SPC AC 270731

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0231 AM CDT Tue Jun 27 2023

   Valid 291200Z - 301200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE GREAT LAKES AND LOWER OHIO VALLEY...

   ...SUMMARY...
   A severe threat, with a potential for wind damage and large hail,
   appears likely to develop on Thursday across parts of the southern
   Great Lakes region into the lower Ohio Valley. An isolated severe
   threat may also develop in parts of the central High Plains.

   ...Great Lakes/Lower Ohio Valley...
   A mid-level anticyclone will be in place across the southern U.S. on
   Thursday. North of the anticyclone, a subtle shortwave trough, and
   an associated 40 to 55 knot mid-level jet, will move eastward
   towards the southern Great Lakes. At the surface, a cold front will
   advance southeastward across the Upper Midwest. Ahead of the front,
   surface dewpoints will be in the upper 60s and lower 70s F across
   much of the mid Mississippi Valley. By afternoon, an axis of strong
   instability is forecast to develop from northern Missouri eastward
   into central Illinois, with an instability axis extending
   southeastward into the Tennessee Valley. Thunderstorms appear likely
   to develop on the northwestern edge of the moist airmass along and
   near the front in the afternoon. The storms are forecast to move
   southeastward into the stronger instability. An MCS will be possible
   by early evening.

   NAM forecast soundings around 21Z in the Chicago Metro, near the
   instability axis, have MLCAPE peaking around 4000 J/kg, with 0-6 km
   shear near 45 knots. This, combined with steep lapse rates around
   8.0 C/km will be favorable for supercells with large hail. A wind
   damage threat will also be possible, especially if a cold pool can
   organize. An isolated tornado threat could also develop. The main
   uncertainty is concerning convective coverage. At this time, the
   models are mostly in agreement that a cluster will initiate in
   southern Wisconsin and move southeastward into the stronger
   instability across northern Illinois. Further to the northeast, more
   uncertainty exists for not only convective initiation but
   instability as well. There is considerable spread in the models for
   these two factors over lower Michigan. Still, an isolated severe
   threat could develop in lower Michigan if enough instability
   materializes.

   ...Central High Plains...
   An upper-level trough will develop across the Intermountain West on
   Thursday, as mid-level flow remains from the southwest across the
   central High Plains. At the surface, upslope flow is forecast across
   the central High Plains, and this will ensure that moisture is
   pushed westward toward the higher terrain of north-central Colorado.
   As surface heating takes place, thunderstorms may form in the higher
   terrain of north-central Colorado or further northeast in western
   Nebraska. Moderate instability and strong deep-layer shear is
   evident on forecast soundings in these two areas, suggesting a
   severe threat will be possible in each. The main uncertainty is
   which of the two areas will be favored for convective initiation.
   Concerning convective potential, the NAM has greater potential
   further west with the ECMWF further northeast. If the model
   solutions can become in better agreement concerning this, then a
   slight risk may need to be added in the next outlook update.

   ..Broyles.. 06/27/2023

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