SPC AC 240723

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0223 AM CDT Wed Jun 24 2020

   Valid 261200Z - 271200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE MID
   MISSOURI VALLEY TO THE GREAT LAKES...

   ...SUMMARY...
   Scattered to isolated thunderstorms posing at least local risk for
   damaging winds and hail will be possible from the central Plains
   east-northeastward across the Midwest to the Great Lakes Friday
   afternoon and evening.

   ...Synopsis...
   A trend toward more westerly/zonal flow aloft is expected Friday, as
   the persistent Quebec upper low weakens, and cyclonic flow south of
   the low pivots off the Northeast U.S. coast.  A short-wave trough
   within the westerlies will cross the central portion of the country
   through the period.

   At the surface, a cold front will become elongated in a more
   northeast-to-southwest manner, as the northern portion of the front
   crossing the Great Lakes region moves eastward while trailing
   portions of the front move more slowly southward across the central
   Plains.  Meanwhile, a second cold front is forecast to advance
   inland over the Northwest, ahead of a mid-level short-wave trough
   digging southeastward out of the Gulf of Alaska.

   ...Mid MO/Mid MS Valleys to the Great Lakes...
   Thunderstorms are forecast to be ongoing across portions of the risk
   area at the start of the period, casting some uncertainty with
   respect to subsequent areas that may amply destabilize to foster
   new/afternoon storm development near the advancing cold front.  The
   greatest uncertainty appears to exist over the Wisconsin/Michigan
   vicinity, where convection may linger through much of the morning
   and into the afternoon.  Still, it appears that at least weak
   destabilization will occur over the Lower Lakes ahead of the front,
   and likely more substantial instability near and ahead of the
   boundary with southwestward extent.

   As convection redevelops ahead of the front during the afternoon,
   enhanced/westerly flow aloft through the lower and middle
   troposphere expected across the region will be sufficient for
   organized storms -- possibly evolving locally into
   fast/eastward-moving bands.  Along with some hail potential, locally
   damaging winds appears likely to be the favored severe risk. 
   Convection should continue through the overnight hours -- spreading
   eastward across the Midwest and Lower Great Lakes with time, but
   with severe risk likely waning gradually as the airmass stabilizes
   with time.

   ...Central and southern High Plains...
   Late afternoon/early evening thunderstorm development is expected
   over the Front Range, as low-level easterly upslope flow evolves
   just north of a southward-moving cold front.  Moderate westerly flow
   aloft atop low-level southerlies will likely result in sufficient
   shear for a few longer-lived updrafts, and with a deep mixed layer
   expected over the High Plains, storms moving off the higher terrain
   will be capable of locally strong wind gusts.  Though a developing
   low-level jet could permit some upscale growth as storms move
   southward/southeastward during the evening -- possibly enhancing
   wind risk locally, will introduce only 5% wind probability at this
   time.

   ..Goss.. 06/24/2020

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