SPC AC 261626

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1126 AM CDT Fri Jun 26 2020

   Valid 261630Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   AND EVENING FROM EASTERN IA ACROSS SOUTHERN WI/NORTHERN IL TO
   NORTHERN IN AND SOUTHERN 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.

   ...Synopsis...
   A midlevel shortwave trough over IA/southern MN, which was enhanced
   by overnight convection, will continue eastward to Lower MI by early
   tonight and western NY/northwestern PA by 12z Saturday.  Some
   convection is ongoing in the zone of ascent/low-level warm advection
   preceding the midlevel trough from eastern IA into southern
   WI/northern IL.  Cloud breaks in the wake of this convection will
   allow surface temperatures to warm into the 80s, with boundary-layer
   dewpoints of 68-72 F.  Additional storm development is expected by
   early-mid afternoon near a weak surface wave immediately in advance
   of the midlevel trough, and these storms should grow into a
   cluster/MCS this afternoon while spreading eastward across northern
   IL/southern WI, and reach southern Lower MI and vicinity by late
   evening.  Damaging winds will be the main threat with this
   convection given MLCAPE near 1500 J/kg and a belt of 50 kt in the
   700-500 mb layer.  The stronger initial storms could produce large
   hail, and a tornado or two will be possible with embedded
   circulations in the cluster/MCS. 

   ...CO Front Range this afternoon/evening...
   A post-frontal, upslope flow regime will establish today across
   eastern CO, as low-level flow veers from more northerly to easterly
   by mid-late afternoon.  Surface dewpoints will tend to mix into the
   47-50 F range by mid afternoon since surface heating will be strong,
   with moderate buoyancy expected.  Storm initiation is expected along
   the Front Range by 20-21z, and storms will subsequently spread
   east-southeastward across eastern CO through late evening.  MLCAPE
   near 1500 J/kg and effective bulk shear of 30-35 kt will support
   supercells initially with the threat for large hail, with some
   tendency for upscale growth into clusters and more of a damaging
   wind threat this evening. 

   ...Southern IA to KS this evening into tonight...
   In the wake of the primary shortwave trough over IA/MN, a surface
   cold front will drift slowly southeastward across IA/NE/KS.  The
   richer low-level moisture will persist along the front from
   northeast KS into IA, while the hottest surface temperatures and
   deepest mixing will occur across central KS.  The net result will be
   a corridor of MLCAPE near or above 2500 J/kg with weakening
   convective inhibition.  With a lack of larger-scale forcing for
   ascent (aside from a small/weakening MCV now over northeast KS),
   thunderstorm initiation along the front may be delayed until this
   evening from parts of southern IA into northern/central KS.  The
   moderate-strong buoyancy and midlevel lapse rates of 8 C/km or
   greater will support both strong updrafts and downdrafts, with a mix
   of multicell clusters and some marginal supercell expected based on
   effective bulk shear of 25-30 kt.  Large hail and damaging gusts
   will be the main threats from this evening into tonight.

   ..Thompson/Wendt.. 06/26/2020

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