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ACUS01 KWNS 191648
SWODY1
SPC AC 191647

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1147 AM CDT Fri Jul 19 2019

Valid 191630Z - 201200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS
EAST-CENTRAL MINNESOTA AND NORTHERN WISCONSIN...

...SUMMARY...
A regional outbreak of severe thunderstorms with the possibility of
strong tornadoes and widespread significant wind damage is expected
from central Minnesota across northern Wisconsin during the mid/late
afternoon into tonight.

...Upper Midwest/Great Lakes...
A regional outbreak of severe thunderstorms is expected later this
afternoon into tonight. That said, some specific uncertainties
remain with the timing details/exact sub-regional corridor of peak
severe-weather risk given capping/warm temperatures aloft and
uncertainty with the decay of the cloud shield from the earlier MCS
across South Dakota.

A very strong summertime belt of westerlies exists across the
northern tier of the CONUS, with 50-100 kt westerlies noted between
500/250 MB in 12Z upper-air data spanning Montana to the
Dakotas/Minnesota. Where storms develop/increase later today, this
very strong belt of winds aloft will be influential in storm
organization including supercells and potential evolution of a
fast-moving MCS (possible if not likely derecho) later
today/tonight.

Consult Mesoscale Discussion 1523 regarding midday details across
western Minnesota. Additional surface-based thunderstorm development
may emanate from the ascent/differential heating related to the MCS
remnants, focusing downstream surface-based severe potential across
central Minnesota. An extremely unstable air mass (MLCAPE >4000
J/kg) will continue to become established from southeast Southeast
South Dakota through central/southern Wisconsin as the elevated
mixed-layer overspreads surface dew points rising into the mid to
upper 70s. A surface cyclone over central South Dakotas should track
towards the Twin Cities through early evening. Strong low-level
convergence near/northeast of this cyclone along the warm front
should sustain surface-based storm development across central into
east-central Minnesota.

Intense supercells are likely to develop rapidly, with an attendant
threat for all severe hazards including the possibility of a strong
tornado or two amid 50-60 kt effective shear and 0-3 km SRH >300
m2/s2. The very warm/moist thermodynamic profiles will also support
generation of strong cold pools which should eventually yield a
bowing, forward-propagating MCS across northern Wisconsin into parts
of northern Lower and Upper Michigan. Strength of the vertical shear
suggests the potential for intense bowing segments capable of
yielding a derecho with significant/widespread severe wind gusts.

...Lower Great Lakes/Northeast States...
Have upgraded parts of the region for thunderstorm-wind related
potential this afternoon into evening. This will be related to the
possible east-southeastward persistence of a complex of storms
across Ontario and additional scattered development that is expected
in the lee of the Lower Great Lakes. The ambient air mass will be
moderately to strongly unstable but the region will generally be
south of the stronger westerlies aloft. The overall expectation is
for predominantly multicellular, outflow-dominant storms capable of
isolated damaging wind gusts this afternoon and evening.

...South Dakota tonight...
Another round of 700-mb warm/moist advection will occur tonight
within a tight baroclinic zone well north of a surface front arcing
across Nebraska into northeast Wyoming. Large elevated buoyancy and
strong effective shear will support a risk for isolated large hail.
While storms will generally tend to be elevated, there may be some
wind damage potential if upscale quasi-linear growth occurs late
tonight as storms progress east-southeastward across South Dakota.

..Guyer/Wendt.. 07/19/2019

$$


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