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ACUS01 KWNS 180601
SWODY1
SPC AC 180600

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Thu Jul 18 2019

Valid 181200Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
MIDWEST...

...SUMMARY...
Areas of severe storms are possible across the Upper Midwest on
Thursday.

...Synopsis...
Upper ridging and weak flow aloft will remain in place across the
central and southern CONUS while enhanced westerly flow aloft
extends from the Pacific Northwest through the Upper Great Lakes. A
convectively induced shortwave will likely move across the Upper
Great Lakes early Thursday, moving into eastern Ontario by Thursday
evening. A second shortwave trough (and associated speed max) is
expected to move across the northern Rockies Thursday evening.

At the surface, broad area of low pressure currently in place across
the central and northern Plains expected to remain largely in place
while lee troughing across the High Plains deepens. Southern portion
of a cold front associated with a low moving across the Canadian
Prairie provinces will move across the northern Plains Thursday
evening.

...Upper Midwest...Upper Great Lakes...
Showers and thunderstorms will likely be ongoing across the region
early Thursday morning. Most of these storms are expected to weaken
as the low-level jet loses strengthen and they drift northeastward
into a more stable air mass. The only exception is storms along the
southern periphery of the anticipated storm cluster. In this area,
the low-level jet will likely remain stronger longer, helping to
maintain storm intensity as warm, moist, and unstable air is
continually advected into the storms. The development of a
forward-propagating convective line may occur, with the resulting
line moving into northern IL and northern IN. Confidence in the
development of a convective line is currently too low to introduce
more than 5% probabilities but higher probabilities may be needed in
subsequent outlooks.

During the late afternoon, scattered, predominately cellular
thunderstorms are possible along and ahead of the cold front moving
through the northern Plains and into the Upper Midwest. Despite
dewpoints in the mid 60s, warm mid-level temperatures and only weak
surface convergence suggest limited storm coverage. Long hodographs
support rotating updrafts with any storms that do form. Primary
severe threat will be strong wind gust but large hail and a tornado
or two are also possible.

Thunderstorms are also possible across southern MN and
central/southern WI Thursday evening. Residual outflow from
antecedent storms combined with a strengthening low-level jet and
the approaching front is expected to result in thunderstorm
initiation. Dewpoints in this region are expected to be in the low
to mid 70s with mid-level lapse rates likely around 7.5 deg C per
km. As a result, extreme buoyancy will be in place with MLCAPE over
4000 J/kg. Given the onset of nocturnal cooling, these storms may
have a relatively brief window to remain surface-based. Even so, the
strong instability coupled with modest vertical shear supports the
potential for severe thunderstorms. Primary severe threat is
damaging wind gusts but large hail and a tornado or two are also
possible.

..Mosier/Bentley.. 07/18/2019

$$


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