE/WARM AIR ADVECTION
ALONG LLJ WILL AID IN DESTABILIZATION WITH MUCAPE RANGING FROM
500-1000 J/KG AFTER 06Z. THIS COMBINED WITH INCREASING EFFECTIVE
BULK SHEAR ARE EXPECTED TO SUPPORT A HAIL THREAT WITH ANY STORMS
THAT FORM FROM MAINLY THE TX PANHANDLE INTO FAR NERN NM AND ADJACENT
OK PANHANDLE.
...LOWER/MID MS AND LOWER OH VALLEYS...
A SHORT WAVE TROUGH WILL TRACK NEWD FROM E TX INTO THE LOWER OH
VALLEY TONIGHT. ASCENT AHEAD OF THIS FEATURE COMBINED WITH LOW
LEVEL CONVERGENCE ALONG A COLD FRONT MOVING EWD INTO THIS REGION AND
ALONG PRE-FRONTAL CONVERGENCE ZONES WILL SUPPORT ADDITIONAL
SHOWERS/EMBEDDED TSTM DEVELOPMENT ACROSS THIS REGION OVERNIGHT.
A CONTINUED GRADUAL DIMINISHING TREND IN THE SEVERE WEATHER THREAT
IS EXPECTED ALONG THE LOWER-MID MS VALLEY AS THE LOSS OF SURFACE
HEATING AND GENERALLY WEAK LAPSE RATES RESULT IN WEAK INSTABILITY.
SSWLY LLJ IS EXPECTED TO STRENGTHEN /30-40 KT/ THIS FORECAST PERIOD
FROM ERN AR INTO LOWER OH VALLEY. THIS MAY PROMOTE A FEW STRONGER
WIND GUSTS.
..PETERS.. 04/28/2009
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