LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Sun Jul 27 2025
Valid 271200Z - 281200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER MISSISSIPPI VALLEY AND WESTERN GREAT LAKES...
...SUMMARY...
Severe thunderstorms will be possible this afternoon and evening
from parts of the upper Mississippi Valley into the western Great
Lakes. Marginally severe storms will also be possible in parts of
the northern Plains, central Appalachians, Mid-Atlantic and eastern
North Carolina.
...Upper Mississippi Valley/Western Great Lakes/Northern Plains...
A shortwave mid-level trough will move eastward into the western
Great Lakes today, as a ridge moves into the northern Plains. At the
surface, a cold front will advance southeastward across the northern
Plains, as a moist and unstable airmass remains over much of the
upper Mississippi Valley. As surface temperatures warm during the
day, thunderstorm development will be likely from the front in
north-central Minnesota eastward to near the tip of Lake Superior.
Convective coverage is forecast to expand in coverage during the
late afternoon as a line segment organizes and moves eastward across
the region.
Ahead of the front, surface dewpoints are expected to be mostly in
the 70s F. This will contribute to the development of strong
instability by afternoon. RAP forecast soundings by 21Z near the
instability axis have MLCAPE in the 2500 to 3500 J/kg range. In
addition, 0-6 km shear is forecast to be around 30 knots, which
should be sufficient for isolated supercell development. Large hail
will be possible with any cell that can become locally intense.
Although supercells will be possible, the most common storm mode
should be multicellular. Some model forecasts suggest that a broken
line segment will develop and move from central and eastern
Minnesota into northern Wisconsin during the mid to late afternoon.
These storms should have wind-damage potential. Additional
development should occur as the low-level jet gradually ramps up,
further to the southwest across parts of far eastern South Dakota
and south-central Minnesota. Isolated large hail and wind damage may
occur with these storms as well.
Further west into parts of northern North Dakota and northern
Montana, moderate instability is expected to develop in some areas
by late afternoon and early evening. Isolated to scattered
thunderstorms may develop across parts of this post-frontal airmass.
RAP forecast soundings by late afternoon from northeast Montana into
northwest North Dakota suggest that moderate deep-layer shear and
steep mid-level lapse rates will be in place. This should support an
isolated severe threat. However, the severe threat should be
marginal, mainly due to limited large-scale ascent.
...Central Appalachians/Mid-Atlantic/Eastern North Carolina...
Northwest mid-level flow will be in place today across much of the
northeastern U.S., as a subtle shortwave trough moves southeastward
across the region. A north-to-south axis of moisture and instability
is forecast to be in place by afternoon from eastern North Carolina
into the Mid-Atlantic. Isolated to scattered thunderstorms are
expected to develop in the afternoon near the instability axis, and
in the higher terrain of the central Appalachians. RAP forecast
soundings late this afternoon near the instability axis have MLCAPE
peaking around 3000 J/kg, with steep low-level lapse rates and
surface dewpoints in the upper 70s F. This environment should
support a marginal wind-damage threat with the stronger multicells.
..Broyles/Squitieri.. 07/27/2025
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