National Weather Service United States Department of Commerce

A Change in the Weather Pattern

The Atmospheric River event has ended for the Northwest, and conditions will be drier for a couple of days. A strong cold front in the East may produce damaging high winds in the central Appalachians and critical fire weather threats. Bitter wind chills across Northeast Alaska and heavy snow in the Southeast will continue, and blizzard conditions are expected to develop in far west-central Alaska. Read More >

Day 4-8 Severe Weather Outlook issued at 0850 UTC on 23 April 2011

ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 230850
   SPC AC 230850
   
   DAY 4-8 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0350 AM CDT SAT APR 23 2011
   
   VALID 261200Z - 011200Z
   
   ...DISCUSSION...
   SUBSTANTIAL SEVERE WEATHER POTENTIAL IS EXPECTED TO SHIFT SLOWLY EWD
   ACROSS THE ERN U.S. DAYS 4-6 /TUE. 4-26 THROUGH THU. 4-28/...AS A
   LARGE UPPER TROUGH PROGRESSES FROM THE CENTRAL U.S. DAY 4 ACROSS THE
   MS VALLEY DAY 5...AND THEN ON EWD THROUGH DAYS 6/7.  MODEL
   DIFFERENCES WITH RESPECT TO TIMING OF THIS FEATURE BEGIN TO EMERGE
   DAY 5...BUT BECOME INCREASINGLY PRONOUNCED THROUGH DAYS 6 AND 7 AS
   THE TROUGH APPROACHES THE E COAST STATES/ERN ATLANTIC.
   
   THE PRIMARY SEVERE THREAT DAY 4 IS PROGGED FROM E TX NEWD ACROSS THE
   ARKLATEX INTO THE MID MS VALLEY...AS A SHORT-WAVE TROUGH DIGS ESEWD
   INTO THIS REGION...WITHIN THE LARGER-SCALE TROUGH.  UNSTABLE AIRMASS
   COMBINED WITH THE ENERGETIC SHORT-WAVE FEATURE AND ASSOCIATED/STRONG
   FLOW FIELD SUGGESTS WIDESPREAD SEVERE WEATHER POTENTIAL -- INCLUDING
   RISKS FOR LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES. 
   
   THE THREAT SHOULD SHIFT E OF THE MS VALLEY INTO THE MID
   SOUTH/SOUTHEAST DAY 5...AS THE SHORT-WAVE FEATURE TAKES ON A NEUTRAL
   TO EVEN NEGATIVE TILT AS IT CROSSES THIS REGION.  AGAIN -- AMPLY
   UNSTABLE AIRMASS COMBINED WITH THE STRENGTH OF THE UPPER SYSTEM AND
   ASSOCIATED FLOW FIELD SUGGESTS WIDESPREAD SEVERE WEATHER CAN BE
   EXPECTED...INCLUDING THE POTENTIAL FOR TORNADOES.
   
   AS MODELS BEGIN DIVERGING SOMEWHAT WITH RESPECT TO TIMING AND
   SMALLER-SCALE DETAILS...DEGREE OF THREAT SHIFTING ACROSS THE
   APPALACHIANS LATE DAY 5 AND INTO DAY 6 BECOMES LESS CERTAIN.  WHILE
   SEVERE WEATHER WILL BE LIKELY WITH THE FRONT EXPECTED TO REACH THE
   ATLANTIC COAST BY THE END OF THE PERIOD...WILL REFRAIN FROM
   HIGHLIGHTING A THREAT AREA THIS FORECAST.
   
   WITH THE FRONT LIKELY OFFSHORE BY THE START OF DAY 7... SEVERE
   WEATHER POTENTIAL ACROSS THE U.S. APPEARS LESS
   WIDESPREAD/SIGNIFICANT AND MUCH MORE UNCERTAIN THROUGH THE END OF
   THE PERIOD.
   
   ..GOSS.. 04/23/2011

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