SPC AC 180600

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Sat Jul 18 2020

   Valid 181200Z - 191200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   THE UPPER MIDWEST AND WESTERN GREAT LAKES...

   ...SUMMARY...
   Severe storms should occur Saturday across portions of the Upper
   Midwest and Great Lakes vicinity. Damaging winds and large hail
   appear to be the main hazards with these storms, some of which could
   be significant. A few tornadoes are also possible.

   ...Upper Midwest/Great Lakes...

   A well-organized, potentially severe MCS will be ongoing at 12z
   Saturday from the Upper Peninsula of MI across WI, with an
   associated outflow boundary likely extending from the MCS in the
   vicinity of southern MN. Uncertainty in the position and strength of
   the outflow is the primary question with this forecast. 

   A shortwave trough embedded within moderately strong westerlies will
   move into the northern Plains Saturday and Saturday night. Strong
   instability will once again develop along and south of the remnant
   outflow boundary and in advance of an eastward-moving cold front
   where very rich low-level moisture lies beneath steep (8-8.5 deg
   C/km) mid-level lapse rates. By afternoon the cold front should
   extend from western MN across central NE and into northeast CO, with
   a surface trough extending across western KS.

   Thunderstorms are expected to develop in the vicinity of the cold
   front/outflow intersection by late afternoon, where CINH should be
   overcome through sustained convergence/lift. Initially, scattered
   discrete supercell storms will be capable of large/very large hail
   and severe winds. The magnitude of instability and potential for
   locally enhanced low-level SRH in the vicinity of the outflow
   boundary may pose a risk for tornadoes through early evening. With
   time, upscale growth into a severe MCS is expected with a risk for
   damaging winds, potentially significant, large hail, and
   line-embedded circulations capable of brief QLCS tornadoes.

   An Enhanced Risk was strongly considered over portions of the upper
   Midwest/western Great Lakes for Saturday, however with uncertainty
   in the location of key surface features and influence of ongoing
   MCS, will defer any possible higher severe probabilities to
   subsequent outlooks. 

   ...NE/KS southwest into TX Panhandle/northeast NM...

   Scattered thunderstorms will be possible during the
   afternoon/evening along the cold front and surface trough, where
   strong daytime heating will result in a deep mixed layer and
   inverted-v thermal profiles. Isolated damaging gusts will be the
   primary severe threat.

   ...Western/central ND...

   Isolated hail and strong wind gusts will be possible with storms
   developing during the afternoon near a weak surface trough, in
   association with relatively cool mid-level thermal profiles and lift
   associated within the left exit region of an approaching upper-level
   speed max.

   ..Bunting/Karstens.. 07/18/2020

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