SPC AC 031958

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0258 PM CDT Wed Jul 03 2019

   Valid 032000Z - 041200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF WY
   INTO THE NORTHERN PLAINS...

   ...SUMMARY...
   The most likely region for severe thunderstorms today remains across
   portions of Wyoming into the northern Great Plains. A couple
   tornadoes, large hail, and severe wind gusts will be possible, with
   the peak threat from late this afternoon to evening.

   ...20Z Update...
   Only very minor changes have been made to the Slight Risk across
   parts of the northern/central Rockies into the northern Plains.
   Convective inhibition continues to erode to the south of a front
   across these regions. Thunderstorms forming over the higher terrain
   of WY are expected to develop northeastward into the NE Panhandle,
   SD, and eventually parts of ND later this afternoon and evening.
   Large hail should be the main threat initially, with a gradual
   transition to a severe wind threat probable with eastward extent
   across the Dakotas. A tornado or two may also occur across parts of
   western SD and vicinity along the surface front.

   There is still not enough confidence in a possible corridor of
   damaging winds across western/central SD later this evening to
   include higher severe wind probabilities. For more information on
   the short-term severe threat across this region, see recently issued
   Mesoscale Discussion 1353 and Severe Thunderstorm Watch 479.

   Elsewhere, parts of northern/central IL/IN/OH have been removed from
   Marginal Risk where additional strong thunderstorms to the north of
   a weak surface boundary appear unlikely through this evening.

   ..Gleason.. 07/03/2019

   .PREV DISCUSSION... /ISSUED 1127 AM CDT Wed Jul 03 2019/

   ...Northern Rockies/Plains...
   Considered an upgrade to Enhanced Slight Risk across parts of the
   Dakotas but confidence is currently too low to identify the most
   probable severe wind corridor.

   A pair of primary shortwave impulses are evident in water vapor
   imagery, the lead one ejecting into western MT and a lagging one
   over southwest OR. These features will translate gradually east
   through the period, fostering weak mid-level height falls over
   mainly the northern Rockies and adjacent High Plains. Stronger
   mid-level southwesterlies will accompany the lead impulse with a
   belt of 40-55 kt 500-mb flow centered on the Yellowstone vicinity
   into western ND at peak heating. Lee cyclogenesis will occur across
   southeast WY with a slow-moving front extending northeast across the
   Dakotas.

   Thunderstorms are already ongoing in association with the lead
   impulse across southwest MT. Despite this activity occurring within
   50s surface temperatures and pervasive cloudiness downstream
   limiting boundary-layer heating, the cold pocket of mid-level
   temperatures will support sufficiently steep lapse rates amid weak
   buoyancy. This could yield a swath of marginally severe hail into
   the afternoon. Towards mid-late afternoon, more numerous
   thunderstorms should develop in the mountains surrounding the
   Bighorn Basin, near the surface cyclone in southeast WY, over the
   Black Hills, and along the front in central ND. The more long-lived
   supercell corridor should exist across the northeast WY to western
   SD vicinity as it lies on the western plume of moderate to large
   buoyancy with low-level SRH enhanced on the cool side of the front.
   Large hail and a couple tornadic supercells are possible. 

   Although CAMs are rather varied, there is signal for upscale growth
   and potential development of one or more MCS/s eastward across
   mainly SD and eastern ND this evening. This will be highly dependent
   on storm-scale/supercell interactions, especially with southeast
   extent given the displacement of stronger mid-level flow to the cool
   side of the front and the southerly low-level jet well south across
   the central Great Plains. However, encroachment on a plume of
   2500-3500 J/kg MLCAPE may support at least isolated severe wind
   gusts persisting into the early morning.

   ...Coastal Carolinas...
   A modest belt of mid/upper-level westerlies will overlap the sea
   breeze, yielding potential for multicell clustering. Larger buoyancy
   prevails along the immediate coast, especially compared to areas
   farther inland to the north/west that are east of the Appalachians,
   as robust heating has occurred amid the presence of mid to upper 70s
   surface dew points. While weak lower-level flow should limit greater
   organization, locally strong wind gusts and marginally severe hail
   will be possible for a few hours during mid-late afternoon.

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