584
FXUS63 KLOT 151936
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
236 PM CDT Sat Aug 15 2026

.KEY MESSAGES...

- Another round of heavy rain producing showers and
  thunderstorms late this evening into Sunday morning.

- A brief break in the stormy pattern is expected Monday into
  early Tuesday before storm chances return ahead of the next
  cold front late Tuesday into Tuesday night.

&&

.DISCUSSION...
Issued at 236 PM CDT Sat Aug 15 2026

The remnant MCV responsible for this morning`s heavy rain
across central Illinois is shifting into northern Indiana this
afternoon. In its wake, widely scattered showers and drizzle
persist within a broad warm air advection pattern. While locally
heavy downpours remain possible, limited coverage should
mitigate renewed flooding concerns through late afternoon.
Expect muggy conditions with temperatures near 80 degrees under
mostly cloudy skies.

Another round of showers and thunderstorms is likely (60%+)
tonight ahead of an approaching cold front and mid-level
impulse. Timing favors an arrival into western Illinois around
and after 10 pm, reaching eastern Illinois and northwest Indiana
after midnight. Poor lapse rates and marginal deep-layer shear
should limit the severe threat, but very heavy rainfall and
localized flash flooding remain concerns given precipitable
water values exceeding 2 inches. While most activity appears
progressive, we are monitoring the potential for backbuilding or
training storms, particularly along the southern periphery of
the MCS as the low-level jet veers overnight. Central Illinois
and Indiana are most at risk, encompassing areas saturated by
this morning`s rainfall. A Flash Flood Watch was considered, but
we opted to hold off due to low confidence in the exact
placement of training cells. The evening shift will continue to
monitor trends to identify high-risk areas.

A cold front will move southeast across the region Sunday,
maintaining a 20-30% chance for scattered showers and
thunderstorms, primarily southeast of I-55. Humidity will be
slow to recover following the frontal passage; expect warm,
humid conditions with highs in the low to mid-80s.

Mainly dry weather is expected Monday and Tuesday as surface
high pressure settles over the Mid-Mississippi Valley. Lower
humidity and slightly cooler temperatures will provide a brief
reprieve before another round of convection arrives late
Tuesday. This next system, driven by a cold front and shortwave
digging into the Great Lakes, brings a renewed threat of strong
storms and heavy rain Tuesday night. Quieter, cooler weather
returns Wednesday and Thursday.

KJB

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1237 PM CDT Sat Aug 15 2026

Key Aviation Messages for the current TAF period:

- Spotty showers are expected to fester through the afternoon
  that may produce localized reduced vis. Best chances for
  scattered showers around 00Z.

- South-southeast winds turn to the southwest this afternoon.
  Low confidence on the exact timing.

- Chance for showers and storms overnight

- MVFR cigs and breezy northwest winds expected tomorrow

Winds are less than 10 knots, and while closer to Lake Michigan
they remain out of the southeast, they are slowly turning to
the southwest and will remain out of the southwest through
tonight.

Widespread showers have diminished across the area, but
weak instability is allowing for isolated showers to persist.
Localized IFR cigs/vis are possible under any downpour,
otherwise light rain is expected. There is about a 30 percent
chance for shower coverage to increase to more widely scattered
around 00Z, but no thunder is expected.

Better chances for showers and thunderstorms arrive tonight as
the next wave (currently entering western Iowa) moves through.
There is still some uncertainty with timing, but narrowed the
window in the TEMPO for arrival just after midnight.

Showers may linger through daybreak behind the wave, but drier
conditions are expected. Unfortunately, MVFR cigs will most
likely remain through much of the day tomorrow. Winds will
slowly turn from the southwest to northwest tomorrow morning
with gusts to 20 knots by late morning/early afternoon.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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