Severe Thunderstorm Warning 359, NWS Lincoln, IL

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

.KEY MESSAGES...

- Flash flooding is a concern along and north of the I-74
  corridor overnight. HREF probabilities of more than 2 inches
  of rain are 30-50% in this area, although some local totals
  over 3 inches are possible.

- Heat index values of 100 to 105 degrees will continue into the
  weekend each afternoon, in areas near and south of I-70. The
  heat is expected to spread northward across the forecast area
  by Saturday.

&&

.DISCUSSION...
Issued at 235 PM CDT Thu Aug 13 2026

MCS that tracked out of Iowa earlier today intensified again as
it crossed the Peoria metro, producing winds around 70 mph and
extensive damage in Bloomington. Cluster of storms has reached
the Champaign area this hour, with the trailing outflow
extending west through Springfield. Storms are riding along a
tight gradient of CAPE and should exit the forecast area in the
next few hours.

Next MCS is expected to begin developing this evening closer to
the warm front from Iowa to northern Indiana, then sink
southward overnight. Precipitable water values over 2 inches
persist through the night, and some of the northern parts of our
forecast area have seen a few inches of rain since yesterday.
HREF PMM precip estimates suggest 1.5-2 inches of rain in 6
hours between midnight and sunrise, and no changes are being
made to the Flood Watch at this time. South half of the forecast
area has a good chance of remaining dry until closer to
daybreak.

Heat forecasts remain a concern as well. Latest guidance
suggests 100-105 heat index could reach as far north as a
Rushville-Paris line tomorrow, but the extent of the lingering
rain/cloud shield introduces some uncertainty as to whether or
not to expand the Heat Advisory. Current inclination is to leave
it in place and allow the next shift to expand it, once the
timing and track of the MCS becomes more certain. An expansion
for the entire forecast area appears more likely for Saturday.

A quick look at the extended forecast -- upper pattern becomes
more zonal for a time as high pressure sprawls more west-east
across the southern U.S. Getting into early next week, riding
amplifies west of the Rockies as a strong upper trough swings
across the Canadian Prairies and the north central U.S. Impacts
from that in our area would be more likely toward the middle of
next week. A couple days of cooler temperatures are likely
early next week, before warming begins again.

&&

.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
DISCUSSION...Geelhart
AVIATION...

Hazardous Weather Outlook
National Weather Service Lincoln IL
304 PM CDT Thu Aug 13 2026

ILZ027>031-036>038-040>057-061>063-066>068-071>073-142015-
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-
304 PM CDT Thu Aug 13 2026

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

.DAY ONE...Tonight.

Heat indices of 95 to 110 are expected this afternoon south of I-72.

Additional thunderstorms are expected late tonight into Friday
morning with damaging winds and large hail possible with any
stronger storms. Heavy rain could locally exceed 3 inches and produce
localized flooding. Areas for strong to severe storms and flooding
will be most likely near and north of I-74

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

Hot and humid conditions will expand northward through late week.
Peak afternoon heat indices will range from 100 to 110 Friday and
Saturday, and Sunday from I-72 southward.

Daily chances for thunderstorms exist through the weekend, although
these will be mainly north of I-72 Friday afternoon through Sunday
morning. Some of these storms could be severe and produce heavy rain
through at least Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed late tonight.

Expected storm motion is toward the east around 30 mph.

37

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