Mesoscale Discussion 1679
   NWS Storm Prediction Center Norman OK
   0530 AM CDT Sun Sep 06 2020

   Areas affected...Central/Eastern IA...Northern IL

   Concerning...Severe Thunderstorm Watch 487...

   Valid 061030Z - 061200Z

   The severe weather threat for Severe Thunderstorm Watch 487
   continues.

   SUMMARY...Strong to severe storms capable of hail and/or damaging
   wind gusts will continue for the next few hours.

   DISCUSSION...Outflow from the ongoing thunderstorms has become
   defined over the past hour or so, and is not readily identifiable in
   radar imagery. This outflow has also led to a modification of the
   warm front, with the outflow acting as an effective cold front
   across central/eastern IA into northwest IL. Radar trends over the
   past hour have also generally shown more transient updrafts, adding
   more evidence to the outflow-dominant character of the storms. The
   exceptions to this trend are ongoing cluster just east of DVN and
   the cell in Grundy County IA. Both of these storms have shown a bit
   more persistence/organization. Storm cluster east of DVN was
   responsible for a 51 kt gust about an hour ago as it went through
   DVN.

   Warm-air advection over the the outflow will continue to lift
   parcels to their LFC, supporting the development of new updrafts, as
   well as aiding in the persistence of ongoing storms. Large hail will
   be possible within the newer updrafts, while strong outflow could
   produce damaging wind gusts as storms collapse. Continued
   eastward/southeastward motion will take the convective system east
   of the stronger low-level flow, likely leading to gradually
   diminishing storm intensity and longevity. Even so, additional areas
   may need to be added to the watch in central IL before this
   weakening trend sufficiently reduces the severe threat.

   ..Mosier.. 09/06/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...LOT...ILX...MKX...DVN...ARX...MPX...DMX...

   LAT...LON   41939422 43649421 42298934 40588935 41939422