336
FXUS63 KILX 162311
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
611 PM CDT Thu Jul 16 2026

.KEY MESSAGES...

- Persistent heat and humidity will continue to build through
  Saturday. Heat indices peak around 100F today and tomorrow
  and 100-105F Saturday.

- Isolated to widely scattered thunderstorms (20-40% coverage)
  are possible today and tomorrow, mainly during the afternoon
  and evening hours. Locally heavy rain is the primary concern.

- A cold front brings a potential for strong to severe
  thunderstorms Saturday afternoon and evening.

&&

.DISCUSSION...
Issued at 126 PM CDT Thu Jul 16 2026

Synoptic Overview...
This afternoon, surface analysis reveals a split high-pressure
regime with centers located over the Great Lakes and the lower
Mississippi Valley. A neutral point lies between these two
features across central Illinois. Aloft, a robust 590 dam high
is anchored over the Desert Southwest, establishing a persistent
northwest flow downstream across the Great Lakes region.

Heat and Humidity...
Near-term concerns focus on persistent heat and humidity. An
850mb thermal ridge, currently observed near 25C over the
northern Great Plains, is progged to drift eastward across the
Upper Midwest on Friday before settling over central Illinois on
Saturday, where temperatures aloft will ease slightly to around
20C. Daytime highs will remain near 90F today and tomorrow then
into the low 90s Saturday under the thermal ridge axis. Given
dew points in the lower to mid-70s, heat indices are expected to
peak between 100-105F Saturday afternoon.

Convective Outlook...
For today and Friday, moderate instability with MLCAPE values
around 1500 J/kg will be present. In the absence of large-scale
forcing and with weak deep-layer shear (<15kt), the severe
threat remains low. However, isolated to widely scattered
thunderstorms will be possible during peak heating under weakly
or uncapped conditions. Slow storm motions of less than 15 mph
present a risk for localized heavy rain; HREF LPMM guidance
suggests potential for rainfall totals in excess of 2 inches.
In addition, non-supercell tornado parameter values around 1 are
currently observed within the area of ongoing developing
convection south of I-72 suggesting a few brief funnel clouds
may be possible.

Saturday, a robust shortwave trough is expected to dig across
the Great Lakes, driving an attendant surface cold front south
across central Illinois. This boundary will interact with strong
instability, with MLCAPE progged to exceed 3000 J/kg. While
deep-layer shear remains marginal (20-25kt), the timing of the
front appears favorable for peak diurnal heating, potentially
supporting stronger storm development Saturday afternoon and
evening.

Extended Forecast...
Surface high pressure builds over the Great Lakes on Sunday
behind the departing cold front, providing a brief window of
near-normal conditions with highs in the mid-80s. The frontal
boundary is expected to lift north across the region on Monday.
While placement uncertainty exists at this range, a
strengthening low-level jet could drive a nocturnal MCS along
the boundary Monday evening and overnight. By mid-week, a
stronger Canadian high will build south across the northern
Great Plains and Upper Midwest, ushering in drier, slightly
below-normal conditions for the latter half of the week.

Wildfire Smoke...
Canadian and Upper Midwest wildfire activity continues to
produce a considerable smoke plume across the Great Lakes into
New England. Current HRRR near-surface smoke guidance indicates
the southern edge of this plume may graze the I-74 corridor
tonight before shifting north on Friday. While confidence in
significant local impacts remains low, we will monitor trends
closely to determine if current Air Quality Alerts need to be
expanded southward. A secondary, more favorable window for smoke
advection into central Illinois appears possible Saturday
behind the passing cold front, though guidance suggests this may
be in a lower concentration than is currently being observed to
our north today.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 611 PM CDT Thu Jul 16 2026

Scattered showers from KSPI-KCMI southward will fade as sunset
approaches. More numerous showers/storms are expected to develop
beginning early Friday afternoon, and will include a PROB30 at
all terminals for this potential. VFR conditions expected to
prevail, though some brief lower visibilities will accompany the
stronger storms.

&&

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

&&

$$

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