Feb 18, 2009 1300 UTC Day 1 Convective Outlook
Updated: Wed Feb 18 13:00:20 UTC 2009
Probabilistic to Categorical Outlook Conversion Table (Effective Feb 14, 2006).
Categorical Graphic
20090218 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20090218 1300 UTC Day 1 Tornado Probabilities Graphic
Torndao Legend Image
Probabilistic Damaging Wind Graphic
20090218 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Wind Legend Image
Probabilistic Large Hail Graphic
20090218 1300 UTC Day 1 Large Hail Probabilities Graphic
Hail Legend Image
   SPC AC 181256
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0656 AM CST WED FEB 18 2009
   
   VALID 181300Z - 191200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF LA...MS...AL...GA
   AND THE FL PANHANDLE...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA
   FROM LA INTO PARTS OF TN...GA...NRN FL AND THE S ATLANTIC CST...
   
   ...SYNOPSIS...
   FAST WSW FLOW WILL PREVAIL OVER THE S CNTRL AND SE U.S. TODAY/
   TONIGHT...ON SRN FRINGE OF NRN STREAM TROUGH AMPLIFYING SE ACROSS
   THE UPR GRT LKS/MID MS VLY.  S OF THE TROUGH...EXISTING SRN BRANCH
   JET...NOW EXTENDING FROM NM TO AR...WILL DEVELOP ESEWD.  THIS WILL
   ENHANCE MID LVL FLOW OVER THE SERN STATES TODAY...WITH MORE
   SUBSTANTIAL STRENGTHENING EXPECTED TONIGHT/EARLY THURSDAY.
   
   AT THE SFC...LOW ASSOCIATED WITH NRN STREAM IMPULSE SHOULD TRACK NE
   TO NEAR LK HURON THIS EVE AS TRAILING COLD FRONT CONSOLIDATES AND
   ACCELERATES SE ACROSS THE OH...TN...AND LWR MS VLYS.  AHEAD OF THE
   FRONT...LATEST HAND AND STREAMLINE ANALYSES SUGGEST PRESENCE OF A
   CONFLUENCE ZONE ATTM EXTENDING FROM NEAR MEM SW TO NEAR SHV. 
   SATELLITE PW AND VWP DATA SUGGEST THAT THIS FEATURE MAY MARK WRN
   LIMIT OF POTENTIAL STORM DEVELOPMENT TODAY AS WINDS APPEARED TO HAVE
   VEERED BEHIND IT...AND DRYING IS OCCURRING TO ITS W.
   
   ...TN VLY TO CNTRL GULF CST/GA/N FL...
   POTENTIAL EXISTS FOR SIGNIFICANT SVR STORMS THIS AFTN THROUGH EARLY
   THURSDAY AHEAD OF AFOREMENTIONED COLD FRONT AND CONFLUENCE ZONE.
   
   LATEST SATELLITE PW DISPLAY SHOWS PW AXIS WITH VALUES AOA 1 INCH
   EXTENDING FROM SE TX AND LA NE INTO MIDDLE TN.  THIS MOISTURE AXIS
   SHOULD CONTINUE TO PIVOT CLOCKWISE ACROSS THE CNTRL GULF CST STATES
   TODAY AS HEIGHTS SLOWLY FALL OVER REGION ON SRN FRINGE OF AMPLIFYING
   TROUGH.  
   
   ALTHOUGH THE INCREASING MOISTURE WILL ENHANCE LIKELIHOOD FOR
   STORMS...SEVERAL FACTORS ARGUE AGAINST MORE THAN ISOLD ACTIVITY IN
   THE SLGT AND MDT RISK AREAS UNTIL PERHAPS LATE THIS AFTN AND THIS
   EVE.  FIRST /1/ MORNING RAOBS AND MODEL FCSTS SHOW THAT MID LVL
   LAPSE RATES ARE AND LIKELY WILL REMAIN ONLY MODESTLY STEEP...WITH A
   WARM NOSE AROUND 750 MB.  IN ADDITION.../2/ CLOUDS WITH S-DRIFTING
   SUBTROPICAL JET WILL LIMIT SFC HEATING THROUGH AT LEAST PART OF THE
   DAY NEAR THE GULF CST.  THIRD /3/ DEEP FORCING FOR ASCENT WILL BE
   WEAK AS UPLIFT LIKELY WILL BE CONCENTRATED ON CYCLONIC SIDE OF SRN
   STREAM JET...I.E. OVER THE OH VLY/CNTRL APPALACHIANS.
   
   NEVERTHELESS...COMBINATION OF SFC HEATING...ESPECIALLY IN THE TN
   VLY...WITH PERSISTENT LOW LVL CONFLUENCE SHOULD BE SUFFICIENT TO
   OVERCOME NEGATIVE FACTORS AND SUPPORT AT LEAST WIDELY SCTD STORMS
   ALONG CONFLUENCE ZONE OVER PARTS OF LA...MS AND AL.  A SEPARATE AREA
   OF ISOLD TO WDLY SCTD STORMS ALSO MAY FORM ALONG COLD FRONT IN
   TN/KY.
   
   GIVEN INTENSITY AND EXPECTED INCREASE IN DEEP WSWLY FLOW /SPEEDS AOA
   70 KTS AT 500 MB/...EXPECT ANY SUSTAINED UPDRAFTS THAT DO FORM WILL
   QUICKLY BECOME SVR SUPERCELLS.  DESPITE LARGELY UNIDIRECTIONAL
   FLOW...LENGTH OF HODOGRAPHS /60-70 KT 0-6 KM SHEAR/ COULD YIELD
   ISOLD STRONG TORNADOES...IN ADDITION TO BOWING SEGMENTS WITH HIGH
   WIND.
   
   ALTHOUGH THE STORMS ALONG THE COLD FRONT SHOULD DIMINISH UPON
   ENCOUNTERING LESS FAVORABLE LOW LVL THERMODYNAMIC ENVIRONMENT IN THE
   SRN/CNTRL APPALACHIANS...THOSE THAT FORM ALONG PRE-FRONTAL
   CONFLUENCE BAND COULD STRENGTHEN THROUGH THE EVE AS /1/ MORE
   SUBSTANTIAL HEIGHT FALLS OVERSPREAD REGION AND /2/ LOW LVL MOISTURE
   INFLOW CONTINUES TO INCREASE ALONG THE CNTRL/ERN GULF CST.  SOME OF
   THE STORMS COULD MOVE/DEVELOP E ACROSS CNTRL/SRN GA AND N FL GIVEN
   DEEP UNIDIRECTIONAL FLOW.
   
   ..CORFIDI.. 02/18/2009
   
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