118
FXUS63 KILX 122337
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
637 PM CDT Wed Aug 12 2026

.KEY MESSAGES...

- Occasional thunderstorms are expected the next few days. Some
  of these storms may be severe, with locally damaging winds, a
  few tornadoes possible, and isolated large hail.

- Dangerous heat remains a concern through the weekend,
  especially across southern portions of central IL, as
  afternoon heat index values approach 105 daily unless
  thunderstorm activity disrupts afternoon heating.

- A cold front arriving Sunday looks to bring relief from the
  heat for at least a few days by Monday.

&&

.DISCUSSION...
Issued at 251 PM CDT Wed Aug 12 2026

Showers and a few thunderstorms remain over portions of central and
southeast IL which resides in a relatively stationary frontal zone.
With a complex of strong thunderstorms that pushed eastward along
roughly the I-74 corridor this morning, an outflow pushed southward
across much of the area with cooler air and cloud cover tempering
instability across much of the area. However, SPC mesoanalysis
indicates strong MLCAPE around 4000 J/KG lingering south of I-70.
Another shortwave impulse currently initiating thunderstorms near
western portions of I-72 is showing effective bulk shear of 40-50
kts and could drive another complex of severe storms as moves over
that area this evening. SPC maintains a Slight Risk for severe
storms in east-central and southeast IL, with damaging wind as the
highest probability for severe weather (15% risk), but also a 2%
tornado risk and 5% hail risk.

Tonight, most models have a relative lull in thunderstorm activity
despite a few storms developing over the stalled frontal boundary,
however another nocturnal MCS looks to be moving across IA
overnight, heading toward northern or central IL Thursday morning.
High-res ensembles depict 1000-200 J/kg MUCAPE overlapping 30-40 kt
deep layer bulk shear and 100-200 SRH, and additional severe storms
will be possible, for which SPC depicts a Marginal Risk. The pattern
will continue through Friday if not Saturday as well.

On Sunday, a cold front will traverse the area driven by a more
potent shortwave moving through the northern states. Additional
showers and thunderstorms may accompany this frontal passage, then a
quieter period should ensue for early next week.

Highs will range from 80s to lower 90s, with dewpoints well into the
70s, yielding afternoon heat index values approaching 105 daily for
portions of central and southeast IL, especially southern portions.
However, thunderstorm activity will greatly influence temperatures
and heat index, and predictability of heat index remains low. Highs
look to reach only into the 80s for early next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 627 PM CDT Wed Aug 12 2026

Another tricky forecast is on tap for the central Illinois
terminals. Thunderstorms should be done for the night, and as
skies clear, fog and low stratus is expected to develop over the
region. Coverage will be greatest along the I-74 corridor where
IFR vsby and possibly also IFR cigs is expected with lesser
impacts expected further south. Fog should improve by 13-14Z
Thursday morning while MVFR ceilings linger along the I-74
corridor into the afternoon. Another round of strong to severe
thunderstorms will move across central Illinois. Confidence in
timing and location remains very low, as has been the case for
the past several days. Based prob30 timing on the 18Z HRRR
showing a cluster of storms moving southeast across central IL
and impacting the terminals for a 2-3 hour window each.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for ILZ066>068-
071>073.

&&

$$

KEY MESSAGES...37
DISCUSSION...37
AVIATION...Deubelbeiss