Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0744 AM CDT Mon May 18 2026

Valid 181300Z - 191200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL/NORTHEAST KANSAS...SOUTHEAST NEBRASKA...AND FAR NORTHWEST
MISSOURI...

...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 are most likely from central
Kansas and southeast Nebraska into Iowa and northwest Missouri.

...Central Plains into the Midwest/Great Lakes...
Extensive convection continues this morning from western IL into MO
and far eastern KS, aided by warm/moist advection associated with a
40-50 kt southwesterly low-level jet. Gradual destabilization of the
airmass downstream of this ongoing activity is expected today across
the mid MS Valley and Midwest/OH Valley/Great Lakes. Some potential
exists for re-intensification of one or more bowing clusters, with
scattered damaging winds the main concern as low-level lapse rates
gradually steepen. Somewhat less instability and more modest
mid-level flow and related deep-layer shear with eastward extent
into the OH Valley should induce gradual weakening with these
clusters this evening.

The outflow boundary from the morning convection across KS will
likely play a key role in determining the northern extent of
appreciable severe risk later today across the central Plains into
the mid MO Valley. There is concern that this boundary's continued
southward movement this morning and ongoing convection to its north
may hinder/delay destabilization this afternoon ahead of the surface
cold front/dryline. Still, strengthening mid-level flow and
large-scale ascent associated with an ejecting shortwave trough is
expected to overspread the developing warm sector across central KS
into southeast NE by mid to late afternoon.

Even with potential limiting factors such as outflow boundary
placement and residual cloud cover, the presence of very steep lapse
rates aloft (reference 12Z DDC observed sounding) and daytime
heating of a rather moist low-level airmass will likely support
strong to possibly extreme instability south of the cold front and
east of the dryline by early afternoon. Most guidance continues to
suggest that robust thunderstorm initiation will occur by 18-22Z
across central/northeast KS into far southeast NE. These initial
supercells should pose a threat for very large to potentially giant
hail (2-4+ inches in diameter). As low-level shear gradually
increases through late afternoon/early evening in tandem with a
strengthening southerly low-level jet, a focused spatial/temporal
corridor for strong to intense tornadoes should exist across parts
of central/northeast KS into far southeast NE and northwest MO.

Fairly quick upscale growth appears likely by mid to late evening as
thunderstorm mergers/interactions occur, and as the cold front
advances east-southeastward. Even so, a continued threat for QLCS
and embedded supercell tornadoes should continue, as low-level shear
will remain enhanced by a 50+ kt low-level jet. Severe/damaging
winds will also become an increasing concern as convection spreads
eastward in tandem with the cold front. Some severe wind threat may
persist through much of the night since ample instability is
forecast to exist ahead of convection, especially across KS/MO/OK.

...Southern Plains...
Thunderstorm initiation along the dryline this afternoon/early
evening across western OK into western north TX is more uncertain
than locations farther north given expectations for more limited
forcing for ascent. If/where convection does form, there is the
potential for very large hail and a conditional risk for tornadoes
with any persistent supercells, given the presence of steep
mid-level lapse rates, strong instability, moderate deep-layer
shear, and gradually increasing low-level shear this evening. But,
weaker winds above 400 mb by late afternoon/evening may not be
overly favorable for long-lived convection, even if it does form.

...Mid-Atlantic/Northeast...
Influenced by terrain and a surface trough, isolated strong to
severe thunderstorms capable of producing occasional wind damage may
occur this afternoon within a moderately unstable environment.

..Gleason/Marsh.. 05/18/2026