SPC AC 101938

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0238 PM CDT Mon Aug 10 2020

   Valid 102000Z - 111200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN
   ILLINOIS...SOUTHEAST WISCONSIN...NORTHWEST INDIANA...FAR SOUTHWEST
   LOWER MICHIGAN...

   ...SUMMARY...
   A derecho producing significant damaging winds will persist across
   much of northern Illinois and possibly far southern Wisconsin, and
   into northern Indiana and southern Lower Michigan this evening.

   ...Northern IL...southeastern WI...northern Indiana...southwestern
   Lower Michigan...
   A Derecho will continue east across northern Illinois, at speeds
   around 60 mph. Many reports of 60-80 mph winds have been recorded
   along with a few over 100 mph as it moved across Iowa and crossed
   the MS River, with some areas experiencing long duration of severe
   winds over 50 kt.

   The environment remains favorable ahead of the Derecho as
   temperatures continue to warm. Modified midday soundings show steep
   midlevel lapse rates and MLCAPE over 3000 J/kg. This will prove
   sufficient to maintain a severe wind threat through the Chicago
   area, including northwest Indiana and parts of Lower Michigan.

   For more information see mesoscale discussions 1455 and 1456.

   ..Jewell.. 08/10/2020

   .PREV DISCUSSION... /ISSUED 1057 AM CDT Mon Aug 10 2020/

   ...IA to the Midwest...
   A pair of impulses embedded within a shortwave trough over the Upper
   Midwest will rapidly progress east. A 50+ kt jetlet should persist
   from eastern SD into southern WI through early evening. An intense
   MCS with a well-developed rear-inflow jet is ongoing to the south of
   the mid-level jet across central IA. Very steep mid-level lapse
   rates around 9 C/km per 12Z OAX and DVN soundings along with robust
   boundary-layer heating ahead of it should support maintenance of
   this MCS this afternoon. On the fringe of the stronger mid-level
   westerlies, a pronounced bow should sweep eastward across eastern IA
   and the northern IA vicinity. The MCS should enlarge as well as
   convection develops northeast along a surface front into southern
   WI. For more in-depth discussion of the short-term severe threat,
   please see MCD 1450.  

   Given large buoyancy and steep low to mid-level lapse rates within
   the gradient of moderate to strong mid-level westerlies, potential 
   will exist for a derecho with intense severe gusts and widespread
   wind damage across parts of central to eastern IA into northern IL
   and far southern WI. 

   The MCS will likely persist east into Lower MI and IN while
   developing southwestward into a high MLCAPE environment to the
   southwest in central and southern IL. While deep-layer shear will
   drop off with southern extent and steeper lapse rates with eastern
   extent, a severe risk mainly in the form of damaging winds will
   probably continue on a more scattered basis this evening in the
   Midwest before eventual decay tonight.

   ...MO to the TX Panhandle..
   Pockets of strong surface heating will result in a plume of large
   buoyancy ahead of a southward-moving cold front. Scattered late
   afternoon and evening multicell thunderstorms are expected to
   develop, with the strongest cells primarily capable of severe wind
   gusts.

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