Naperville, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

914
FXUS63 KLOT 200832
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
332 AM CDT Thu Aug 20 2026

.KEY MESSAGES...

- Less humid today with temperatures in the mid 70s to lower
  80s.

- Showers and thunderstorm chances return Friday and Friday
  night with the greatest coverage in the late afternoon and
  evening. Primary hazards include strong winds and hail in
  addition to localized downpours.

&&

.DISCUSSION...
Issued at 332 AM CDT Thu Aug 20 2026

Showers and thunderstorms have pushed southeast of the area
early this morning with surface high pressure beginning to
expand across the region in their wake. Accordingly, expect
decreasing cloud coverage through the morning. Can`t fully rule
out patchy shallow fog development toward daybreak, mainly
across interior northern Illinois. Temperatures are then
forecast to warm into the upper 70s to lower 80s today away from
the cooler lakeshore areas. With dewpoints likely mixing down
into the 50s and lower 60s, heat indices should remain in check,
making for a pleasant weather day and a much needed break in
what has been a relentless and humid weather pattern.

Attention then turns to Friday when a series of waves will move
within the broader west northwest upper level flow across the
region. This will bring the potential for showers and
thunderstorms back to the area Friday morning through Friday
night. The first of which may arrive in the form of a decaying
cluster of showers and thunderstorms in the morning out of
Wisconsin associated with a wave currently over southern
Saskatchewan/Manitoba. Several CAMs suggests the majority of
this activity may erode entirely before it reaches the I-88/80
corridors given the very dry antecedent airmass.

While it may erode with southward extent, this first "round"
may help to locally increase the low to mid level moisture
which could play a role in additional development later into the
afternoon and evening when a trailing wave/vort lobe drifts
across the area. This wave may prove sufficient for initiating a
new round of convection across northwest IL ahead of an
approaching surface cold front in the afternoon that then moves
across the area into the evening. Increasing mid-level flow,
especially across areas southwest of the Chicago metro, suggests
that at least strong to locally severe storms may be able to
form along the front. It is possible that a Level 1 of 5 threat
for severe weather ends up needing to be expanded east to
include portions of northern Illinois with later updates if this
signal persists.

A stronger mid-upper wave is then progged to dive across the
Great Lakes into Saturday. While low-level moisture will be be
decreasing in the wake of Friday`s storms and trailing cold
front, a low-level convergence axis paired with mid-level
forcing with the wave may be sufficient to result in at least
isolated shower and storm development inland of Lake Michigan
and have maintained 15-20% chances with this update to account
for this potential.

Dry conditions are then forecast early next week as upper
ridging builds back into the region. Seasonably cool
temperatures are expected on Sunday with highs in the low to mid
70s due to continued onshore flow. Temperatures then very
gradually increase through midweek back into the lower 80s. A
disturbance moving atop the upper ridge across Ontario may swing
an associated surface cold front across the region in the
Tuesday-Wednesday timeframe bringing our next chance for
showers and thunderstorms to the region.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1236 AM CDT Thu Aug 20 2026

High pressure building over the area will bring VFR conditions
with periods of upper-level cloud cover throughout the forecast
window. Light and sometimes VRB winds (but favoring NNE) are
expected through mid-morning. ORD/MDW may see a brief period
around sunrise when winds are just W of N (e.g. 340-000 degrees)
at around 5 knots, but should return to E of N within an hour
or two after sunrise. A lake breeze will then solidly shift
winds NE around 10 knots late morning through the afternoon.
Light and VRB winds around or less than 5 knots tonight will
favor the SE quadrant in the evening and SW quadrant overnight
into Friday morning.

Kluber

&&

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

&&

$$

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