106
FXUS63 KLOT 010618
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
118 AM CDT Thu Oct 1 2026

.KEY MESSAGES...

- Periods of rain, heavy at times, are expected through early
  Friday morning.

- A large footprint of 1" to 3" rainfall amounts across the
  region may lead to significant rises on area rivers and
  streams.

- The potential exists for localized corridors of rainfall
  amounts in excess of 3" this afternoon and evening.

- Dry and seasonably cool conditions will arrive this weekend
  and continue into early next week.

&&

.DISCUSSION...
Issued at 306 PM CDT Wed Sep 30 2026

Several small-scale mid-level impulses, emanating from a
broader trough shifting across the southern Rockies, continue
to eject east-northeast from the Great Plains into the lower
Great Lakes this afternoon. The initial impulses have supported
a persistent, steady soaking rainfall across much of the area,
particularly along and south of the I-88 corridor. The airmass
remains unseasonably moist due to a continuous deep northward
feed of Gulf moisture. This was confirmed by a derived
precipitable water value near 1.7 inchesa near-record high for
late Septemberfrom a recent Valparaiso University sounding in
northwestern Indiana. Fortunately, a lack of appreciable
instability has kept rain rates manageable, generally below
0.25 inches per hour with only localized corridors reaching 0.5
inches per hour. Consequently, no significant hydrological
concerns are anticipated for the remainder of the day.

The focus for this persistent rain is expected to shift
gradually northward into southern Wisconsin and far northern
Illinois this evening. Shower coverage should temporarily ease
overnight before the next wave arrives with a cold front on
Thursday. A higher concern for torrential rainfall and
associated hydrological impacts exists Thursday afternoon and
evening as low-level lapse rates steepen ahead of the front.
Prefrontal instability will remain focused primarily below the
-10C level, which is unfavorable for lightning production but
highly conducive to efficient warm-rain processes and low
centroid cells given warm-cloud depths reaching 12,000 feet.

We will have to closely monitor the potential for
northeastward- training showers near the frontal boundary
capable of rain rates exceeding 1 inch per hour. Where repeated
heavy rain occurs, localized flash flooding could develop with
totals possibly exceeding 3 inches. While footprint amounts over
3 inches will be localized, broader rainfall totals of 1 to 3
inches are expected across the area through Thursday night,
likely causing aerial flooding and significant river rises
through the end of the week. These threats remain highlighted in
our Hydrologic Outlook.

The surface cold front will push south of the area on Friday,
bringing an end to the wet pattern as high pressure builds in
for the weekend. Dry and cooler conditionstypical for early
Octoberwill prevail for the weekend and early next week, with
high temperatures in the 60s.

KJB

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 118 AM CDT Thu Oct 1 2026

Key Messages:

- Periods of rain will continue through this evening before
  rain tapers off.

- MVFR and IFR ceilings and visibilities are expected at times
  through this evening.

- A northerly wind shift will occur behind a cold front this
  afternoon.


Waves of showers will continue to pass through the C90 airspace
through the remainder of this morning. Primarily VFR conditions
will be favored at the Chicago metro terminals during this
time, though brief MVFR visibility reductions may occur at times
beneath the steadier showers.

A more solid band of rain will set up over the Chicago metro
during the early-mid afternoon, allowing for prevailing MVFR to
IFR conditions to make a return for several hours. This band
will likely set up over RFD earlier, with conditions expected to
deteriorate there by the mid-late morning. There remains only
about a 20% chance that isolated embedded thunderstorms within
this broader rain band may affect the terminals during the
afternoon (mid-late morning at RFD), so have continued to
withhold on any formal TSRA or VCTS mentions in the TAFs. The
rain will then taper off from northwest to southeast during the
evening, with VFR conditions returning at some point thereafter.

Lastly, during today`s rainfall, a cold front will drop across
the area from northwest to southeast. This will result in a wind
shift from southwesterly to northerly winds between midday and
the mid-late afternoon.

Ogorek

&&

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

&&

$$

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