605
FXUS63 KLOT 311144
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
644 AM 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 /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 644 AM CDT Fri Jul 31 2026

Key Messages:

- SHRA develop west-to-east this afternoon.

- Increasing threat for embedded thunderstorms with periods of
  heavy rain and MVFR to IFR conditions late this evening into
  Saturday.

- SSE winds shift easterly and increase later into tonight.

A weather disturbance will gradually shift east-southeastward
across the Midwest into the lower Great Lakes regions today
into Saturday. As it does, rain will develop eastward across
the northern IL terminals into this afternoon (potentially as
early as 15-16Z at RFD and 17-18Z around the Chicago
terminals). Rain showers will then become more pronounced
across the area into tonight as the center of the system begins
to shift into northwestern IL. Steepening mid-level lapse rates
will also support increasing chances for embedded non-severe
storms with heavy downpours, particularly during the late
evening and overnight hours.

At this time, we made no major changes to the going PROB30
mention for TS and lower flight categories tonight. However, if
confidence continues to increase, I could foresee the need to
convert the PROB30 to a prevailing mention of VCTS (or TS) with
+SHRA for at least a few hours after 04Z. Otherwise, expect the
threat for showers (and possibly a few lingering storms) to
linger on Saturday as the parent storm system slowly moves
across the area. MVFR to IFR conditions will also persist as a
result.

Otherwise, south-southeasterly winds today will shift easterly
and increase tonight as surface low pressure begins to shift
into western IL.

KJB

&&

.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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