SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1238 AM CDT Tue Sep 20 2022
Valid 201200Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
GREAT LAKES REGION...
...SUMMARY...
Isolated severe thunderstorms are expected across parts of the upper
Great Lakes late Tuesday afternoon/evening. Hail is the primary risk
with this activity.
...Upper Great Lakes...
Pronounced upper trough is currently located over SK/AB. This
feature is forecast to dig southeast into the upper Great Lakes
region by the end of the period as 90kt 500mb speed max translates
across northern MN toward northwestern WI. As the short wave
advances downstream, surface pressures will rise across the southern
Canadian prairies/northern Great Plains. This will force a cold
front into the upper MS Valley by late afternoon, arcing from the
arrowhead of MN-southeast SD by 21/00z. Additionally, early-day
convection is expected across portions of WI/lower MI which should
enhance a weak boundary draped across southern WI into southeast MN.
Strongest boundary-layer heating is forecast ahead of the cold front
across NE into extreme south-central MN. While modest heating is
expected ahead of the cold front near the international border,
surface temperatures may struggle to hit convective temperatures.
Even so, minimal inhibition will be noted along this advancing wind
shift by late afternoon and frontal ascent, aided by large-scale
height falls ahead of the upper trough, suggest isolated convection
should evolve along/just post frontal. The primary corridor for
initiation appears to be from western Lake Superior region into
western WI. Forecast soundings favor supercells, and while this
activity may be slightly elevated, ample buoyancy along with steep
lapse rates suggest robust updrafts are possible. Large hail is the
greatest risk with supercells that evolve across this region during
the early evening. Strengthening height falls during the latter half
of the period may allow remnants of this activity to spread toward
lower MI late; however, convection should weaken downstream where
weaker buoyancy is expected.
..Darrow/Weinman.. 09/20/2022
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