ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 090858
   SPC AC 090858

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0358 AM CDT Mon May 09 2022

   Valid 121200Z - 171200Z

   ...DISCUSSION...
   Medium-range models continue to depict the northeastward ejection of
   western U.S. troughing across the Rockies and into the northern
   Plains Day 4/Thursday, before shifting across the international
   border into the Canadian Prairie into early Day 5/Friday.

   The trough -- taking on increasing negative tilt as it advances --
   will drive northern Plains cyclogenesis, with the low expected to
   quickly occlude and retrograde northwestward.  The low should reach
   the southeastern Saskatchewan/southwestern Manitoba vicinity by
   Friday morning.

   Within the warm sector of the surface cyclone, a moist boundary
   layer beneath steep lapse rates aloft will yield moderate
   destabilization, allowing widespread storm development as strong
   ascent focuses near/ahead of the low and near the cold front
   crossing the Dakotas during the afternoon.  

   As the flow field aloft responds to the increasing negative tilt of
   the upper trough, some backing in the high-level wind field is
   expected.  Although such a wind profile would not be as conducive to
   highly organized/long-lived supercells, rotating/severe storms are
   nonetheless likely.  Large hail and damaging winds will likely
   become increasingly common through late afternoon and into the
   evening, along with potential for a couple of tornadoes.  Risk
   should spread eastward from the eastern Dakotas into Minnesota into
   the evening, and likely continuing into the overnight hours.

   As the strongest ascent shifts into Canada Day 5/Friday, frontolysis
   is expected with the trailing cold front as it crosses the Upper
   Mississippi Valley.  Models suggest that small spokes of short-wave
   troughing may rotate across the north-central U.S. within the
   westerly/cyclonic flow surrounding the evolving Canadian Prairie
   low.  While this could focus clusters of storms, and some severe
   potential given a remnant unstable airmass ahead of the weakening
   front, confidence is too low to highlight any risk areas. 
   Meanwhile, convection appears likely to extend south-southwestward
   along the weak baroclinic zone, across the Missouri Valley to the
   southern Plains region.  However, modest flow aloft should somewhat
   limit severe potential.

   Days 6-8, the Canada/northern U.S. upper system will move slowly
   eastward, eventually impinging on -- and then merging with -- a
   retrograding upper low moving westward into the Southeast, and then
   northwestward into the Ohio Valley.  The merging of these two
   systems is depicted somewhat differently amongst various models, and
   some lack of clarity is evident with associated evolution of both
   thermodynamic and kinematic fields.  As such, no risk areas will be
   highlighted through latter stages of the period.

   ..Goss.. 05/09/2022

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