RSS Mesoscale Discussions from Storm Prediction Center
WW 220 SEVERE TSTM IL IN MI OH LM 181505Z - 182200Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 220
NWS Storm Prediction Center Norman OK
1105 AM EDT Mon May 18 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Eastern Illinois
Northern and Central Indiana
Southwest Michigan
Northwest Ohio
Lake Michigan
* Effective this Monday morning and evening from 1105 AM until
600 PM EDT.
* Primary threats include...
Scattered damaging wind gusts to 70 mph likely
Isolated large hail events to 1.5 inches in diameter possible
A tornado or two possible
SUMMARY...A line of thunderstorms over central Illinois will track
northeastward through the day across the watch area. Swaths of
damaging winds are expected with the more intense line segments.
The severe thunderstorm watch area is approximately along and 85
statute miles north and south of a line from 30 miles northwest of
Champaign IL to 55 miles east of Fort Wayne IN. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU0).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.
&&
AVIATION...A few severe thunderstorms with hail surface and aloft to
1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
25035.
...Hart
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WW 0220 Status Updates
STATUS REPORT ON WW 220
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 20 N SLO TO
30 NNE SLO TO 25 SE CMI TO 25 NW DNV TO 45 ESE MMO TO 40 W VPZ TO
45 ESE RFD.
..HALBERT..05/18/26
ATTN...WFO...ILX...LOT...IWX...IND...ILN...
STATUS REPORT FOR WS 220
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
ILC023-025-029-031-033-035-043-045-049-075-079-091-101-159-183-
197-181740-
IL
. ILLINOIS COUNTIES INCLUDED ARE
CLARK CLAY COLES
COOK CRAWFORD CUMBERLAND
DUPAGE EDGAR EFFINGHAM
IROQUOIS JASPER KANKAKEE
LAWRENCE RICHLAND VERMILION
WILL
INC001-003-007-009-011-015-017-021-023-033-035-039-045-049-053-
057-059-063-065-067-069-073-075-081-085-087-089-091-095-097-099-
103-107-109-111-113-119-121-127-131-133-135-141-145-149-151-153-
157-159-165-167-169-171-179-181-183-181740-
IN
. INDIANA COUNTIES INCLUDED ARE
ADAMS ALLEN BENTON
BLACKFORD BOONE CARROLL
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MD 0770 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR LOWER MICHIGAN
Mesoscale Discussion 0770
NWS Storm Prediction Center Norman OK
1138 AM CDT Mon May 18 2026
Areas affected...Lower Michigan
Concerning...Severe potential...Watch likely
Valid 181638Z - 181745Z
Probability of Watch Issuance...95 percent
SUMMARY...A new severe thunderstorm watch will be needed as the
northern edge of a QLCS/Bow Echo moves across Lake Michigan and into
lower Michigan.
DISCUSSION...The northern portion of a bow-echo currently moving
across Lake Michigan will pose a threat for damaging winds gusts
across lower and central Michigan this afternoon. Low-level lapse
rates and strong buoyancy will support continued convective
development along the leading edge of the bow echo, and large DCAPE
will support strong downdrafts capable of 65-80 MPH gusts.
..Halbert/Hart.. 05/18/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CLE...DTX...IWX...GRR...LOT...
LAT...LON 41498662 41608738 41868756 42078775 42168788 42268769
43008587 43398434 43718346 43788295 43668267 43468248
42998230 42468257 42378285 41978316 41688366 41568476
41498662
MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
Read more
Public Severe Weather Outlook
PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0750 AM CDT MON MAY 18 2026
...Severe thunderstorms expected over parts of the south-central
Plains and mid Missouri Valley this afternoon and evening...
* LOCATIONS...
Iowa
Central and Eastern Kansas
Northwest Missouri
Southeast Nebraska
Northern Oklahoma
* HAZARDS...
Several tornadoes, a couple intense
Scattered damaging winds, some hurricane force
Widespread baseball-size hail
* 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.
Preparedness actions...
Review your severe weather safety procedures for the possibility
of dangerous weather today. Stay tuned to NOAA Weather Radio,
weather.gov, or other media for watches and warnings. A tornado
watch means that conditions are favorable for tornadoes to form
during the next several hours. If a tornado warning is issued for
your area, move to a place of safety, ideally in a basement or
interior room on the lowest floor of a sturdy building.
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SPC 1300Z Day 1 Outlook
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
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SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1125 AM CDT Mon May 18 2026
Valid 181630Z - 191200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
AND EVENING OVER PARTS OF EASTERN KANSAS...SOUTHEAST
NEBRASKA...NORTHWEST MISSOURI...AND SOUTHWEST 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 are most likely from central
Kansas and southeast Nebraska into Iowa and northwest Missouri.
...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.
..Hart/Halbert.. 05/18/2026
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Day 4-8 Outlook
Day 4-8 Convective Outlook RESENT 1
NWS Storm Prediction Center Norman OK
0858 AM CDT Mon May 18 2026
Valid 211200Z - 261200Z
...DISCUSSION...
...D4/Thursday - D5/Friday...
On D4/Thursday, a stationary front will extend across the southern
Plains and mid Mississippi Valley and east to the Carolinas.
A few stronger thunderstorms may develop south of this boundary,
however, the strongest upper-level flow will be displaced to the
north, limiting confidence in a more organized severe threat.
Moist southerly return flow will begin across the southern/central
Plains into the weekend. Modest westerly flow across the dryline on
D5/Friday may support some potential for severe storms. Overall,
forcing for ascent will remain limited and there is low confidence
in including a severe risk area at this time.
...D6/Saturday-D8/Monday...
Through the end of the extended period, height rises are expected
across the central US as a high amplitude ridge settles in from the
west. While moisture will continue to move northward into the
central/northern Plains, generally weak flow and subsidence will
keep severe potential low.
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