RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Sat Jul 18 11:02:02 UTC 2026.
No Mesoscale Discussions are in effect as of Sat Jul 18 11:02:02 UTC 2026.
SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0202 AM CDT Sat Jul 18 2026
Valid 201200Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE UPPER MIDWEST/GREAT LAKES...
...SUMMARY...
Severe thunderstorms are possible across portions of the Upper
Midwest and Great Lakes vicinity on Monday. Swaths of damaging winds
will be the most likely hazard with this activity.
...Upper Midwest/Great Lakes vicinity...
An upper shortwave trough initially over the northern Plains will
deepen as it shifts east/southeast over the Great Lakes.
Northwesterly flow aloft will increase over the region as this
occurs. A surface low will deepen as it moves across southern
Manitoba and western Ontario toward the northern Great Lakes.
Meanwhile, a trailing cold front will sweep across the Upper
Midwest, becoming oriented from northern Lower MI southwestward
toward the Lower MO Valley by Tuesday morning.
A very moist airmass (70s dewpoints) will be in place ahead of the
cold front, fostering a corridor of strong to extreme instability
across parts of southeast MN into WI and portions of the Mid-MS
Valley. Supercell wind profiles are evident in forecast soundings,
though linear forcing along the front, and the progressive nature of
the upper trough, is likely to result in a bowing line of convection
moving across the region. While all severe hazards will be possible
given the favorable thermodynamic and kinematic environment, storm
mode will likely favor a predominant risk for swaths of damaging
winds. Eastward extent of severe potential is a bit uncertain as
some guidance maintains rather strong capping toward Lake MI.
Forecast trends will be monitored, and higher probabilities may be
needed in a subsequent outlook.
...North Carolina...
Broad upper troughing will persist across portions of the eastern
U.S. on Monday, and modest west/northwest flow aloft will overspread
the southern Mid-Atlantic vicinity. A stalled surface front across
northeast NC will move north through the morning, and a very moist
and unstable airmass will be in place. Convection developing within
low-level confluence south of the surface boundary may pose a risk
for wet microbursts given steep low-level lapse rates and high PW
values.
..Leitman.. 07/18/2026
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Day 4-8 Outlook
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 AM CDT Sat Jul 18 2026
Valid 211200Z - 261200Z
...DISCUSSION...
...Day 4-5/Tue-Wed -- Ohio Valley to Mid-Atlantic Vicinity...
An upper trough will pivot across the region on Tuesday and
Wednesday, bringing enhanced southerly flow aloft as a surface cold
front sweeps east/southeast through Wednesday night. Ahead of the
surface front, rich boundary layer moisture will be in place, and at
least moderate destabilization should occur. Convection could be
ongoing Tuesday morning across parts of IL/IN/Lower MI/western OH.
The extent of this activity is unclear and will depend on the
evolution of any potential MCS in the Day 3 period. Nevertheless,
the downstream airmass across parts of the Ohio Valley will become
favorable for scattered severe thunderstorms Tuesday afternoon and
evening, likely in the form of one or more line segments organizing
ahead of the advancing cold front. An additional area of severe
storms will be possible on Tuesday across the Mid-Atlantic within a
warm advection regime ahead of the approaching system over the Ohio
Valley. Some areas could see more than one round of severe
thunderstorms on Tuesday/Tuesday night.
By Wednesday, the severe risk should spread east from the
Mid-Atlantic into the Carolinas as the upper trough and surface cold
front continue to shift east. It is uncertain how far north the
severe risk may extend and probabilities may eventually need to be
included across parts of the Northeast/New England. Where storms do
form, damaging winds will be possible until the cold front moves
offshore Wednesday evening/night.
...Days 6-8/Thu-Sat...
Upper troughing will persist across the eastern U.S. through the end
of the forecast period, but deep-layer flow will weaken. High
pressure in the wake of the cold frontal passage will preclude
severe potential across the Ohio Valley into the Mid-Atlantic and
Northeast Thursday through Saturday.
Across the Plains and western U.S., a strong upper anticyclone will
park over the southern Plains, with an amplified upper ridge
building into the northern Rockies. Some thunderstorm potential
could develop across parts of the Plains as low-level moisture
increases beneath the ridge. However, severe potential is uncertain
as any potential would be driven by mesoscale features not well
defined at this time frame, and as the upper ridge suppresses any
large-scale support for organized severe thunderstorms.
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