126
ACUS01 KWNS 150601
SWODY1
SPC AC 150600

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Thu May 15 2025

Valid 151200Z - 161200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
EASTERN MINNESOTA...WISCONSIN...NORTHEAST ILLINOIS...NORTHERN
INDIANA...SOUTHWEST AND SOUTHERN MICHIGAN...AND FAR NORTHWEST
OHIO...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MID TO UPPER MISSISSIPPI VALLEY...GREAT LAKES...OHIO VALLEY AND
MID-ATLANTIC...

...SUMMARY...
Severe thunderstorms are expected across parts of the upper
Mississippi River Valley and Great Lakes this afternoon and evening.
Hailstones greater than 2 inches will be possible, along with
tornadoes with a few that could be strong. Scattered wind damage
will be likely, with wind gusts over 75 mph over parts of Lower
Michigan and northern Indiana. Isolated severe thunderstorms are
also expected through the lower Ohio River Valley, Ozarks and in
parts of the Mid-Atlantic.

...Mid to Upper Mississippi Valley/Great Lakes/Ohio Valley...
A negatively-tilted mid-level trough will move northeastward into
the Upper Midwest today, as an associated jet streak translates
eastward into the Ozarks. A secondary jet streak will move
northeastward into the mid Missouri Valley. Strong large-scale
ascent will overspread a broad moist sector from the Great Lakes
into the Ohio Valley, resulting in a widespread severe weather event
today.

At the surface, a low will consolidate and move northward across the
eastern Dakotas. A well defined warm front will advance northward
into the Wisconsin, as a cold front moves eastward into the mid to
upper Mississippi Valley. Ahead of the front, surface dewpoints from
the mid 60s to the lower 70s F will result in moderate instability
over much of the moist sector. Thunderstorms are first expected to
initiate near the mid-level low over the upper Mississippi Valley,
with storms developing south-southeastward along and ahead of the
front during the afternoon.

Indications suggest that the storms will remain somewhat spaced out,
at least early in the event. The discrete nature of the convection,
combined with moderate deep-layer shear, will be favorable for
supercell development. A broken line of severe storms is expected to
move east-northeastward into the vicinities of Milwaukee and Chicago
late this afternoon. RAP forecast soundings at 21Z along the western
shore of Lake Michigan have MLCAPE near 2000 J/kg, with 0-6 km shear
of 35 to 40 knots, and 700-500 mb lapse rates near 7.5 C/km. This
will be favorable for large hail and wind damage associated with
supercells. The more intense supercells may produce hailstones
greater than 2 inches in diameter. In addition, 0-3 km
storm-relative helicity in the 250 to 300 m2/s2 will also support
tornadoes, with the threat becoming maximized as supercells mature.
A few strong tornadoes appear likely.

Severe threat coverage will likely be maintained as a broken line
segment gradually organizes. A transition to linear mode appears
likely by early evening. Supercells and rotating elements within the
line should be capable of producing tornadoes. Wind damage will also
be likely along the leading edge of the line, with gusts over 75 mph
possible from western Lower Michigan southward into northern
Indiana. A potential for hailstones greater than 2 inches in
diameter will continue during the early evening with supercells
embedded within the line.

Further south into the lower Ohio Valley, storm coverage will be a
bit more isolated. However, cells that can develop within the
strongly unstable airmass will likely become supercells with large
hail and severe gusts. A tornado threat is also expected. It appears
that a corridor of greater severe threat will develop somewhere near
the Ohio River during the late afternoon, which could be dependent
upon the distribution and magnitude of instability.

...Ozarks/Ark-La-Tex...
Southwest mid-level flow will be in place today across the Ozarks
and Ark-La-Tex, as a jet streak moves eastward into the region. A
moist airmass will be in place to the southeast of the jet, where
surface dewpoints will be in the upper 60s and lower 70s F. By
afternoon, much of this airmass will be moderately unstable.
However, large-scale ascent to the south of the jet is forecast to
remain relatively weak, which should keep convective development
isolated. Any cell that can initiate despite a capping inversion
could become severe and have a large hail and wind-damage threat.
The threat could persist from late afternoon into the early evening.


....Central Appalachians/Mid-Atlantic...
A mid-level ridge will move eastward into the central Appalachians
today, as northwesterly flow remains to the east of the Appalachian
crest. At the surface, a moist airmass will be in place along much
of the southern and central Atlantic Seaboard. Surface dewpoints in
the 60s F will likely result in moderate instability by afternoon.
Although large-scale ascent will be weak, topographic forcing and
increasing low-level convergence could aid convective initiation as
surface temperatures warm up. Short-term model solutions suggest the
greatest convective potential will be across eastern Virginia, where
low-level flow is forecast to increase during the day. This,
combined with moderate deep-layer shear and steep low-level lapse
rates, may be enough for an isolated severe threat. Severe wind
gusts and large hail will be possible with supercells or short
intense line segments.

..Broyles/Lyons.. 05/15/2025

$$