From SPC…
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1139 AM CDT THU APR 02 2009
VALID 021630Z – 031200Z
…THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON INTO EARLY
TONIGHT FOR CENTRAL/NRN MS AND AL…
…THERE IS A MDT RISK OF SVR TSTMS THROUGH EARLY TONIGHT FOR N FL
AND S GA…
…THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK
AREAS…FOR THE LOWER MS/OH VALLEYS INTO THE SE ATLANTIC COASTAL
PLAIN…
…SYNOPSIS…
COMPLICATED SCENARIO TODAY WITH THE LARGE ONGOING MCS ACROSS THE NE
GULF COAST…AND PRE-FRONTAL CONVECTION SURGING EWD FROM LA/AR
TOWARD MS AS OF MID-LATE MORNING. THESE CONVECTIVE SYSTEMS WILL
HAVE A POTENTIALLY LARGE IMPACT ON THE SEVERE WEATHER THREAT TODAY
INTO AT LEAST EARLY TONIGHT.
…MCS FROM NE GULF COAST TO S GA THROUGH EARLY TONIGHT…
THE TRAINING CONVECTION WITHIN THE GULF COAST MCS WILL LIKELY
PERSIST THROUGH THE AFTERNOON WHILE SPREADING ENEWD ACROSS N FL/S
GA/SRN SC. THIS CONVECTION WILL BE SUSTAINED BY A CONTINUED INFLUX
OF 68-70 F BOUNDARY LAYER DEWPOINTS FROM THE NE GULF OF MEXICO…AND
IN THE ZONE OF LOW-LEVEL WAA AND UPPER DIVERGENCE ASSOCIATED WITH A
SPEED MAX EMBEDDED WITHIN THE SUBTROPICAL JET. A GRADUAL INCREASE
IN THE MAGNITUDE OF THE LLJ AND RESULTANT LOW-LEVEL SHEAR WILL
RESULT IN AN INCREASE IN THE THREAT FOR EMBEDDED SUPERCELLS WITH
TORNADOES IN THE LARGER CONVECTIVE SYSTEM THIS AFTERNOON INTO EARLY
TONIGHT.
…PRE-FRONTAL CONVECTION TODAY ACROSS LA/MS/AL/TN…
THE PRE-FRONTAL CONVECTION CROSSING THE MS RIVER /WITH AN
ACCOMPANYING COLD POOL AND POSSIBLE GRAVITY WAVE/ WILL LIKELY SWEEP
EWD ACROSS MUCH OF MS BY EARLY AFTERNOON AND INTO AL. 15Z SOUNDINGS
FROM JAN/LIX HAVE SHOWN SOME LOW-LEVEL DRYING SINCE 12Z…BUT STEEP
MID LEVEL LAPSE RATES WILL STILL SUPPORT MODERATE-STRONG INSTABILITY
/MLCAPE OF 1500-2000 J/KG/ WITH DAYTIME HEATING. VERTICAL SHEAR
WILL BE SUFFICIENT FOR SUPERCELLS WITHIN THE PRE-FRONTAL CONVECTIVE
BAND…WHILE LOW-LEVEL SHEAR/MOISTURE APPEAR TO BE LARGE ENOUGH TO
SUPPORT A FEW TORNADOES. FARTHER E…THE DISTRIBUTION OF LOW-LEVEL
MOISTURE/SURFACE HEATING AND RESULTANT INSTABILITY IS IN QUESTION
ACROSS AL GIVEN THE RELATIVELY EARLY ARRIVAL OF THE PRE-FRONTAL
LINE…AND THE ONGOING CONVECTION WITH RAIN-COOLED AIR ACROSS SE AL.
STILL…THE PRESENCE OF BOUNDARY LAYER DEWPOINTS IN THE 60S AND AT
LEAST WEAK INSTABILITY WILL SUPPORT SOME THREAT FOR SUPERCELLS/BOW
ECHOES WITH THE PRE-FRONTAL CONVECTION THIS AFTERNOON.
…SYNOPTIC LOW ACROSS AR/TN/NRN MS AND AL LATE EVENING…
THE PRE-FRONTAL CONVECTION WILL REDUCE INSTABILITY THROUGH THE
MAJORITY OF THE INLAND WARM SECTOR ACROSS THE LOWER MS VALLEY BY
MID-LATE AFTERNOON. THIS WILL LEAVE A NARROW BELT OF SURFACE
HEATING AND RESIDUAL MOISTURE ACROSS THE ARKLAMISS REGION LATER THIS
AFTERNOON…ALONG THE SYNOPTIC COLD FRONT AND NEAR THE CYCLONE
CENTER /WHICH IS NOW JUST W OF TXK/. THIS REGION OF STRONG FORCING
WILL THEN SPREAD EWD OVER NRN MS/TN/NRN AL THROUGH THE EVENING/EARLY
TONIGHT. THE MOST FAVORABLE WIND PROFILES FOR TORNADIC SUPERCELLS
ARE EXPECTED IMMEDIATELY E/SE OF THE SURFACE LOW ACROSS THE MDT RISK
AREA IN MS/AL…WHERE AN ISOLATED STRONG TORNADO OR TWO COULD STILL
OCCUR LATER THIS EVENING. THE PRIMARY UNCERTAINTY ACROSS NRN MS/WRN
AND MIDDLE TN/NRN AL WILL BE THE DEGREE OF RECOVERY/ DESTABILIZATION
IN THE WAKE OF THE AFTERNOON STORMS.
..THOMPSON/GRAMS.. 04/02/2009
