SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1234 PM CDT Fri Sep 16 2022
Valid 171200Z - 181200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MINNESOTA/IOWA AREA...
...SUMMARY...
Isolated severe thunderstorms -- and local/all-hazards severe
potential -- are expected Saturday from parts of the Upper
Mississippi Valley area/Upper Midwest into/across portions of the
Mid Missouri Valley.
...Synopsis...
An initially low-amplitude upper flow pattern over the U.S. will
gradually amplify, especially over the West. This amplification
will result from a broad low from British Columbia to just off the
Pacific Northwest Coast early in the day, that is expected to
strengthen/consolidate as it shifts southward to just off the
northern California coast late.
As this occurs, ridging will begin to expand across the
south-central U.S., while a belt of fast southwesterly flow in
between the two features persists from the Intermountain West to the
Upper Great Lakes.
At the surface, the primary feature of interest will be a weak low
-- forecast to evolve over the eastern South Dakota/southwestern
Minnesota border area during the afternoon. A weak cool front
should extend south-southwestward across eastern Nebraska and into
Kansas, while the warm front extends east-northeastward across
northern Minnesota. The main severe potential Saturday should
reside in the vicinity of the warm sector of this system.
...Minnesota to southwestern Wisconsin/Iowa, and southwestward
across northeastern Kansas...
Though hindered in some areas by ongoing/remnant clouds/convection
early in the period, daytime heating and low-level moist advection
within the southerly flow regime will result in moderate afternoon
airmass destabilization from the Upper Midwest into Kansas. As a
short-wave trough crosses the Dakotas early and eventually
approaches Minnesota, ascent -- focused near a weak low progged to
evolve near the South Dakota/Minnesota border -- will likely result
in isolated storm development by late afternoon.
Farther south, focus for convective initiation appears more
nebulous, without a clear low-level focusing mechanism. Still,
low-level warm advection across this region should result in
isolated to scattered convective development -- initially during the
afternoon, with a second round of storms possible as a southerly
low-level jet intensifies overnight.
With 35 to 40 kt west-southwesterly mid-level flow spreading across
the area with time, atop low-level southerlies, a few of the
stronger storms will likely acquire rotation -- posing risk for hail
and/or locally damaging wind gusts. A tornado or two may also occur
-- with a favored area possibly over central/northern Minnesota near
the anticipated low/warm frontal position. Storms will likely
continue -- especially across the Iowa vicinity -- overnight, aided
by persistent low-level warm advection, though any lingering severe
potential should wane gradually through late evening.
..Goss.. 09/16/2022
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