SPC AC 200532

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1232 AM CDT Sun Jun 20 2021

   Valid 201200Z - 211200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN
   IOWA TO SOUTHERN LOWER MICHIGAN...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   ENHANCED RISK FROM THE MID MISSISSIPPI VALLEY INTO THE LOWER GREAT
   LAKES ALONG WITH PARTS OF THE SOUTHEAST...

   ...SUMMARY...
   Scattered severe storms are expected across the Midwest into the
   lower Great Lakes/upper Ohio Valley. Large hail, severe/damaging
   winds, and a few tornadoes are possible. Damaging winds and a couple
   of tornadoes are also possible across the Southeast.

   ...Midwest to Lower Great Lakes...

   Late Saturday central High Plains convection has spread downstream
   and matured into a significant MCS as it tracks east along the NE/KS
   border. Forward propagation appears to be reasonably similar to the
   latest NAM with the leading edge of the MCS likely spreading across
   southwestern into south-central IA early in the period. One concern
   is how poorly the models are handling the strong, sustained
   convection across northern MO. This activity continues to propagate
   northwest and will likely be absorbed into a larger complex by
   daybreak. The disruptive potential of this interaction is unknown.
   Even so, it appears a corridor of strong instability should evolve
   from northern IL into southern lower MI. Approaching convectively
   induced short-wave trough, strong heating, and the potential for a
   low-level confluence zone to be draped across this region suggest
   the potential for significant severe. Have opted to extend the ENH
   Risk downstream across southern lower MI and adjacent portions of
   northern IN/northwest OH as forecast soundings are impressively
   buoyant and strongly sheared. Profiles favor supercells but the
   early-day MCS will likely continue, in some form, through the day as
   it spreads downstream. If supercells evolve, tornadoes and large
   hail threat will increase with this activity. Otherwise, damaging
   winds can be expected.

   Later in the afternoon, surface heating should contribute to frontal
   convection that will initiate across the upper MS Valley, then
   spread/develop along the wind shift into eastern KS. Steep lapse
   rates, strong surface-6km shear, and abundant instability suggest
   the potential for very large hail with supercells in the wake of the
   early-day MCS.

   ...Southeast...

   Remnants of Claudette continue to shift downstream across AL into
   GA/northern FL. Low-level shear will remain strong from northern FL
   into coastal NC much of the period. While numerous showers/storms
   will be ongoing at daybreak, latest NAM suggests a narrow corridor
   of steeper surface-3km lapse rates within the zone of stronger shear
   from northeast FL through coastal SC. This may increase the
   potential for damaging winds and tornadoes. For these reasons have
   increased severe probabilities across this region.

   ..Darrow/Lyons.. 06/20/2021

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