Rockford, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

257
FXUS63 KLOT 260613
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
113 AM CDT Wed Aug 26 2026

.KEY MESSAGES...

- Isolated thunderstorms are possible across northern Illinois
  late tonight through daybreak. The strongest storms closer to
  the Wisconsin state line may contain small hail.

- Potential for strong to severe thunderstorms Wednesday
  afternoon and early evening along a cold front, with greatest
  severe threat (level 2 of 5) around and east of a Valparaiso
  to Paxton line.

&&

.DISCUSSION...
Issued at 206 PM CDT Tue Aug 25 2026

An upper-level low centered over the southern Manitoba and
Ontario border will track to east of Lake Superior by Wednesday
evening. Weak mid-level waves rotating around the upper-level
low will cross Wisconsin and clip northern Illinois and
northwest Indiana overnight through Wednesday evening.
Meanwhile, a cold front will cross the forecast area late
Wednesday morning through the afternoon.

The first mid-level impulse will brush the area to the north
overnight. A reservoir of higher 900 to 750 hPa moisture
advecting in from the Missouri River Valley should arrive in
time to interact with a N/S axis of low-level isentropic ascent
and steeper mid-level lapse rates. Expectations are for a broken
to scattered line of showers with embedded thunderstorms to
cross northern Illinois overnight through daybreak Wednesday.
Elevated effective shear may be marginally sufficient for a
couple stronger storms with small hail.

A lull in precip is expected mid to late morning Wednesday.
Guidance has come into better agreement with an incoming cold
front, with latest trends indicating a much faster frontal
passage than what was noted just 24 hours ago. The cold front
likely will have cleared much of the northwest CWA by late
morning, most of the Chicago metro early in the afternoon, and
northwest Indiana mid-afternoon. With deep convection hinging on
destabilization via both daytime heating and advection of
higher mix-layer dew points ahead of the front, trends suggest
that convective initiation may not occur until near or east of a
Valparaiso to Paxton line mid to late afternoon. Conditional on
these storm developing before the front clears most of the
forecast area, deep-layer shear will be favorable for a mix of
supercells and merging multicell clusters. Large hail will be a
threat with discrete cells while damaging wind is of most
concern with any storm.

With the main mid-level wave trailing the cold front by a few
hours, have maintained low-end chance PoPs (under 30%) over
northeast Illinois mid to late afternoon as the post-frontal
environment may not fully stabilize and/or mix-out. Isolated to
widely scattered showers and perhaps a couple narrow but deeper
cores with lightning are possible during this window.

Mid-level ridging over the Canadian Prairies will deamplify
while shifting eastward late this week into the weekend.
Associated surface high pressure will track east while becoming
elongated across the central Great Lakes Thursday and Friday.
Cannot fully rule out sprinkles or weak showers on the lake
breeze boundary across northeast Illinois late Thursday
afternoon, but the subsidence inversion should be strong enough
to stunt growing diurnal cumulus.

A loosely zonal pattern across North America this weekend into
early next week favors a more active storm track north of the
forecast area, but close enough to warrant periods of low-end
precip chances for showers and some thunderstorms as early as
Saturday night (and especially toward Monday and Tuesday).
Summer warmth will also return Sunday and possibly Monday with
increasing humidity and daytime highs pushing well into the 80s
(assuming active weather remains bottled up to the north).

Kluber

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 113 AM CDT Wed Aug 26 2026

Forecast concerns for the terminals...

- Scattered showers and thunderstorms are possible on Wednesday
  (20-40% chance) ahead of a cold front.

- Breezy westerly winds Wednesday afternoon with gusts around
  20-25 kts.


A shortwave trough is pivoting into the northern Great Lakes
with an associated cold front stretching from northern WI to
eastern MN and northern IA. Ahead of these features a band of
showers and embedded thunderstorms have developed in WI and
southeastern MN and these showers/storms are drifting east-
southeast. The expectation is for these showers and storms to
continue to develop overnight as they progress towards northern
IL, but as they near the IL-WI should begin to weaken as they
start to outrun the better instability and moisture. Therefore,
it seems that a broken (isolated to scattered) line of showers
with perhaps some embedded lightning should drift across
northwest IL after 10z and may fully erode before reaching the
Chicago area terminals. Given this expectation have opted to
maintain PROB30s for SHRA at RFD, ORD, and DPA for a few hours
early Wednesday morning to account for a low end chance of a
passing shower should this line hold together, though the
overall thunder threat at these sites looks low (10-15% chance).

By mid-morning on Wednesday, the cold front and shortwave should
be over northern IL and should lead to the redevelopment of
showers and thunderstorms across portions of northeast IL and
northwest IN towards the morning and early afternoon hours.
Depending on where exactly the front is MDW and GYY could be in
play to see a couple hour period of thunderstorms (20-40%
chance) before the activity shifts south and east into central
IL and north-central IN. Furthermore, MDW and GYY could also see
a period of showers Wednesday morning before the redevelopment
occurs if the aforementioned band of showers holds together.
With the forecast for these sites being a bit more complicated
have opted to adjust the PROB30 timing to try to better capture
thunderstorm window and have removed the PROB30 for the earlier
showers as thinking is these should erode prior to reaching MDW
and GYY. Since this forecast is lower confidence this will
obviously be monitored closely. Lastly, there is also a threat
for strong to severe thunderstorms Wednesday afternoon with
damaging winds and hail the main threats, but this threat looks
to largely be east of the TAF sites in northern IN and southern
MI.

Any showers/storms that develop Wednesday should shift away
from the terminals by mid-afternoon and the rest of our area by
late afternoon/early evening. Therefore, the rest of Wednesday
will feature VFR conditions with breezy westerly winds gusting
around 20-25 kts ahead of the front. Behind the front winds will
turn northwesterly and diminish in speeds (around 5-10 kts) by
Wednesday evening where they are expected to remain for the
rest of the TAF period.

Yack

&&

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

&&

$$

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