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Mesoscale Discussion 847
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   Mesoscale Discussion 0847
   NWS Storm Prediction Center Norman OK
   0431 PM CDT Fri May 26 2017

   Areas affected...East-central Illinois and western/northwestern

   Concerning...Tornado Watch 269...

   Valid 262131Z - 262230Z

   The severe weather threat for Tornado Watch 269 continues.

   SUMMARY...A localized tornado threat appears to be increasing across
   east-central Illinois in the short term.

   DISCUSSION...An earlier line of storms over central Illinois (with a
   history of hail and wind damage) has evolved into supercell
   structures over portions of Livingston and McLean counties recently.
    These storms are on the north edge of an area of moderate
   instability (1500-2000 J/kg MUCAPE), with strongly veering wind
   profiles with height and localized vorticity ingest along the warm
   front aiding in updraft rotation with these storms.  It appears that
   the tornado threat with this activity is on the increase in the near
   term, with hail/damaging wind gusts also possible near the strongest

   Farther west, convective overturning has stabilized portions of
   west-central Illinois north of an outflow boundary, although some
   lingering mid-level instability (evidenced by convective towers atop
   the cool low-level airmass on satellite imagery) suggests the severe
   threat may not be completely over.  Additional activity may form
   along the aforementioned outflow boundary in southwestern portions
   of the watch and also in east-central Illinois south of the ongoing
   supercells (Macon, Piatt, and Champaign counties).  This activity
   will pose a threat for all severe modes into the evening, and
   spatial southward and eastward extensions of WW 269 may be needed to
   account for any evolving severe threat with this activity.

   ..Cook.. 05/26/2017

   ...Please see for graphic product...


   LAT...LON   40169040 40559040 40799002 41138931 41268815 41278735
               41228654 41058608 40728595 40478595 40238632 40108724
               39928767 39788819 39798876 39928929 39909002 39999023

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