Feb 18, 2009 2000 UTC Day 1 Convective Outlook
Updated: Wed Feb 18 19:44:22 UTC 2009
Probabilistic to Categorical Outlook Conversion Table (Effective Feb 14, 2006).
Public Severe Weather Outlook

The SPC is forecasting ...significant severe thunderstorms expected over parts of the gulf coast states this afternoon and tonight....   Please read the latest public statement about this event.

Categorical Graphic
20090218 2000 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20090218 2000 UTC Day 1 Tornado Probabilities Graphic
Torndao Legend Image
Probabilistic Damaging Wind Graphic
20090218 2000 UTC Day 1 Damaging Wind Probabilities Graphic
Wind Legend Image
Probabilistic Large Hail Graphic
20090218 2000 UTC Day 1 Large Hail Probabilities Graphic
Hail Legend Image
   SPC AC 181940
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0140 PM CST WED FEB 18 2009
   
   VALID 182000Z - 191200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS LATE THIS AFTN ACROSS PARTS OF E
   CNTRL MS...NRN AND CNTRL AL INTO NRN/WRN GA....
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF THE CNTRL/ERN
   GULF STATES INTO PARTS OF THE OH VALLEY....
   
   DRY LINE STRUCTURE...NEAR THE INTERFACE OF THE PRE-FRONTAL THERMAL
   RIDGE AXIS AND THE WESTERN GRADIENT OF LOW-LEVEL MOISTURE RETURN OFF
   THE GULF OF MEXICO...APPEARS LIKELY TO REMAIN THE PRIMARY FOCUS FOR
   VIGOROUS CONVECTIVE DEVELOPMENT THROUGH THE REMAINDER OF THE
   AFTERNOON.  THIS CURRENTLY EXTENDS FROM THE LOWER MISSISSIPPI VALLEY
   INTO THE LOWER OHIO VALLEY...BUT IS SHIFTING EAST
   SOUTHEASTWARD...AND WILL BE OVERTAKEN BY THE COLD FRONT ACROSS
   KENTUCKY...MUCH OF TENNESSEE AND NORTHERN MISSISSIPPI DURING THE
   NEXT FEW HOURS.
   
   ...KENTUCKY/TENNESSEE INTO MID ATLANTIC STATES...
   AS THE EXIT REGION OF A 90-100 KT 500 MB JET STREAK SPREADS
   NORTHEAST OF REGION...INTO THE UPPER OHIO VALLEY...IT IS UNCLEAR IF
   ACTIVITY WILL EVOLVE INTO A MORE CONSOLIDATED FRONTAL LINE...OR
   REMAIN IN THE FORM OF BROKEN LINES OR DISCRETE SUPERCELLS.  BUT... A
   SEVERE THREAT IS EXPECTED TO PERSIST UNTIL LAPSE RATES STABILIZE AS
   THE NOSE OF THE PRE-FRONTAL THERMAL RIDGE BECOMES SUPPRESSED
   SOUTHWARD INTO THE NORTHERN GULF STATES LATER THIS AFTERNOON. 
   VIGOROUS CONVECTIVE ACTIVITY MAY ATTEMPT TO SPREAD EASTWARD AHEAD OF
   THE AMPLIFYING UPPER TROUGH AXIS...ACROSS THE CENTRAL APPALACHIANS. 
   HOWEVER...THIS WILL BECOME FURTHER REMOVED FROM AN INCREASINGLY
   PINCHED OFF LOW-LEVEL INSTABILITY AXIS TO THE WEST OF THE
   APPALACHIANS...AND THE SEVERE THREAT IS EXPECTED TO BECOME
   PROGRESSIVELY DIMINISHED WITH EASTWARD EXTENT.
   
   ...LWR MISSISSIPPI VALLEY INTO THE SOUTH ATLANTIC COAST STATES...
   HIGH RESOLUTION MODELS SUGGEST POTENTIAL FOR AN EVOLVING CONVECTIVE
   CLUSTER IS NOT PARTICULARLY HIGH.  BUT...THE BEST CHANCE FOR MORE
   ORGANIZED CONVECTIVE DEVELOPMENT...IF IT WERE TO OCCUR...APPEARS TO
   BE IN ASSOCIATION WITH STRONGER MID-LEVEL FORCING NEAR THE BASE OF
   THE AMPLIFYING UPPER TROUGH.  THIS IS EXPECTED TO GRADUALLY
   DEVELOP/STRENGTHEN ACROSS NORTHERN ALABAMA INTO NORTHERN/CENTRAL
   GEORGIA LATE THIS AFTERNOON AND EVENING... BEFORE SPREADING
   SOUTHEASTWARD TOWARD THE SOUTH ATLANTIC COAST TONIGHT.  SCATTERED
   STORM DEVELOPMENT IS ALREADY UNDERWAY ACROSS PARTS OF
   NORTHERN/CENTRAL ALABAMA...WHERE DEEP LAYER SHEAR IS STRONG AND
   LOW-LEVEL HODOGRAPHS STILL SIZABLE...SUPPORTING AT LEAST THE RISK
   FOR A COUPLE OF SUPERCELLS WITH THE POTENTIAL FOR TORNADOES LATE
   THIS AFTERNOON AND EARLY EVENING.
   
   OTHERWISE...BREAKS IN CLOUD COVER ARE ALLOWING FOR INCREASED
   INSOLATION WITHIN A MOISTENING BOUNDARY LAYER EAST OF THE LOWER
   MISSISSIPPI VALLEY THROUGH MUCH OF CENTRAL/SOUTHERN GEORGIA.  AS DEW
   POINTS CLIMB...MIXED LAYER CAPE OF 500-1000 J/KG WILL BECOME MORE
   PREVALENT LATE THIS AFTERNOON.  THIS WILL SUPPORT INTENSIFICATION OF
   CONVECTION ALONG THE PRE-FRONTAL MOISTURE GRADIENT...WITH PERHAPS
   ADDITIONAL STORMS DEVELOPING TO THE EAST.
   DUE TO LINGERING MID-LEVEL INHIBITION...AND THE WEAK TO MODEST
   NATURE OF THE MID/UPPER FORCING...STORMS PROBABLY WILL REMAIN
   DISCRETE AND SOMEWHAT WIDELY SCATTERED.  IN THE PRESENCE OF STRONG
   DEEP LAYER SHEAR...A FEW SUPERCELLS ARE LIKELY.  DESPITE A TENDENCY
   FOR SHRINKING LOW-LEVEL HODOGRAPHS DUE TO WEAKENING AND VEERING
   LOW-LEVEL WIND FIELDS...ENVIRONMENT MAY STILL SUPPORT THE RISK FOR
   ISOLATED TORNADOES...IN ADDITION TO LARGE HAIL/DAMAGING WINDS.
   
   ..KERR.. 02/18/2009
   
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