Storm Prediction Center Mesoscale Discussion 509

   Mesoscale Discussion 0509
   NWS Storm Prediction Center Norman OK
   0954 PM CDT Sun Apr 20 2025

   Areas affected...portions of northern Illinois

   Concerning...Tornado Watch 157...

   Valid 210254Z - 210430Z

   The severe weather threat for Tornado Watch 157 continues.

   SUMMARY...The severe threat continues across Tornado Watch 157. A
   couple of severe gusts are the main concern, though a tornado cannot
   be ruled out.

   DISCUSSION...A primary band of convection persists amid very strong
   forcing accompanying an approaching surface low and upper-level jet
   streak. Despite scant buoyancy, the latest LOT VAD shows a hodograph
   with impressive size and curvature, indicating strong low-level wind
   shear, driven by very strong flow just above the surface. While
   decreasing lightning trends suggest that storms are weakening, the
   intense low-level flow/shear suggests that damaging gusts may still
   occur wherever downward momentum transport may occur. A tornado also
   remains possible if a rotating updraft can ingest any remaining
   surface-based buoyancy.

   ..Squitieri.. 04/21/2025

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

   ATTN...WFO...LOT...ILX...DVN...

   LAT...LON   40568839 40928885 41308911 41708931 41948922 41998888
               41828838 41428803 40988774 40608769 40498805 40568839 

   MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH
   MOST PROBABLE PEAK WIND GUST...65-80 MPH
   MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN