Severe Storm Outlook Narrative (AC)
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
000
ACUS02 KWNS 201656
SWODY2
SPC AC 201655

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1155 AM CDT Wed Sep 20 2017

Valid 211200Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN
DAKOTAS INTO THE UPPER GREAT LAKES...

...SUMMARY...
Hail-producing storms are possible from the eastern Dakotas into the
U.P. of Michigan Thursday night.

...Discussion...

Pronounced upper trough will migrate into the Great Basin by the end
of the day2 period as strongest 500mb flow translates into the
central Rockies. Ahead of this feature, mid-level heights will rise
across the north-central US and a lee surface cyclone should evolve
over the high Plains which will shift into SD during the overnight
hours. Prior to this lee cyclone development, surface front should
stall across southern WI/IA region then lift north during the latter
half of the period in response the approaching upper trough. The
lack of large-scale forcing for ascent along this front, combined
with height rises, suggest deep convection will struggle to develop
much of the day. However, moisture advection in response to
strengthening LLJ during the overnight hours is expected to aid
destabilization atop retreating continental air mass over the upper
MS Valley. Forecast soundings suggest substantial elevated
instability will evolve from the eastern Dakotas into the upper
Great Lakes region where MUCAPE is forecast in excess of 3000 J/kg
along the cool side of the boundary. Latest guidance suggest
elevated thunderstorms will evolve along a corridor from the eastern
Dakotas toward Lake Superior after 06z. Large hail could be noted
with this activity. At this time will maintain 5% severe
probabilities due to aforementioned height rises but there is some
concern that a corridor of elevated thunderstorms could evolve such
that higher severe probs may be warranted after dark.

..Darrow.. 09/20/2017

$$



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.