853
FXUS63 KILX 190706
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
206 AM CDT Thu Jun 19 2025

.KEY MESSAGES...

- Summer heat and humidity builds late this week and will persist
  through early next week. High temperatures in the 90s, low
  temperatures in the mid 70s, and afternoon heat indices in the
  low 100s are possible each day Saturday through Tuesday.

- Below-normal rainfall is favored through the next 7 days.
  Normal rainfall for mid June across central Illinois is about 1
  inch per week.

&&

.DISCUSSION...
Issued at 201 AM CDT Thu Jun 19 2025

Low-level clouds and isolated showers continue to linger this
morning within a broad area of cyclonic, wrap-around moisture.
Short-term model guidance strongly supports the idea that clouds
will lift and scatter later this morning as a subsident airmass
works into our region behind a departing frontal system.
Temperatures are forecast to warm into the low-to-mid 80s this
afternoon beneath a mid-level ridge and scattered diurnal cu.

Some uncertainty has emerged for Friday, specifically with the
evolution of an upstream nocturnal MCS. The latest HREF guidance
has introduced a low (< 25%) chance for rain generally north of a
Macomb-to-Danville line. Very dry low-level air out ahead of the
decaying MCS and its attendant mid-level shortwave trough may
ultimately be enough to thwart rain chances across central
Illinois. It could be a case where we just get the anvil cloud
cover and a few sprinkles, but rain or no rain, this convective
debris could play spoiler to upper 80s highs. We have therefore
hedged a few degrees cooler for afternoon highs on Friday.

The weekend then looks convincingly hot and humid but dry as an
upper-level ridge amplifies over the eastern half of the US.
Ambitious mid-level capping (700mb temps > 12C) and robust dry air
entrainment should preclude even isolated showers from developing.
The more obvious risk will be the extreme heat. With afternoon
temps forecast to reach lower 90s amid dewpoints in the 70s, our
confidence is high that peak afternoon heat index values will
surge into the triple digits both Saturday and Sunday, and
possibly Monday. The need for an Extreme Heat Watch is growing
more appropriate, and we may expand the watch into west-central
Illinois as early as today.

The extreme heat risk becomes much less certain by Tuesday as mid-
range global guidance hints at repeated shortwave impulses lifting
across the Plains, perhaps leading to the collapse of the north
and west peripheries of the ridge. The mechanics of this would
coincide with an injection of low-level moisture, raising the
potential for daily, isolated afternoon thunderstorms to return
from Tuesday onward. Any convective activity has the ability to
bust afternoon temperatures, should it develop. Otherwise, the
stretch of triple-digit heat index values may well extend through
the middle of next week.

MJA

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1236 AM CDT Thu Jun 19 2025

An area of showers and IFR-MVFR cigs will be over the central IL
terminals as of 06Z, shifting eastward through the night, with
western terminals KSPI/KPIA returning to VFR conditions by 07-08Z
and eastern terminals KDEC/KBMI/KCMI lingering IFR-MVFR until
13Z-15Z, followed by SCT diurnal cumulus at 3000-5000 ft AGL until
around 00Z. Winds WNW 5-12 kts until 00Z, becoming light and
variable.

37

&&

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

$$