Severe Thunderstorm Warning 373, NWS Lincoln, IL

Area Forecast Discussion
National Weather Service Lincoln IL
631 PM CDT Fri Aug 21 2026

.KEY MESSAGES...

- A Slight Risk of severe thunderstorms exists this evening
  along and north of a line from Beardstown to Lincoln to Gibson
  City. Hail (15%), wind (15%), and tornado (2%) threats will
  exist in this area, with lower probabilities further south to
  near I-70.

&&

.DISCUSSION...
Issued at 215 AM CDT Fri Aug 21 2026

Weak high pressure ridge ~1018 mb was over near central IL early
this afternoon and providing a delightful late summer day with
mostly sunny skies. Temperatures were in the lower 80s at 2 pm
while dewpoints were in the mid to upper 60s except lower 70s
from Galesburg and Macomb west/nw. A weak cold front was over
central WI into southeast Iowa. Radar mosaic shows scattered
convection over northern IL from I-88 north into southern WI and
tracking ESE. Moderately unstable airmass in place over the IL
river valley where MLCAPES 1500-2500 j/kg nw of I-55 while bulk
shear values of 30-35 kts over IL river valley and over 40 kts
west of IL over central and northern MO. SPC just issued a
mesoscale discussion over northern half of IL north of Lincoln
where severe storm threat is increasing and monitoring a possible
watch box. HRRR and RRFS models show broken band of convection
moving into far northern CWA just after sunset and toward I-55
by late evening, and weakening as it moves toward I-70 around 3
am. SPC continues slight risk of severe storms this evening
along and north of a line from Beardstown to Lincoln to Gibson
City. Hail (15%), wind (15%), and tornado (2%) threats will
exist in the Slight Risk area. CAPES reach 2000-3000 j/kg over
the IL river valley nw of I-55 while wind shear values 30-40 kts
and also in favorable region of se moving upper level jet for
enhanced lift. Further south a Marginal Risk exists as far
southeast as near I-70, with mainly low end hail/wind (5%)
threats for this evening in this area. WPC Day1 outlook has
marginal risk of excessive rainfall over northern CWA this
evening where pockets of 1 inch or more of rain possible on a
saturated ground. But convection bands will be more progressive
than Wed night system so rainfall amounts should be much lower.

Quieter weather is generally expected this weekend into early
next week over central/se IL, though a few model members show
isolated convection (20% or less) over ne CWA Sat afternoon
where MUCAPES get to 1000-1500 j/kg. The stronger short wave
forcing is ne of CWA Sat afternoon over ne IL into northern IN
where better chance of convection will be. A Northwest upper
level flow to prevail over IL through middle of next week with
strong mid/upper level ridge over Southwest States and upper
level low/trof in eastern Canada and northeast US. Another
northern stream short wave disturbance to move se into the
Midwest for middle of next week and bring next chance of
convection around Wednesday though current NBM just has slight
pops over area. Temps to be near a bit below normal early next
week with highs in the upper 70s to lower 80s Sun/Monday and
coolest night Sunday night with lows in mid to upper 50s. Temps
moderate a bit for middle of next week along with increasing
humidity levels/dewpoints with highs back in the low to mid 80s
Tue-Fri (mid to upper 80s southern CWA Wed-Fri).

The Climate Prediction Center (CPC) 8-14 Day Outlook for Aug
29-Sep 4 has 40-50% chance of above normal temperatures over
central/se IL and precipitation trending near normal except
slight above normal near the Indiana border.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 630 PM CDT Fri Aug 21 2026

Primarily VFR conditions at all sites outside of thunderstorms,
but do have MVFR vis when the line of storms does move through
each site this evening. There could be a brief period of cigs
dropping below 3kft but believe it will be when heaviest rain
occurs only. Except for PIA, have started all sites with VCTS
and then a one hr tempo group for when storms will be on site.
Conditions should improve quickly behind the line of storms
after they pass. Expecting scattered clouds tomorrow with
clearing in the afternoon. Winds will be southwest ahead of the
line of storms and then become west to northwest behind them.
Speeds of 10kts of less ahead and behind, but expecting winds
10-15kts tomorrow.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.

&&

KEY MESSAGES...07
DISCUSSION...07
AVIATION...Auten

Hazardous Weather Outlook
National Weather Service Lincoln IL
138 PM CDT Fri Aug 21 2026

ILZ027>031-036>038-040>057-061>063-066>068-071>073-221845-
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-
138 PM CDT Fri Aug 21 2026

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

.DAY ONE...Tonight.

Scattered thunderstorms are possible (30-50% chance) this evening
into tonight. Damaging wind gusts and heavy rain are the main
hazards, however isolated large hail and a brief tornado cannot be
ruled out.

Due to recent heavy rainfall, river flooding is occurring on
portions of the Illinois, Sangamon, and Wabash rivers.

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

Flooding will continue for several days along portions of the
Illinois, Sangamon, and Wabash Rivers.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed later tonight.

NMA

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