Severe Thunderstorm Warning 354, NWS Lincoln, IL

Area Forecast Discussion
National Weather Service Lincoln IL
1243 PM CDT Thu Aug 13 2026

.KEY MESSAGES...

- Midday Thunderstorm Complex: A cluster of thunderstorms tracks
  across Iowa will likely impact parts of the forecast area,
  with increasing concerns for areas near the Illinois River
  valley. Isolated severe thunderstorms and efficient, heavy
  rainfall are a concern.

- Heat Concerns South: South of the impending thunderstorm
  debris, hot and humid conditions yield heat indices near 105F.
  A Heat Advisory is active through early evening for southeast
  Illinois, and will need to be expanded northward this weekend.

- Overnight Flood Watch: repeated thunderstorms will heighten
  flash flooding risks. A Flood Watch is in effect for counties
  along/north of I-74 through Friday morning.

&&

.UPDATE...
Issued at 935 AM CDT Thu Aug 13 2026

MCS continues to track across southeast Iowa this morning, with
cold cloud tops near -75C. Convective line has maintained itself
and warnings continue to be issued in that area. Ahead of the
system in central Illinois, conditions are fairly stable due to
the extensive low cloudiness and earlier fog across the
northern CWA. However, a NW-SE CAPE gradient may allow for a
path toward the Illinois River Valley in west central Illinois.
None of the reflectivity guidance in the morning CAM's feature
such a scenario at the moment, though various RAP CAPE profiles
do show the gradient aspect. Overall, little change was made for
today's PoP's in that area.

Looking ahead to tonight, the next MCS still appears to set up
near the warm front across northern Illinois this evening,
gradually sinking toward the I-74 corridor toward midnight. Some
minor PoP adjustments were done to increase rain chances near
and north of I-74. No changes were made to the Flood Watch at
this time.

&&

.DISCUSSION...
Issued at 441 AM CDT Thu Aug 13 2026

.Morning Dense Fog...

A strong radiational cooling regime early this morning has
fostered patchy dense fog development across central Illinois.
Despite high-level anvil debris streaming overhead near/north
of the I-74 corridor around midday, bringing a threat for
upstream convection, lingering near-surface moisture and weak
boundary- layer flow (winds < 10 kt through 3 kft) will keep fog
grounded past daybreak. Shallow warm air advection (WAA)
overrunning the effective surface boundary currently draped just
south of the forecast area will also aid in maintaining low
stratus/fog well into the mid-morning hours. A Dense Fog
Advisory is in effect through 9 AM CDT for locations roughly
north of a Quincy to Terre Haute line.

.Midday Convective Complex & Heavy Rain Potential...

Attention then shifts to the afternoon as the first of multiple
convective rounds approaches from the west. Early morning radar
trends reveal a MCC positioned over western IA. Short- term
high- resolution guidance remains in solid consensus that this
complex will track near and north of the I-74 corridor by
midday, riding along the nose of a receding low-level jet (LLJ),
a convectively-augmented shortwave trough, and the northern
edge of the instability gradient.

Severe potential with this initial wave remains conditional.
While cold pool dynamics and potential Rear Inflow Jet (RIJ)
organization bear watching, poor lapse rates, lingering morning
fog/stratus, and a persistent low-level temperature inversion
could keep this incoming activity elevated and predominantly
sub-severe.

Regardless of severe risk, this initial round will be an
efficient heavy rainfall producer. Atmospheric soundings display
classic tropical-like characteristics: (a) anomalous PWAT
values (2-2.2 inches); (b) low- to mid-level RH exceeding 80%;
(c) a deep warm cloud layer (> 4km); and (d) a long, skinny
CAPE profile.

Latest HREF 6-hour Probability-Matched Mean (PMM) QPF targets
0.5 to 1.5 inches across the northern forecast area with this
initial midday push.

.Heat & Humidity Across the South...

South of the convective footprint and the effective surface
boundary (primarily south of a Quincy to Terre Haute line),
strong surface heating and rich moisture will persist. Highs
near 90 paired with dewpoints in the mid 70s will yield heat
index values between 100-105F. A Heat Advisory is in effect
through early evening for portions of southeast Illinois.

.Overnight Flash Flood Threat...

The threat for flash flooding escalates significantly tonight
across central and northern Illinois. The effective surface
boundary will begin to retreat northward as a sharpening warm
front. An intensifying nocturnal LLJ impinging directly onto
this elevated baroclinic zone will fuel repeated convective
initiation and training thunderstorm complexes near and north of
the I-74 corridor.

With antecedent conditions potentially primed by the midday
convective round, susceptibility to rapid runoff could be high.
HREF QPF PMM guidance indicates an additional 1-2 inches
overnight, with mesoscale training corridors capable of
producing localized totals exceeding 4 inches. Given the high-
efficiency airmass and high potential for training, a Flood
Watch has been issued for counties along and north of I-74
through Friday morning.

.This Weekend Through Mid-next Week...

The surface warm front is projected to surge north of the area
Friday night into Saturday, re-introducing triple- digit heat
indices and scattered elevated warm-advection convection to
start the weekend. The Heat Advisory will most likely need to be
expanded northward for Friday and Saturday.

A stronger, more potent shortwave trough is then forecast to
dig out of the Northern Plains Sunday into Monday, driving a
sharper surface cold front through the Mississippi Valley. While
showers and thunderstorms may accompany the frontal passage,
deterministic models and global ensembles show remarkably strong
consensus for a deeper continental polar (cP) airmass to push
into the central U.S. early next week. This will usher in a
period of below-normal temperatures, lower dewpoints, and an
extended break from the active convective pattern by Monday and
Tuesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1243 PM CDT Thu Aug 13 2026

Cluster of severe storms just passed KPIA and will likely make
it to KBMI shortly after 18z if they hold together. Another
round of storms is expected to develop across northern Illinois
this evening and sink southward, though arrival at the northern
terminals (KPIA/KBMI) would probably be closer toward 07-09z or
so. These would be accompanied by deteriorating ceilings from
north to south overnight, with MVFR conditions most likely from
KPIA-KCMI. Southern extent is more questionable, but heavier
showers may result in some brief visibility drops into that
range.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday morning for ILZ027>031-037-038-045-
046.
Heat Advisory until 8 PM CDT Sunday for ILZ066>068-071>073.

&&

KEY MESSAGES...Geelhart
UPDATE...Geelhart
DISCUSSION...MJA
AVIATION...Geelhart

Hazardous Weather Outlook
National Weather Service Lincoln IL
500 AM CDT Thu Aug 13 2026

ILZ027>031-036>038-040>057-061>063-066>068-071>073-141000-
Knox-Stark-Peoria-Marshall-Woodford-Fulton-Tazewell-McLean-Schuyler-
Mason-Logan-De Witt-Piatt-Champaign-Vermilion-Cass-Menard-Scott-
Morgan-Sangamon-Christian-Macon-Moultrie-Douglas-Coles-Edgar-Shelby-
Cumberland-Clark-Effingham-Jasper-Crawford-Clay-Richland-Lawrence-
500 AM CDT Thu Aug 13 2026

This Hazardous Weather Outlook is for central Illinois, east
central Illinois, southeast Illinois and west central Illinois.

.DAY ONE...Today and tonight.

Heat indices of 95 to 105 are expected this afternoon south of I-72.

A thunderstorm complex will move through central Illinois from late
morning through afternoon. Damaging winds gusts are the primary
threat, though a couple tornadoes cannot be ruled out. Additional
storms are expected late tonight into the overnight hours with
damaging winds and large hail possible with any stronger storms.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Hot and humid conditions will expand back northward through late
week. Peak afternoon heat indices will range from 95 to 105 Friday
through Sunday areawide.

Daily chances for thunderstorms exist through the weekend. Some of
these storms could be severe and produce heavy rain through at least
Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed later this morning into afternoon.

Expected storm motion is toward the east at 40-45 mph.

NMA

Preliminary Local Storm Report
National Weather Service Lincoln IL
936 AM CDT Thu Aug 13 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0700 AM     Rain             3 N Galesburg           40.99N 90.38W
08/13/2026  M2.48 Inch       Knox               IL   Cocorahs

            Cocorahs station IL-KX-24 Galesburg 2.5 N.
            The period of the Rain event was 24 hours.

0700 AM     Rain             3 NE East Galesburg     40.97N 90.27W
08/13/2026  M2.25 Inch       Knox               IL   Cocorahs

            Cocorahs station IL-KX-26 Galesburg 5.7 E.
            The period of the Rain event was 24 hours.

0700 AM     Rain             1 W Galesburg           40.95N 90.39W
08/13/2026  M2.20 Inch       Knox               IL   CO-OP Observer

            CO-OP Observer station GBGI2 Galesburg. The
            period of the Rain event was 24 hours.

0700 AM     Rain             1 NW Knoxville          40.91N 90.29W
08/13/2026  M1.95 Inch       Knox               IL   Cocorahs

            Cocorahs station IL-KX-9 Knoxville 0.7 NW.
            The period of the Rain event was 24 hours.

0800 AM     Rain             3 S Dahinda             40.89N 90.10W
08/13/2026  M1.80 Inch       Knox               IL   Cocorahs

            Cocorahs station IL-KX-27 2 SSE Dahinda. The
            period of the Rain event was 24 hours.

0800 AM     Rain             Knoxville               40.90N 90.29W
08/13/2026  M1.40 Inch       Knox               IL   CO-OP Observer

            CO-OP Observer station KNXI2 Knoxville. The
            period of the Rain event was 24 hours.

0630 AM     Rain             2 WSW Elmore            40.95N 90.01W
08/13/2026  M1.35 Inch       Knox               IL   Cocorahs

            Cocorahs station IL-KX-23 Williamsfield 1.7
            NNE. The period of the Rain event was 24
            hours.

0645 AM     Rain             Yates City              40.78N 90.02W
08/13/2026  M1.13 Inch       Knox               IL   CO-OP Observer

            CO-OP Observer station YATI2 Yates City. The
            period of the Rain event was 24 hours.

0700 AM     Rain             3 SE Henderson          40.99N 90.31W
08/13/2026  M1.10 Inch       Knox               IL   Cocorahs

            Cocorahs station IL-KX-29 Wataga 3.0 SW. The
            period of the Rain event was 24 hours.

&&

Special Weather Statement
National Weather Service Lincoln IL
1108 AM CDT Thu Aug 13 2026

ILZ027-036-131700-
Knox-Fulton-
1108 AM CDT Thu Aug 13 2026

...STRONG THUNDERSTORMS WILL IMPACT NORTHERN FULTON...KNOX AND
SOUTHWESTERN PEORIA COUNTIES THROUGH NOON CDT...

At 1107 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near New Windsor to near St. Augustine.
Movement was east at 45 mph.

HAZARD...Wind gusts up to 40 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Galesburg, Canton, Abingdon, Knoxville, Farmington, Wataga, Avon,
Oneida, Yates City, Williamsfield, Altona, Fairview, London Mills,
Victoria, Maquon, Henderson, Rio, St. Augustine, East Galesburg, and
Norris.

This includes Interstate 74 between mile markers 35 and 68.

This also includes Snakeden Hollow State Fish and Wildlife Area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with these storms and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4115 9001 4109 8998 4063 8999 4062 8988
      4061 8988 4047 9045 4115 9044
TIME...MOT...LOC 1607Z 249DEG 37KT 4116 9047 4074 9034

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

AAT

Special Weather Statement
National Weather Service Lincoln IL
1200 PM CDT Thu Aug 13 2026

ILZ027>031-036-037-131745-
Tazewell-Marshall-Peoria-Knox-Woodford-Stark-Fulton-
1200 PM CDT Thu Aug 13 2026

...STRONG THUNDERSTORMS WILL IMPACT MARSHALL...WESTERN WOODFORD...
FULTON...STARK...KNOX...TAZEWELL...AND PEORIA COUNTIES THROUGH 1245
PM CDT...

At 1200 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from Wyoming to Cuba. Movement was east at 45 mph.

HAZARD...Wind gusts up to 50 mph and penny size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Peoria, Pekin, Galesburg, East Peoria, Morton, Canton, Chillicothe,
Eureka, Lacon, Wyoming, Toulon, Washington, Bartonville, Creve Coeur,
West Peoria, Metamora, Germantown Hills, Abingdon, Knoxville, and
Marquette Heights.

This includes the following highways...
 Interstate 155 between mile markers 21 and 31.
 Interstate 474 between mile markers 0 and 14.
 Interstate 74 between mile markers 34 and 115.

This also includes Banner Marsh State Fish and Wildlife Area, Jubilee
College State Park, Marshall State Fish and Wildlife Area, Powerton
Lake State Fish and Wildlife Area, Rice Lake State Fish and Wildlife
Area, Rock Island Trail State Park, Snakeden Hollow State Fish and
Wildlife Area, Spring Lake State Fish and Wildlife Area, Woodford
State Fish and Wildlife Area, and Mackinaw River State Fish and
Wildlife Area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with these storms and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4115 8964 4115 8933 4110 8935 4110 8927
      4060 8922 4059 8927 4047 8926 4041 9045
      4115 9044 4115 8987 4123 8986 4124 8964
TIME...MOT...LOC 1700Z 262DEG 51KT 4106 8975 4049 9022

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

AAT

Preliminary Local Storm Report
National Weather Service Lincoln IL
1240 PM CDT Thu Aug 13 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1218 PM     Tstm Wnd Dmg     1 N Mossville           40.83N 89.57W
08/13/2026                   Peoria             IL   Public

            Tree down at Route 29 and Route 6.

&&

Preliminary Local Storm Report
National Weather Service Lincoln IL
1246 PM CDT Thu Aug 13 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1205 PM     Tstm Wnd Dmg     Canton                  40.56N 90.04W
08/13/2026                   Fulton             IL   Emergency Mngr

            Tree down on W. Myrtle St.

&&