SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1149 PM CDT Mon Jul 21 2025
Valid 231200Z - 241200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WEDNESDAY INTO
WEDNESDAY NIGHT ACROSS PARTS OF CENTRAL AND NORTHEASTERN
NEBRASKA...SOUTHEASTERN SOUTH DAKOTA...NORTHEASTERN IOWA...SOUTHERN
MINNESOTA...NORTHERN WISCONSIN...UPPER MICHIGAN...
...SUMMARY...
Organizing clusters of storms posing a risk for severe wind are
possible across parts of the middle Missouri Valley and Upper
Midwest into adjacent portions of the Great Lakes region Wednesday
through Wednesday night.
...Discussion...
Models continue to indicate further suppression of the northeastern
Pacific mid-level ridging, with flow becoming more zonal and
progressive across the British Columbia coast into the Canadian
Prairies during this period. Downstream, it still appears that
mid/upper flow will continue to intensify in a belt across Ontario
through Quebec, between a significant trough and cyclone slowly
migrating eastward across Hudson Bay and prominent ridging initially
centered over the Ohio Valley. A cold front trailing the cyclone is
still likely to advance more rapidly southward across the Great
Plains, to the lee of the Rockies, than across the Upper Midwest and
adjacent Great Lakes region.
This general evolution has been forecast for several days, but
spread has been evident within and among the various model output
concerning the synoptic and, particularly, sub-synoptic
developments, which persists in latest model runs. Among the
details which remain characterized by sizable spread, the cold
frontal progression through the Great Plains/mid Missouri Valley
vicinity, the strength of a short wave perturbation progressing out
of the Pacific Northwest through the central Canadian/U.S. border
vicinity, and weak mid/upper perturbations migrating around the
southern and northwestern periphery of the interior U.S. ridge,
across the Gulf coast and southern Great Plains toward upper
Mississippi Valley. These and other smaller-scale perturbations,
with low predictability at this time frame, will considerably impact
the convective potential for Wednesday through Wednesday night.
...Mid Missouri Valley into Upper Midwest/Great Lakes...
While it still appears that the southern fringe of the stronger
mid/upper westerlies will not extend south of a corridor from
southeastern Minnesota through northern Wisconsin and Upper
Michigan, models now generally indicate a belt of moderate
south-southwest flow (20-40 kt in the 850-700 mb layer) in the
lower/mid-levels will develop across the central Great Plains into
the Upper Midwest, ahead of the weak perturbation migrating around
the western periphery of the mid-level ridge.
Beneath modestly steep lapse rates, but with generally warm
profiles, it now appears increasingly probable that seasonably high
boundary-layer moisture content, supportive of large mixed-layer
CAPE, will extend along the frontal zone from the Upper
Midwest/Great Lakes as far southwest as central/northeastern
Nebraska by late afternoon. Coupled with the strength of the
lower/mid-tropospheric flow, it appears probable that this
environment will become supportive of one or two organizing
thunderstorm clusters with potential to produce swaths of strong to
severe wind gusts. However, based on late model output, including
available convection allowing guidance, the potential evolution
Wednesday through Wednesday night remains rather uncertain at this
time.
...Northern Rockies into Front Range...
In the presence of steep lapse rates, moistening easterly to
southeasterly near-surface flow, beneath modest westerly flow aloft,
may contribute to sufficient destabilization and shear to support
widely scattered strong to severe storms. This may include evolving
supercells near/just east of the higher terrain late Wednesday
afternoon and evening.
..Kerr.. 07/22/2025
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