SPC AC 111730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Sun Jun 11 2017

   Valid 121200Z - 131200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN
   WYOMING...WESTERN NEBRASKA...WESTERN SOUTH DAKOTA AND SOUTHEAST
   MONTANA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
   THE CENTRAL AND NORTHERN HIGH PLAINS INTO THE NORTHERN ROCKIES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   NORTHERN ROCKIES THROUGH THE UPPER MISSISSIPPI VALLEY AND GREAT
   LAKES...

   ...SUMMARY...
   Severe thunderstorms are expected from the vicinity of the Laramie
   and Big Horn mountains into the Black Hills, and surrounding areas
   of the northern Plains, Monday afternoon into Monday night.
   Significant severe weather including very large hail, tornadoes and
   damaging wind appear likely over portions of this region.

   ...Synopsis...

   Upper low currently centered over northern CA will move through the
   great basin region Monday and eventually into the central and
   northern Rockies Monday night. An upper jet max will rotate through
   the base of this feature and into parts of CO and WY Monday
   afternoon and evening. At the surface, trailing portion of cold
   front that will move into the northern Great Lakes region will stall
   from NE to northern CO before returning north as a warm front in
   response to cyclogenesis over northern CO and southeast WY. Dryline
   will extend from the southern and central high Plains northwestward
   to the surface low near the CO/southeast WY border by mid day, and
   this boundary will continue to mix northeast during the afternoon.

   ...Central high Plains through northern Rockies...

   Southwesterly flow aloft will maintain plume of steep 7.5 - 8C/km
   mid-level lapse rates over the central high plains into a portion of
   the northern Rocky Mountain region. Evolving easterly low-level
   trajectories in vicinity of warm/quasistationary front will advect
   mid-upper 50s F dewpoints into southeast WY and northeast CO with
   60s farther east into NE. These processes along with diabatic
   warming during the afternoon will result in moderate-strong
   instability with MLCAPE from 1500-2500 J/kg. Current indications are
   that storms should develop within zone of orographic forcing over
   the mountains of WY into northern CO supported by increasing upper
   divergence and deep layer forcing for ascent accompanying the upper
   jet streak rounding base of the trough. Activity will spread
   northeast above the destabilizing boundary layer. Mid-upper level
   south southwest winds will increase with approach of the upper jet
   which, in conjunction with strongly veering low-level winds and
   large hodographs near and north of the warm front, will support a
   threat for supercells with low-level mesocyclones capable of
   producing very large hail and tornadoes. Initial storms will likely
   be discrete for a few hours, but activity should eventually grow
   upscale during the evening as the low-level jet strengthens above
   easterly near-surface winds north of the warm front, likely
   supporting a forward propagating MCS with an increasing threat for
   damaging wind. 

   ...Upper Mississippi Valley/adjacent Great Lakes...

   Severe weather potential remains conditional in this region given
   uncertain initiation of storms and potential storm coverage, in the
   presence of generally weak shear but moderate to strong instability.
    Forcing for storm development appears to largely hinge on lift
   driven by lower/mid tropospheric warm advection on the northern
   periphery of the elevated mixed layer plume, which may remain
   stalled across parts of the Upper Midwest, while advecting northward
   across the northern Plains toward the international border.

   ..Dial.. 06/11/2017

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z