Severe Thunderstorm Warning 365, NWS Lincoln, IL

Area Forecast Discussion
National Weather Service Lincoln IL
1223 AM CDT Sat Aug 15 2026

.KEY MESSAGES...

- There is a significant threat of flash flooding across
  portions of central Illinois overnight into early Saturday
  morning, where thunderstorms track over areas that have
  already seen 4-6 inches of rain since Thursday. Areas north of
  a Havana to Bloomington line are most at risk.

- Some of these storms also have the potential to produce
  damaging winds, mainly after midnight.

- The heat and humidity remain a concern for the weekend, with
  the highest chances of seeing more than a 105 degree heat
  index (40-60%) in areas from Beardstown southeast to Marshall.

&&

.DISCUSSION...
Issued at 231 PM CDT Fri Aug 14 2026

The busy weather trend continues, and focus efforts has
primarily been with the first 24-36 hours of the forecast.

Flooding Concerns:

The earlier rainfall has finally moved out, and the Flood Watch
for east central Illinois was cancelled.

Rainfall amounts of 4 to 6 inches were fairly widespread from
the I-74 corridor and then southward in east central Illinois to
I-70. While the earlier watch from Havana-Bloomington northward
was allowed to expire at 10 am, a new watch has been issued for
this area beginning at 10 pm tonight. The next MCS is expected
to develop across Iowa this evening, as an upper wave moves
across that area, and then move into Illinois shortly after
midnight. HREF precipitable water values over 2.2 inches remain
in place overnight across the northern third of Illinois, and
probabilities of over 2 inches of rain tonight are highest from
Galesburg to Lacon (40-60%). However, its LPMM guidance suggests
3-5 inches are a valid concern, depending on where exactly the
MCS tracks. While the flooding is the main focus with this MCS,
there remains a level 2 severe weather threat with it, primarily
for scattered damaging winds.

Heat Concerns:

Extensive rain today has significantly kept temperatures lower
than earlier projections. While skies are now becoming partly
sunny south of I-72, it is unclear whether enough sunshine will
get heat index readings up to 100 degrees in any of the advisory
area today. The current advisory area is expected to have less
impact from the overnight MCS, and guidance continues to point
toward heat index values 105-110 degrees on Saturday and Sunday.
No changes in the Heat Advisory were made in that area for this
reason. Further north, NBM guidance is also showing similar
heat index for Saturday for all of central Illinois. However,
the lingering effects of the next MCS suggest the guidance is
overdoing projections. HREF probabilities of greater than 105
degree heat index on Saturday are highest from Beardstown
southeast through Taylorville to Marshall (40-60%), and tail off
pretty quickly north of there. Will leave any headline changes
for the overnight forecast cycle, once the MCS shows its hand.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1223 AM CDT Sat Aug 15 2026

Thunderstorms are moving across portions of central Illinois during
the early overnight hours and expected to continue into Saturday
morning before exiting east of the area. MVFR/IFR ceilings currently
in place north of the terminals will sink south to along the I-74
corridor overnight, but confidence is currently low that it will
reach as far south as SPI/DEC. Areas that do drop are expected to
improve back to VFR early to mid Saturday afternoon as winds veer to
SWerly.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 10 AM CDT this morning for ILZ027>031-
036>038-040-041-043>046-055-057.
Heat Advisory until 8 PM CDT Sunday for ILZ049>052-061>063-
066>068-071>073.

&&

KEY MESSAGES...Geelhart
DISCUSSION...Geelhart
AVIATION...Deubelbeiss

Hazardous Weather Outlook
National Weather Service Lincoln IL
300 PM CDT Fri Aug 14 2026

ILZ027>031-036>038-040>057-061>063-066>068-071>073-151100-
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-
300 PM CDT Fri Aug 14 2026

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

.DAY ONE...Tonight.

Widespread thunderstorm activity is likely tonight, mainly north of
I-72. Locally strong to severe storms and flash flooding are
possible.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Hot and humid conditions will peak over the area this weekend. Peak
afternoon heat indices will range from 103 to 112 Saturday, and 100
to 105 Sunday.

Daily chances for thunderstorms exist through the weekend, mainly
north of I-70 for Saturday. Some of these storms could be severe and
produce heavy rain.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed after midnight.

37

Preliminary Local Storm Report
National Weather Service Lincoln IL
138 AM CDT Sat Aug 15 2026

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

0135 AM     Flash Flood      Bloomington             40.48N 88.99W
08/15/2026                   McLean             IL   Public

            Several flooded roads reported on Douglas
            Street and viaducts underwater, relayed by
            broadcast media from viewer.

0135 AM     Flash Flood      1 W Normal              40.51N 89.00W
08/15/2026                   McLean             IL   Public

            Adelaide and Bryan streets in Bloomington
            are impassible and underwater, relayed by
            broadcast media from viewer.

&&

Preliminary Local Storm Report
National Weather Service Lincoln IL
146 AM CDT Sat Aug 15 2026

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

0144 AM     Flash Flood      Tremont                 40.53N 89.49W
08/15/2026                   Tazewell           IL   Public

            6 inches of water flowing over E Pearl
            Street.

&&

RAC