SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Wed Aug 24 2022
Valid 242000Z - 251200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
NORTHERN ROCKIES TO UPPER THE MISSISSIPPI VALLEY...
...SUMMARY...
Marginally severe gusts and/or hail will be possible in a corridor
from portions of the northern Rockies to the upper Mississippi
Valley.
...Discussion...
No change was made to the previous convective outlook.
...Lower CO River Valley and for northeast NV and adjacent portions
of northwest UT...
The 18z 1Y7 raob in southwest AZ showed a 2 inch PW with weak flow
below 500 mb. A few strong thunderstorms with gusty winds are
probable in the lower CO Valley and northeast NV/northwest UT.
Evolution of yet-to-be generated outflow casts large enough
uncertainty to preclude the introduction of low-severe probabilities
at this time.
..Smith.. 08/24/2022
.PREV DISCUSSION... /ISSUED 1121 AM CDT Wed Aug 24 2022/
...Northern Rockies to upper Mississippi Valley...
Modest west-northwest mid-level flow will prevail from the Northern
Rockies into the upper Great Lakes through tonight. An upper low
over WA will drift east, while a low-amplitude impulse over western
MN moves slowly southeast. A surface front, extending from the MI
Upper Peninsula west/southwest through western NE and southern MT,
will serve as a focus for isolated severe potential as thunderstorms
develop/intensify this afternoon. Two areas with potentially greater
thunderstorm coverage remain evident, over portions of southeast
MN/northern IA/southern WI associated with a weak surface low along
the front over southern MN, and over western MT in association with
the eastward-migrating upper low.
Relatively greater boundary-layer moisture exists over IA/southern
MN late this morning (surface dew points mid 60s), and this will
contribute to pockets of moderate MLCAPE where heating can be
maximized. Generally weak low/mid-level wind fields will result in
effective shear below 30 kts, though this may support organized
multicell structures capable of isolated damaging gusts and hail
late this afternoon through early evening.
Across western MT, steeper mid-level lapse rates will contribute
moderate buoyancy, and effective shear values will average 30-40
kts. Scattered thunderstorms should develop this afternoon, aided by
post-frontal upslope flow and ascent with the approaching upper low.
A mix of multicell and transient supercell storm modes is possible
with a risk for isolated severe wind and hail with the strongest
storms. A focused Slight Risk was considered over portions of
western MT, however with existing cloud cover some uncertainty
remains regarding the degree of destabilization and spatial extent
of any greater severe threat.
Elsewhere along the front, storm coverage is expected to be more
isolated overall, though with perhaps slightly greater coverage in
the upslope region of the Black Hills in western SD. A well-mixed
boundary layer and marginal low-level moisture will support at least
some risk for strong wind gusts.
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