SPC AC 230602

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0102 AM CDT Sun Aug 23 2020

   Valid 241200Z - 251200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
   SOUTHEASTERN MINNESOTA SOUTHEASTWARD TO SOUTHWESTERN LOWER
   MICHIGAN...

   ...SUMMARY...
   A few thunderstorms capable of producing locally gusty/damaging
   winds, and possibly hail, may affect portions of the Great Lakes and
   vicinity and into New England Monday.  Some risk for brief/weak
   tornadoes will also exist over south Florida and the Keys, as Laura
   passes to the southwest, and with Marco presuming landfall over
   southeastern Louisiana.

   ...Upper Great Lakes...
   As the trailing portion of a cold front crossing Ontario and Quebec
   sags southward across the Upper Great Lakes region, convection may
   be ongoing at the start of the period -- possibly accompanied by
   low-end wind risk, mainly from northern Wisconsin and Upper Michigan
   east across northern Lower Michigan.

   As this convection spreads east across Lake Huron and into Ontario
   with time, new convective development -- driven by warm advection
   near and atop the southward-moving front -- may occur, across
   portions of southeast Minnesota and southern Wisconsin, and shifting
   southeastward with time.  Given ample CAPE and veering/increasing
   flow with height, risk for large hail is apparent.  Locally damaging
   winds -- and possibly a tornado -- could also occur, if storms near
   the front can remain surface-based during the evening hours.

   ...Lower Great Lakes into New England...
   While it appears that the cold front advancing across Ontario/Quebec
   should remain northwest of the Lower Great Lakes/New England through
   the end of the period, modest heating/destabilization of the
   pre-frontal airmass is expected during the day across New York/and
   into New England.  Gradual height falls and presence of a
   weak/subtle warm-frontal boundary extending northwest-to-southeast
   across northern New York and southern New England may focus a
   cluster of afternoon storms.  Though stronger flow will remain
   across Canada through the day, shear may support potential for gusty
   winds -- and perhaps local tree damage with the afternoon storms.

   Later in the period, storms nearer the advancing front may spill
   across the international border.  While a less unstable boundary
   layer after dark should limit severe risk, strengthening flow aloft
   may be sufficient to maintain low-end risk for wind through much of
   the period.

   ...South Florida and the Keys...
   Track forecasts from the NHC bring Laura west-northwestward across
   western Cuba and into the Gulf of Mexico west of the Keys, which
   would result in increased low-level flow across portions of south
   Florida and the Keys, during the period.  While questions exist with
   respect to the degree -- and breadth -- of convection surrounding
   Laura, after having spent 24 hours over Cuba per the latest track
   forecasts, at least low-end tornado threat would exist based on just
   the increased low-level flow alone.  As such, will introduce 2%/MRGL
   risk across the area, for potential that a couple of rotating cells
   in outer bands shift across the region.

   ...Central Gulf Coast region...
   Latest track forecast for Marco from the NHC suggests landfall by
   Monday afternoon near the mouth of the Mississippi River -- but with
   considerable uncertainty noted.  Presuming the current track
   forecast, some potential for a couple of brief/weak tornadoes could
   evolve over southeast Louisiana, and eastward across Mobile Bay and
   perhaps far western portions of the Florida Panhandle.  This risk
   area will be subject to future changes, given the uncertainty with
   respect to intensity and track of this tropical system.

   ..Goss.. 08/23/2020

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