Apr 20, 2011 0600 UTC Day 1 Convective Outlook
Updated: Wed Apr 20 05:25:46 UTC 2011
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20110420 1200 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20110420 1200 UTC Day 1 Tornado Probabilities Graphic
Torndao Legend Image
Probabilistic Damaging Wind Graphic
20110420 1200 UTC Day 1 Damaging Wind Probabilities Graphic
Wind Legend Image
Probabilistic Large Hail Graphic
20110420 1200 UTC Day 1 Large Hail Probabilities Graphic
Hail Legend Image
   SPC AC 200522
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1222 AM CDT WED APR 20 2011
   
   VALID 201200Z - 211200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN TX ENEWD ACROSS THE
   MID SOUTH...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MID-ATLANTIC
   REGION...
   
   ...SYNOPSIS...
   RELATIVELY FLAT UPPER TROUGH CROSSING THE CENTRAL U.S. EARLY IS
   FORECAST TO SHIFT INTO/ACROSS THE NORTHEAST THIS PERIOD...WITH MORE
   ZONAL/WLY FLOW ALOFT LEFT ACROSS MUCH OF THE COUNTRY IN ITS WAKE. 
   MEANWHILE...A TROUGH PROGRESSING TOWARD THE WRN U.S. IS EXPECTED TO
   REACH THE COAST LATE IN THE PERIOD.
   
   AT THE SURFACE...A COLD FRONT IS PROGGED TO CROSS THE NRN AND
   CENTRAL APPALACHIANS THROUGH THE AFTERNOON...WHILE SHIFTING MORE
   SLOWLY SEWD ACROSS THE MID SOUTH INTO THE GULF COAST STATES/SWD INTO
   TX.  BY THE END OF THE PERIOD...THE NRN PORTION OF THE FRONT WILL
   LIE OVER THE WRN ATLANTIC OFF NEW ENGLAND AND THE MID-ATLANTIC
   REGION...WHILE STRETCHING WWD ACROSS THE GULF COAST STATES INTO TX.
   
   ...ERN TX ENEWD ACROSS THE GULF COAST STATES...
   STORMS SHOULD BE ONGOING AT THE START OF THE PERIOD INVOF THE
   SURFACE FRONT...AND EXPECT PERSISTENT REDEVELOPMENT TO OCCUR THROUGH
   THE AFTERNOON AS DIURNAL HEATING/DESTABILIZATION INCREASE -- DESPITE
   THE LACK OF A FORCING MECHANISM ALOFT.
   
   WHILE FLOW ALOFT SHOULD ALSO SLACKEN ACROSS THIS REGION A BIT DURING
   THE AFTERNOON...PRESENCE OF THE FRONT AND AMPLY MOIST/UNSTABLE
   AIRMASS SUGGEST STRONGER STORMS WILL BE CAPABLE OF LOCALLY DAMAGING
   WINDS AND MARGINAL HAIL INTO THE EVENING.
   
   ...MID-ATLANTIC REGION...
   POTENTIAL FOR CONVECTIVE DEVELOPMENT REMAINS A QUESTION ATTM...AS
   WEAKENING CONVECTION EARLY IN THE PERIOD SHOULD RESULT IN EXPANSIVE
   CLOUD COVER ACROSS THIS REGION.  WHILE MODELS FORECAST AFTERNOON
   DESTABILIZATION AHEAD OF THE ADVANCING FRONT...ATTM IT APPEARS THAT
   WITH STRONGER FORCING ALOFT SHIFTING NE OF THIS REGION AND THE
   LIKELIHOOD FOR CLOUDINESS TO RETARD HEATING...CONVECTIVE DEVELOPMENT
   MAY BE LESS WIDESPREAD/VIGOROUS THAN EXPECTED EARLIER.
   
   HOWEVER...WILL MAINTAIN SLIGHT RISK FOR WIND...AS ANY POCKETS OF
   HEATING COULD PERMIT STORM DEVELOPMENT ALONG/AHEAD OF THE FRONT
   WHICH -- GIVEN STRENGTH OF THE FLOW FIELD ALOFT -- WOULD LIKELY
   RESULT IN LOCALLY DAMAGING WINDS.
   
   ...OK AND VICINITY...
   STRENGTHENING SLY LOW-LEVEL JET AND RESULTING ISENTROPIC UPGLIDE MAY
   RESULT IN ELEVATED CONVECTIVE DEVELOPMENT LATE IN THE PERIOD.  WITH
   STEEP LAPSE RATES ALOFT...INSTABILITY SHOULD BE SUFFICIENT -- IN
   CONJUNCTION WITH MODERATE WLYS ALOFT -- TO YIELD A FEW STRONGER
   STORMS.  THUS...WILL MAINTAIN LOW PROBABILITY HAIL THREAT ACROSS
   THIS REGION.
   
   ..GOSS/COHEN.. 04/20/2011
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z