SPC AC 261248

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0748 AM CDT Fri Jun 26 2020

   Valid 261300Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS EASTERN
   IA...NORTHERN IL/IN...SOUTHERN WI/LOWER MI...

   ...SUMMARY...
   Severe thunderstorms with damaging winds, large hail, and a couple
   tornadoes are most probable from eastern Iowa east into southern
   Lower Michigan and far northern Indiana, mainly between 3 to 11 PM
   CDT.

   ...IA to southern Lower MI and northern OH...
   An MCV near the southwest MN/northwest IA border will track east and
   be the primary focus for clusters of renewed storm development
   near/south of it this afternoon. Scattered convection is already
   ongoing across parts of IA, southeast MN into southern WI/northern
   IL. This activity and residual cloud cover will likely limit the
   northeast extent of destabilization in northeast WI and most of MI.
   More robust boundary-layer heating will occur to the south/southwest
   amid an influx of mid to upper 60s surface dew points ahead of a
   weak cold front. This should yield a moderately unstable air mass as
   far northeast as southern IA to perhaps northern IL with MLCAPE
   approaching 1500-2500 J/kg along the fringe of steeper mid-level
   lapse rates.

   Initial midday to early afternoon storm development is expected near
   the immediate MCV along the periphery of surface-based
   destabilization. This activity should spread east-southeast while
   additional storms form southwest near the surface front in eastern
   to southern IA by late afternoon. 25-35 kt effective shear will
   support organized multicells and a few supercells with large hail as
   an initial hazard. With guidance consistently indicating
   strengthening of 850-700 mb winds during the afternoon to early
   evening, yielding weakening of flow between 700-300 mb, upscale
   growth into one or more eastward-propagating clusters is likely.
   This could yield an uptick in damaging wind and brief tornado
   potential during the early to mid evening prior to convection waning
   later tonight towards the Lower Great Lakes.

   ...Lee of the CO Rockies into the central Great Plains...
   Low-level upslope flow is expected to the north of the trailing cold
   front that should become quasi-stationary near the Raton Mesa
   east-northeast towards the KS/NE/MO border area this afternoon. This
   will yield scattered thunderstorms developing along the Front Range
   by early afternoon. The presence of low 50s surface dew points
   beneath steep mid-level lapse rates should promote moderate buoyancy
   with MLCAPE reaching 1000-1500 J/kg by mid afternoon. Guidance is
   consistent in depicting a belt of confluent mid-level westerlies,
   likely yielding 35-45 kt effective shear. Multiple supercells with
   large hail and a brief tornado are the primary threats, which will
   likely affect the I-25 corridor. Storm-scale consolidation will
   probably result in one or more eastward-propagating clusters across
   eastern CO this evening as a southerly low-level jet increases over
   the southern High Plains. This should yield sporadic measured severe
   wind gusts as the clusters spread into western KS prior to a
   substantial increase in MLCIN and eventual weakening overnight. 

   Separately, at least isolated late day/evening storms should develop
   near the stalled front in KS northeast towards the MO/NE border.
   While deep-layer shear will be comparatively modest in this area,
   abundant buoyancy will offer a risk for large hail and severe gusts
   as well.

   ..Grams/Gleason.. 06/26/2020

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