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< Day 3 Outlook    
Day 4-8 Severe Weather Outlook Issued on Sep 21, 2018
Updated: Fri Sep 21 08:51:03 UTC 2018
D4-8 D4 D5 D6 D7 D8
 Population  Cities  CWAs  Interstates  Counties  ARTCC  FEMA Regions

D4Mon, Sep 24, 2018 - Tue, Sep 25, 2018 D7Thu, Sep 27, 2018 - Fri, Sep 28, 2018
D5Tue, Sep 25, 2018 - Wed, Sep 26, 2018 D8Fri, Sep 28, 2018 - Sat, Sep 29, 2018
D6Wed, Sep 26, 2018 - Thu, Sep 27, 2018 (All days are valid from 12 UTC - 12 UTC the following day)
Note: A severe weather area depicted in the Day 4-8 period indicates 15%, 30% or higher probability for severe thunderstorms within 25 miles of any point.
PREDICTABILITY TOO LOW is used to indicate severe storms may be possible based on some model scenarios. However, the location or occurrence of severe storms are in doubt due to: 1) large differences in the deterministic model solutions, 2) large spread in the ensemble guidance, and/or 3) minimal run-to-run continuity.
POTENTIAL TOO LOW means the threat for a regional area of organized severe storms appears unlikely (i.e., less than 15%) for the forecast day.
 Forecast Discussion

   ACUS48 KWNS 210849
   SPC AC 210849

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0349 AM CDT Fri Sep 21 2018

   Valid 241200Z - 291200Z

   Latest runs of the medium-range models appear to be in good
   agreement trough day 7 (Thursday 9-27), with respect to large-scale
   pattern evolution.  On days 4-5 (Monday and Tuesday), an upper
   trough is forecast to move gradually eastward across the central
   U.S., while a second trough -- on the western fringe of larger-scale
   cyclonic flow -- begins to dig southeastward across western Canada. 
   By day 6 (Wednesday), as the initial trough shears quickly
   east-northeastward across eastern Canada, the digging western trough
   is forecast to ride southeastward into the long-wave trough over the
   central U.S. -- eventually rotating eastward across the Upper Great
   Lakes and ito eastern Canada through day 7 (Thursday).

   At the surface, a cold front -- associated with the initial upper
   trough -- is forecast to sweep east across the northern and central
   Plains U.S. day 4, the Great Lakes/Midwest day 5, and then the
   Northeast day 6.  Meanwhile, a second front -- associated with the
   subsequent/digging trough -- is forecast to cross the northern and
   central Plains day 6, and then the Great Lakes/Midwest Day 7 in a
   similar manner as the initial front.  While both of these fronts
   will likely be accompanied by an increase in convective risk, the
   second front appears at this time to be following too
   closely/quickly the initial boundary, so as to preclude ample
   moisture return/destabilization potential, and thus severe risk with
   the second front may remain limited.  

   However, more appreciable severe weather potential appears to exist
   with the initial front, particularly day 4 -- from the central
   Plains to western portions of the Upper Great Lakes, and day 5 from
   the Ozarks to the Great Lakes.  Some risk may continue Day 6 into
   the Northeast, but risk appears lesser at this time.  Meanwhile,
   limited risk may redevelop over the central Plains day 6 ahead of
   the next front, but -- as mentioned earlier -- questions regarding
   moisture return ahead of that second front preclude the introduction
   of a day 6 outlook area over the central Plains at this time.

   ..Goss.. 09/21/2018


To retrieve previous Day 4-8 convective outlooks, enter the date YYYYMMDD (e.g., 20050310 for March 10, 2005.)
Data available since March 8, 2005.
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Page last modified: September 21, 2018
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