654
FXUS63 KLOT 311821
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
121 PM CDT Fri Jul 31 2026

.KEY MESSAGES...

- Periods of rain this afternoon through Saturday evening with
  a chance of thunderstorms.

- The potential exists for locally heavy rainfall with areas of
  2"+ rainfall totals.

- High waves and dangerous swimming conditions at Lake Michigan
  beaches late tonight through Monday morning.

&&

.DISCUSSION...
Issued at 151 AM CDT Fri Jul 31 2026

Low pressure will move southeast across IA today then across
south/central IL tonight and across the Ohio River valley
Saturday as it slows. Showers and at least a chance for
thunderstorms will spread across the area this afternoon. As the
low approaches later today, the southern cwa may remain in the
warm sector allowing for a better chance of thunderstorms, a few
of which may be strong to locally severe. Though it appears the
best chance of any severe thunderstorms will remain southwest
of the local area.

Periods of rain will continue tonight into Saturday morning
along with a continued chance for thunderstorms, which current
timing trends would suggest the best chance in the evening into
the early overnight of Saturday morning. The rain during this
time period will likely be moderate to heavy at times with
precipitable water values in the 2 inch range. With the system
slowing as it moves southeast, at least scattered showers are
expected to continue Saturday and these may continue into
Saturday night, especially across northwest IN. Models differ
quite a bit for storm total rainfall but amounts in the 1 to 3
inch range look reasonable, highest amounts across the northern
cwa. There may be some locally higher amounts as well.

A prolonged period of northeast winds is expected, gusting to
30-35 mph across southern Lake Michigan. This will allow for
high waves and dangerous swimming conditions at Lake Michigan
beaches late tonight through early Monday morning and plan to
issue a beach hazard statement with this morning`s forecast.

High pressure will bring dry weather back to the area early next
week with precip chances possibly returning late next week. cms

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 120 PM CDT Fri Jul 31 2026

A low-pressure system with features more characteristic of fall
will drift over the area throughout the TAF period. Expect
several periods of SHRA mixed with summertime convective
elements.

An initial axis of RA/SHRA has already spread across the
terminals early this afternoon. At the Chicago terminals,
visibility and ceilings are expected to remain VFR. At RFD,
periodic MVFR visibility/ceilings are anticipated, with IFR
conditions also possible over the next several hours.

An arc of convection expected to soon develop from southern IA
to central MO will pivot across northern IL tonight, affecting
RFD through much of the night and the Chicago terminals late
evening and overnight. Periodic SHRA with embedded convection is
possible, with the current PROB30 for TSRA likely requiring one
or two targeted windows with TEMPO TSRA. For ORD/MDW, TSRA is
possible anytime from roughly 04-13Z, but will not occur every
hour during this time.

SHRA coverage and intensity will diminish mid to late morning
Saturday. IFR ceilings expected south and west of the terminals
will expand farther north during the morning, particularly with
added low-level moisture off Lake Michigan. While
climatologically uncommon in early August, prevailing IFR
ceilings may be required in the TAF through the morning hours.
Additionally, BR and spotty SHRA/DZ will lower visibility into
MVFR levels.

Diurnal influences combined with marginal low/mid-level rates
should result in a secondary pivoting arc of low-centoid SHRA
and possible TS over or just south of the Chicago terminals
Saturday afternoon. Have included PROB30 TS as the exact
location of this arc of precip remains unclear. However, any
SHRA/TS will produce torrential rainfall rates with low-end IFR
to LIFR visibility. The main precip arc is expected to begin
shifting south of the terminals very late in the TAF period
(early evening).

S winds 10 to 15 knots at TAF issuance will vary between 150
and 200 degrees throughout the afternoon. Winds will then
gradually back and increase through the rest of the period,
shifting E around 15 knots by midnight, and NE 15 to 20 knots
with gusts to around 25 knots Saturday afternoon.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement from late tonight through Monday
     morning for ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement from Saturday morning through Monday
     morning for INZ001-INZ002.

LM...Small Craft Advisory from 3 AM Saturday to 3 AM CDT Monday for
     the IL nearshore waters.

     Small Craft Advisory from 9 AM Saturday to 3 AM CDT Monday for
     the IN nearshore waters.

&&

$$

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