LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0101 AM CDT Wed Jul 26 2023
Valid 261200Z - 271200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE GREAT LAKES...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL PLAINS...
...SUMMARY...
Severe thunderstorms associated with wind damage and isolated large
hail will be possible today in parts of the southern Great Lakes
region. A severe threat is also expected in parts of the central
Plains.
...Southern Great Lakes...
A large mid-level anticyclone will remain across much of the
southwestern and south-central U.S. today. To the northeast of this
feature, a shortwave trough will move eastward across the
north-central U.S. Ahead of the shortwave, a complex of
thunderstorms will likely be ongoing at the start of the period over
the upper Mississippi Valley. A moist airmass with surface dewpoints
in the 70s F will be in place across parts of the upper Mississippi
Valley eastward into the Great Lakes. As surface temperatures warm,
strong instability will likely develop from northern Illinois
eastward into lower Michigan. The complex of storms is forecast to
move east-southeastward into the stronger instability during the
late morning and early afternoon. A linear MCS is expected to
develop and move through the southern Great Lakes region this
afternoon.
A mid-level speed enhancement, associated with the shortwave trough,
will move east-southeastward into the Great Lakes this afternoon.
This feature will help to create moderate deep-layer shear across
much of the region, making conditions favorable for severe storms.
RAP forecast soundings in southwest Lower Michigan at 21Z have
MLCAPE near 3000 J/kg, 0-6km shear around 35 knots, and 0-3 km lapse
rates approaching 7 C/km. This should be favorable for wind damage
along the leading edge of the convective complex. The greatest
wind-damage threat will be associated with bowing line segments. In
addition, the wind profile will support supercell development with
storms that remain discrete. A large-hail threat will be possible
with supercells. Also, forecast soundings have 0-3 km storm-relative
helicity reaching 250 to 300 m2/s2 in parts of lower Michigan by
late afternoon. This suggests that a tornado threat may develop. The
MCS is expected to eventually outrun the stronger instability,
making the severe threat more isolated by early evening.
...Central and Northern Plains...
A mid-level anticyclone will remain in place across the Desert
Southwest and southern Plains today. A shortwave trough to the north
of the anticyclone will move eastward into the central High Plains
this afternoon. At the surface, upslope flow is forecast across
parts of western Kansas and central Nebraska, where surface
dewpoints are expected to be in the 50s F. As surface temperatures
warm ahead of the shortwave trough, an axis of moderate instability
is forecast to develop across far southern Nebraska. Thunderstorms
will likely initiate along the western edge of the stronger
instability, and move eastward across the central Plains this
afternoon. RAP forecast soundings along the instability axis in
south-central Nebraska have MLCAPE near 2000 J/kg, 0-6 km shear
around 40 knots, and low to mid-level lapse rates near 8.5 C/km.
This environment will be favorable for damaging wind gusts
associated with high-based short multicell line segments. In
addition, high-based supercells with isolated large hail will also
be possible.
Further to the north across the northern Plains, an axis of
instability is forecast to develop ahead of a cold front moving
through the western Dakotas. Along the instability axis, MLCAPE in
the 500 to 1000 J/kg combined with moderate deep-layer shear and
steep lapse rates may be enough for a marginal severe threat in the
afternoon.
..Broyles/Squitieri.. 07/26/2023
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