ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 030850
   SPC AC 030850

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0350 AM CDT Wed Jun 03 2020

   Valid 061200Z - 111200Z

   ...DISCUSSION...
   ...Day 4/Sat - Eastern MT into Western ND/SD...

   An intense shortwave impulse embedded in the larger-scale western
   upper trough will eject north/northeast from the Four Corners
   vicinity to the northern High Plains on Saturday. In response, a
   surface low will deepen over MT with a surface trough extending into
   the northern and central High Plains. Strong south/southeasterly low
   level flow will transport a swath of richer boundary-layer moisture
   northwest across parts of the western Dakotas and eastern/central
   MT. Strong vertical shear will overlap with steep midlevel lapse
   rates and moderate instability, and strong to severe storms appear
   likely from late afternoon into the overnight hours. All severe
   hazards appear possible with forecast soundings showing favorable
   conditions for supercells. An increasing low level jet during the
   evening and overnight hours suggests potential for upscale growth
   during the nighttime hours, which would increase the threat for
   damaging winds across parts of northeast MT into the western
   Dakotas. 

   ...Day 4/Sat - Mid-Atlantic Vicinity...

   An upper trough over Ontario and Quebec will deepen across the
   Northeast and Mid-Atlantic vicinity on Saturday. A moist boundary
   layer will be in place as a cold front develops eastward across the
   region during the morning and afternoon. Some strong to severe storm
   potential appears possible, however guidance varies with regards to
   coverage and intensity. Uncertainty remains too high at this time to
   include 15+ percent severe probabilities, but they may become
   necessary in later outlooks.

   ...Day 5/Sun - Eastern Dakotas into western MN...

   Moisture will stream northward across eastern portions of the
   northern/central Plains on increasing southerly low level flow ahead
   of a surface low over the northern High Plains. Some convection
   could be ongoing during the morning as a continuation of an MCS from
   the Day 4/Sat period over parts of ND or MN. Nevertheless, a very
   moist and unstable environment is expected across the eastern
   Dakotas into western MN. As a surface low over eastern WY/MT shifts
   eastward into the western Dakotas, convection is expected to
   redevelop from late Sunday afternoon into Sunday night. Initial
   supercells are possible before another round of upscale growth into
   a bowing MCS develops overnight into western MN. The southward
   extent of severe potential is uncertain, but an isolated threat
   could develop into portions of NE along a surface trough, and severe
   probabilities may need to be added to this area in subsequent
   outlooks. 

   ...Days 5-8/Sun-Wed - Lower MS Valley to Upper Great Lakes...

   There is quite a bit of uncertainty surrounding the evolution of
   what is currently Tropical Storm Cristobal. The TS is forecast by
   the National Hurricane Center to be near the LA coast Sunday night.
   Beyond this, the remains of the system are expected to eventually
   merge with the western upper trough as it ejects eastward into the
   Plains early next week, breaking down the upper ridge and allowing
   the tropical system to develop northward from the Gulf coast. Some
   severe threat will likely accompany this process from the lower/mid
   MS Valley to the Upper Great Lakes early to middle of next week.
   However, uncertainty is too high, precluding severe probs at this
   time.

   ..Leitman.. 06/03/2020

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