Mesoscale Discussion 0484
   NWS Storm Prediction Center Norman OK
   0625 PM CDT Fri Apr 17 2026

   Areas affected...Northwest Illinois

   Concerning...Tornado Watch 129...131...

   Valid 172325Z - 180130Z

   The severe weather threat for Tornado Watch 129, 131 continues.

   SUMMARY...A transition to a predominantly linear storm mode is
   likely underway and will result in an uptick in severe wind
   potential as well as embedded mesovorticies downstream across
   central/northern Illinois.

   DISCUSSION...Imagery out of KDVN shows signs of cold pool
   consolidation and expansion as convection continues to cluster and
   grow upscale, likely indicating the transition from semi-discrete
   cells and clusters to a more consolidated linear storm mode. Over
   the next couple of hours one or more organized lines should emerge
   across central to north-central IL. This will be accompanied by an
   increase in severe wind potential as well as the possibility of
   embedded mesovorticies, especially given steadily strengthening
   low-level flow/improving wind shear noted in downstream VWPs.
   Localized corridors of enhanced wind, and perhaps tornado, potential
   are expected where line-preceding convection (noted in west-central
   IL) eventually intersect the developing line, and could result in
   localized surges accompanied by swaths of stronger (potentially
   significant) winds.

   ..Moore.. 04/17/2026

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

   ATTN...WFO...LOT...ILX...MKX...LSX...DVN...

   LAT...LON   40419175 40709132 41209087 41579060 41979046 42249042
               42359025 42528902 42488881 42368866 42168867 41868873
               41508878 41168882 40778894 40478917 40268950 40099007
               39999048 39989091 39989136 40039167 40169180 40259182
               40419175 

   MOST PROBABLE PEAK TORNADO INTENSITY...100-130 MPH
   MOST PROBABLE PEAK WIND GUST...65-80 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN