SPC AC 061731

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1231 PM CDT Sat Jun 06 2020

   Valid 071200Z - 081200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE SUNDAY
   AFTERNOON AND EVENING ACROSS PARTS OF THE EASTERN DAKOTAS AND
   ADJACENT NORTHWESTERN MINNESOTA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE SUNDAY
   THROUGH SUNDAY NIGHT ACROSS PARTS OF THE CENTRAL GULF COAST
   REGION...

   ...SUMMARY...
   Severe thunderstorms are possible across parts of the northern
   plains Sunday through Sunday night.  This may include one or two
   evolving storm clusters across parts of the eastern Dakotas Sunday
   evening, accompanied by a risk for damaging wind gusts, in addition
   to severe hail.  A risk for tornadoes may also develop across the
   central Gulf Coast region in association with the landfall of
   Tropical Storm Cristobal.

   ...Synopsis...
   A belt of westerlies emanating from the mid-latitude Pacific appears
   likely to remain amplified through this period.  While large-scale
   ridging may begin to shift inland of the Pacific coast by late
   Sunday night, downstream large-scale troughing over the
   Intermountain West, Rockies and northern high plains, and ridging
   across the lower northern plains, upper Mississippi Valley/Midwest
   may generally be maintained.  The ridging may broaden eastward
   across the Great Lakes and Ohio valley, with some eastward
   redevelopment of the mid-level high center across the middle
   Mississippi Valley, as significant downstream troughing digs off the
   Atlantic Seaboard.  As this occurs, Cristobal is expected to turn
   northwestward across the north central Gulf of Mexico, into and
   across the Louisiana coast by Sunday night.

   Within the Western troughing, the remnant perturbation of a
   mid-level closed low emerging from the subtropical eastern Pacific
   is forecast to pivot northwestward across the central Canadian/U.S.
   border into the Canadian Prairies early in the period.  This may
   contribute to a developing mid-level low over northern Alberta,
   beneath which the primary, but weakening surface cyclone is forecast
   to migrate to by late Sunday night.  A weak surface front/wind shift
   trailing the cyclone is expected to curve across the international
   border through central North Dakota into northwestern South
   Dakota/northeastern Wyoming by late Sunday afternoon.

   While the stronger upstream short wave perturbations are forecast to
   progress through the larger-scale troughing across the Great Basin
   through northern Rockies, models do suggest a more subtle
   perturbation could rapidly shift north-northeast of the Rockies
   through the north central high plains and Dakotas by early Sunday
   evening, before weak short wave ridging builds in its wake across
   the central into northern plains.  This may be accompanied by the
   development of a secondary low within the pre-frontal surface
   troughing across central South Dakota by early Sunday evening.

   Seasonably moist boundary-layer air returning northward on moderate
   to strong southerly low-level flow ahead of .the surface trough
   appears likely to contribute to large CAPE beneath modestly steep
   mid-level lapse rates.  This will contribute to potential for
   organized severe storm development late Sunday afternoon into Sunday
   night.

   ...Northern Plains...
   Despite relatively warm mid-level temperatures, surface dew point
   increases into the upper 60s/near 70F may contribute to large
   mixed-layer CAPE on the order of 2000-3000+ J/kg with daytime
   heating.  This is expected to be most prominently focused within the
   warm sector to the east of the cold front/pre-frontal surface
   troughing across the eastern Dakotas by late Sunday afternoon.  

   The destabilization will occur in the presence of strong deep-layer
   shear, beneath 50+ kt southwesterly 500 mb flow.  Forcing to support
   thunderstorm initiation is more unclear.  It is possible this may
   mostly await strengthening lower/mid tropospheric warm advection in
   the wake of the subtle mid-level impulse.  This is expected to
   become focused north/northeast of the developing surface low, on the
   nose of warmer and more strongly capping mid-level air advecting
   northward across the plains, before spreading across northeastern
   South Dakota and eastern North Dakota/adjacent northwestern
   Minnesota Sunday evening.  

   Convective evolution probably will include supercells initially,
   posing a risk for severe hail and perhaps a couple of tornadoes,
   before one or two upscale growing, organizing convective systems
   evolve with the risk for damaging wind gusts becoming more
   prominent.

   ...Central Gulf Coast region...
   The inland advection of tropical boundary-layer moisture in the
   presence of enlarging clockwise curved low-level hodographs, with
   the approach and inland migration of Cristobal, probably will be
   accompanied by the risk for the development of supercells capable of
   producing tornadoes, perhaps as early as Sunday afternoon.

   ..Kerr.. 06/06/2020

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