SPC AC 021956

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0256 PM CDT Tue Jul 02 2019

   Valid 022000Z - 031200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
   SOUTHERN MT/NORTHERN WY TO THE DAKOTAS...

   ...SUMMARY...
   The most likely region for scattered severe thunderstorms is from
   parts of southern Montana and northern Wyoming east-northeast into
   parts of the Dakotas. The greatest potential for a couple tornadoes
   exists across southwest North Dakota and northwest South Dakota.
   Otherwise, large hail and severe wind gusts are possible this
   afternoon into the overnight.

   ...Discussion...
   Only 1 minor change was made to the previous outlook.  Included the
   eastern IN/southwest OH vicinity in 5-percent wind probabilities
   based in part on measured severe gusts and an unstable airmass
   located downstream of the active thunderstorms in this general area.

   ..Smith.. 07/02/2019

   .PREV DISCUSSION... /ISSUED 1128 AM CDT Tue Jul 02 2019/

   ...Northern Rockies/High Plains to Dakotas...
   A shortwave trough over western OR/WA will drift eastward yielding
   weak downstream height falls across the northern Rockies/adjacent
   High Plains amid a belt of 30-50 kt 500-mb southwesterlies. A cold
   front from northeast ND to far southern MT will stall as surface
   cyclogenesis ensues in the lee of the Big Horns in northeast
   Wyoming. 

   12Z soundings ahead of the front sampled relatively modest
   boundary-layer moisture for early July, but persistent southeasterly
   low-level winds should maintain surface dew points in the upper 50s
   to lower 60s at peak heating near the WY/MT/SD/ND border region.
   Beneath a plume of steep mid-level lapse rates, a corridor of MLCAPE
   from 1500-2500 J/kg is anticipated ahead of the cyclone along the
   front. Deep-layer shear will be maximized in this same corridor,
   with 35-45 kt effective values supportive of supercells as storms
   develop from mid-afternoon into this evening. Multiple areas of
   initiation are anticipated, but the most likely corridor for
   persistent supercells is from the Big Horn Basin into northwest
   SD/southwest ND.

   Large hail will likely be the primary risk during the late afternoon
   to early evening. Tornado potential should be maximized near the
   southwest ND/northwest SD border region just northeast of the lee
   cyclone where surface winds are backed. Consolidation into clusters
   or a broader MCS is probable as a moderate southerly low-level jet
   develops. This may yield a predominant risk for severe wind during
   the evening eastward along the ND/SD border region, with this threat
   likely waning overnight. 

   ...Mid-Atlantic States to Midwest...
   Scattered thunderstorms are expected during mid afternoon to early
   evening from NJ/PA westward across the Lower Great Lakes into IA.
   This activity should be focused near a pair of MCVs moving
   east-southeast from far southern Lake Ontario and northern Lake MI,
   along with the presence of a weak front/wind shift. Greater buoyancy
   should be displaced south/southwest from modestly enhanced mid-level
   flow to the north/northeast. As a result, storm organization should
   be limited to loosely organized multicells with effective shear
   generally less than 25 kt. Locally damaging winds will be the
   primary hazard. 

   ...Central/eastern Maine...
   Isolated thunderstorms have initiated within an environment
   characterized by an elongated hodograph amid strong deep-layer speed
   shear. However, weak mid-level lapse rates to the south of a
   vorticity maximum sliding southeast towards the Canadian Maritimes
   will be a limiting factor to more robust updraft strength. As such,
   locally damaging winds and marginally severe hail should be the most
   likely hazards. See MCD 1339 for additional short-term information.

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