SPC AC 230725

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0225 AM CDT Mon Jul 23 2018

   Valid 251200Z - 261200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE WEDNESDAY
   AFTERNOON AND EVENING ACROSS PARTS OF THE CENTRAL PLAINS AND MIDDLE
   MISSOURI VALLEY INTO UPPER MIDWEST...

   ...SUMMARY...
   Strong thunderstorms may impact a corridor from the central Plains
   into the middle Missouri Valley and Upper Midwest Wednesday
   afternoon and evening, accompanied by at least some risk for severe
   weather.

   ...Synopsis...
   Models indicate further amplification of ridging within the
   mid-latitude westerlies is possible near the British Columbia coast
   during this period.  As this occurs, broad downstream troughing is
   forecast to continue to gradually dig across and southeast of the
   central Canadian/U.S. border area.  It appears that this will
   include a fairly deep mid-level closed low developing southeastward 
   across northwest Ontario and portions of the Upper Midwest/upper
   Great Lakes region.

   In response to this development, the northeastern periphery of a
   large subtropical high centered over the Southwest will become
   increasingly suppressed across the mid Missouri Valley into the high
   plains east of the northern Colorado and Wyoming Rockies.  And
   lingering downstream mid-level troughing to the east of the
   Mississippi Valley is expected to become increasingly sheared across
   the Appalachians and Atlantic Seaboard, as subtropical ridging over
   the western Atlantic maintains strength.

   At the present time, any appreciable severe weather potential
   Wednesday through Wednesday night seems likely to accompany the
   digging upper impulse, across parts of the central Plains and middle
   Missouri Valley into the Upper Midwest.  Preceding an associated
   southeastward advancing cold front, a corridor of moderate boundary
   destabilization appears possible by late Wednesday afternoon, in the
   presence of moderate to strong deep layer shear beneath 30-50 kt
   northwesterly mid-level flow.  This will provide potential for
   severe storm development that may continue into Wednesday evening
   while spreading southeastward.  However, there are indications that
   lingering warm advection driven convection from Tuesday night,
   and/or its associated outflow, may complicate destabilization
   Wednesday, particularly across the central Plains.  Coupled with
   continuing spread within/among the various model output concerning
   synoptic developments, too much uncertainty exists for more than 5
   percent severe probabilities.

   ..Kerr.. 07/23/2018

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