RSS Mesoscale Discussions from Storm Prediction Center
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0305 PM CDT Mon May 18 2026
Valid 182000Z - 191200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
CENTRAL AND NORTHEASTERN KANSAS...FAR SOUTHEASTERN
NEBRASKA...NORTHWESTERN MISSOURI...AND FAR SOUTHWESTERN IOWA....
...SUMMARY...
Numerous severe thunderstorms are expected this afternoon and
evening across the south-central Plains and mid Missouri Valley.
Supercells capable of producing very large to giant hail and
multiple strong to intense tornadoes remain likely from central
Kansas and southeast Nebraska into Iowa and northwest Missouri.
...20z Update Midwest Lower Great Lakes...
An expansive MCS remains ongoing over portions of the lower Great
Lakes this afternoon. The environment ahead of the complex is
unstable, but with gradually decreasing moisture/buoyancy farther
east. An isolated severe risk likely exists ahead of the line across
OH and lower MI through this evening.
A large cold pool behind the complex has overturned the air mass
across much of northern IL, southern WI and eastern IA. This should
greatly limit air mass recovery this afternoon and evening.
Additional convection originating from the central Plains and mid MO
valley may continue eastward, but is forecasted to weaken as it
encounters the cooler air mass tonight. Isolated storms, likely
elevated, could persist with a risk for hail, but the severe
potential has decreased such that, probabilities were lowered.
...Central Plains and Mid MO Valley...
Several supercells and organized clusters have emerged across parts
of KS and southern NE. A very unstable and strongly sheared
environment remains in place ahead of these storms. This should
support a risk for all hazards, include strong tornadoes, very large
hail, and significant damaging winds. Current expectations are for
the individual supercells to grow upscale into one or more clusters
as they interact with a modifying outflow boundary across northeast
KS and northwestern MO. While the environment becomes gradually less
unstable farther north and east, very strong shear will likely
support a continued risk for all hazards this evening. The western
portions of the risk area has been trimmed in parts of central KS
where the cold front has sagged southward.
...Southwest TX..
Strong diurnal heating along southern portions of the dryline has
resulted in isolated storm development this afternoon. Very large
buoyancy (MLCAPE 3000-4000 J/kg) and steep lapse rates will likely
continue to support high-based isolated storms. Vertical shear is
marginal, but sufficient for supercells with hail and damaging wind
potential. Have extended severe probabilities southward along the
dryline.
..Lyons.. 05/18/2026
.PREV DISCUSSION... /ISSUED 1125 AM CDT Mon May 18 2026/
...Central Plains...
Morning water vapor loop shows a potent shortwave trough rotating
across the central Rockies into western KS. The primary surface
boundary extends from western IA into central KS, with a pronounced
outflow boundary associated with overnight convection extending from
southeast KS into southern MO. The outflow boundary will lift
northward today, allowing a very moist and extremely unstable air
mass to spread into eastern KS/northwest MO/extreme southeast
NE/southwest IA. This is the area most concerning for intense
supercells later today.
Initial storms are expected to develop by early afternoon near the
triple point of the retreating outflow boundary and cold front.
These storms will track northeastward through the afternoon and
early evening in a strongly sheared environment favorable for
tornadoes, very large hail, and damaging winds. It remains unclear
how stormscale interactions will impact discrete supercell mode, but
strong tornadoes are a concern in this region.
Farther southwest, thunderstorms will develop in vicinity of the
cold front across south-central KS by late afternoon. Recent CAM
solutions suggest these storms may be affected by the linear frontal
forcing, and may be slightly anafrontal. This would lessen the
tornado risk, but very large hail and damaging winds would remain a
concern. No changes have been made to the Moderate Risk area due to
conflicting model signals.
...Western OK/Northwest TX...
Full sunshine will lead to hot temperatures along the dryline over
western OK into northwest TX. At least isolated thunderstorms are
expected to form in this area, with a risk of large hail and
damaging winds. Weak large scale forcing may limit storm duration
and intensity.
...OH Valley/Great Lakes...
A line of thunderstorms along the IL/IN border is tracking
northeastward into a warm/moist air mass. Relatively strong
low-level wind fields and steep low-level lapse rates suggest a
continued risk of scattered wind damage with the strongest storms as
they track across parts of IN/Lower MI/Northwest OH.
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