Milwaukee, WI...Minneapolis, MN...St. Paul, MN...Madison, WI...Sioux Falls, SD...
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
...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
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.
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
...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.
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