Flash Flooding and Flood in Illinois, April 3 to 4, 2026

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
909 PM CDT Fri Apr 3 2026

.KEY MESSAGES...

- Scattered thunderstorms tonight with heavy rain/localized
  flooding.

- A transition toward a quieter, but cooler, pattern is on track
  to arrive Sunday through early next week before milder and
  more active weather returns for the second half of the week.

&&

.UPDATE...
Issued at 909 PM CDT Fri Apr 3 2026

This evening, we find a warm front draped across central IL,
just south of our CWA boundary as of 9 PM. A cluster of
thunderstorms is lifting near and north of the front and just
recently have began pushing into the Chicago metro area from the
southwest. The strongest storms thus far this evening have been
those forming along the front over central IL, but they've been
consistently weakening as they lift north of the front and into
our southern CWA. A handful of likely severe storms managed to
scoot across our southern-most counties earlier in the evening.
However, the severe threat now appears to be winding down and
heavy rain and flooding are our primary concerns for the
remainder of the night.

We'll continue to see densely scattered shower and storm
coverage fill in across the area through the remainder of the
evening and into the overnight. Temperatures are down into the
upper 40s across our south, so any additional storms down there
will be safely elevated north of the front and no longer pose a
tornado threat. This prompted us to recently cancel the tornado
watch previously issued across our southern CWA. Some small hail
will remain possible with any deeper cores through this evening
with respectfully steep mid level lapse rates, but anything
severe is beginning to look out of reach.

A line of showers and embedded storms will then progress east
across the area overnight into the early morning hours ahead of
the storm's cold front. The center of the low will track across
the IL/WI state line and the warm front will surge northward
across our area ahead of it which should cause temperatures to
warm a few to several degrees during the night, particularly
near and north of I-80. However, by this time, parameter spacing
does not look very conducive of severe convection. However,
with a building LLJ overhead and LFC dropping closer to the
surface ahead of the front, storms overnight could feature some
locally stronger wind gusts.

The main concern, however, with storms through the remainder of
the night is heavy rain and instances of flash flooding. Recent
rains have much of the area especially susceptible to flash
flooding and a number of gauges on area rivers are already at or
on their way to flood stage. And especially as we move into the
night and precip coverage around the area increases, tall,
skinny CAPE profiles and weak shear amid deep layer forcing and
saturation will continue to promote pockets of soaking
downpours. Guidance and recent trends generally favor areas
near the I-55 corridor to receive the most rain through the
night and this area will be more susceptible to instances of
training convection than areas northwest. However, flash
flooding will be possible anywhere around the area tonight.
We've already gotten a jump on some flood products this evening
having issued a preemptive flash flood watch around the whole
CWA into tomorrow morning. And recent storms had prompted us to
issue a flash flood warning for a large portion of Livingston
County. Will keep a close eye on obs and radar trends as I
imagine we will see the need for additional flood products
before the night's out. Updated forecast products have been
sent.

Doom

&&

.DISCUSSION...
Issued at 225 PM CDT Fri Apr 3 2026

Primary forecast concerns are severe and heavy rain potential
through tonight.

A cold front (lake enhanced) is moving across the area now with
northeast winds currently through the I-80 corridor. this front
will continue moving south into the Illinois and Kankakee River
valleys later this afternoon and possibly into the far southern
cwa by early this evening. This will confine the tornado
potential to the far southwest/southern cwa later this afternoon
and this evening, leaving just mainly a limited hail potential
for the rest of the area. Models have been in fair agreement
with convection developing during the late afternoon across west
central IL and then lifting northeast across the metro area
through the evening. Ahead of this potential, at least isolated
thunderstorms are possible across northwest IL with the
activity currently across northeast IL. There may be a brief
lull in the late evening then another round of showers and
thunderstorms are expected overnight, affecting most of the
area. The main threat during this time period will be heavy
rainfall (which is also possible this evening), which may lead
to localized flooding. Given how much rain has already fallen
over recent days, the saturated soils and elevated rivers/
streams, its possible flooding may develop a bit faster if heavy
rain remains over the same areas. Thus the flooding potential
will need to be monitored closely this evening and overnight.

A cold front will move across the area Saturday with showers
likely during the morning until the front actually moves
through, though there remains uncertainty for how widespread the
showers will become as well as the end time. While the bulk of
the heavier showers and remaining thunderstorms should be
exiting the eastern cwa around/after daybreak, only medium
confidence for precip trends/end times Saturday morning.

Westerly winds will steadily increase Saturday morning and may
gust as high as 35 mph in the afternoon/early evening and then
begin to slowly diminish Saturday evening, though it will still
remain breezy/windy Saturday night into Sunday morning. The
gradient begins to weaken Sunday afternoon, which may allow for
a lake breeze, at least into northwest IN Sunday afternoon.

A stronger cold front is expected to move south across the local
area Sunday night, bringing colder temperatures. Generally dry
weather is expected during this time period though a few
flurries are possible. Depending on how cold the airmass
eventually becomes, there could be some lake effect snow
showers/flurries but the potential looks low at this time.

Southerly flow and warmer temps return midweek ahead of another
cold front that may become stationary across the local area
through the end of next week, making for a possible unsettled
pattern to return to the area. cms

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 633 PM CDT Fri Apr 3 2026

Scattered showers and thunderstorms will expand into northern
IL and northwest IN into the evening with coverage looking to
approach the Chicagoland terminals after 02Z. Precip is already
beginning to move into RFD's vicinity as of 2330Z. Higher
coverage of showers and embedded storms is anticipated during
the earlier half of the overnight as a cold front works across
northern IL. The thunder threat should wrap up by around 09Z
with showers lingering into the early morning. Prevailing MVFR
vsbys appear likely through the night with periods of IFR
possible.

MVFR cigs have settled over the TAF sites early this evening.
MVFR will prevail through the evening with periods of IFR
possible beneath precip. IFR cigs look to take hold for the
overnight with LIFR possible, particularly toward daybreak.
Improvements to MVFR are anticipated after daybreak with a
return to VFR expected in the early afternoon.

ENE winds will gust to between 20 and 25 kt through this
evening, locally higher near storms. They'll generally ease
closer to 10 kt and veer to SE for the overnight, but with the
occasional gust still possible. Looking like a marginal LLWS
setup for late tonight with as many as 40 kt of SSW flow at 2
kft AGL, but did not include a LLWS mention in the TAFs. Expect
SW to W winds tomorrow gusting to 25 occasionally up to 30 kt
for the late morning and afternoon. W winds will remain breezy
through the evening.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch through Saturday morning for ILZ003-ILZ004-ILZ005-
     ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-
     ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-
     ILZ106-ILZ107-ILZ108.

IN...Flood Watch through Saturday morning for INZ001-INZ002-INZ010-
     INZ011-INZ019.

LM...None.

&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
914 PM CDT Fri Apr 3 2026

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-050215-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
914 PM CDT Fri Apr 3 2026 /1014 PM EDT Fri Apr 3 2026/

This Hazardous Weather Outlook is for portions of north central
Illinois...northeast Illinois and northwest Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  Elevated Thunderstorm Risk...with an associated:
     Level 1 of 5 Damaging Wind Risk...up to 60 mph.
     Level 1 of 5 Large Hail Risk...up to one inch in diameter.
  Elevated Flooding Risk.

DISCUSSION...

Scattered thunderstorms will continue through this evening with
small hail and locally gusty winds possible with the strongest
storms, especially those south of US Route 24.

Thunderstorms will become more numerous and spread across the
area overnight. The primary concern overnight will be heavy rain
that may result in flash flooding and river rises.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Saturday Morning...
  Limited Thunderstorm Risk east of I-57.

DISCUSSION...

.SPOTTER INFORMATION STATEMENT...

  Spotters may be needed through this evening south of US Route 24.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the northeast at 25 to 30 mph.

LMZ740>745-050215-
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
914 PM CDT Fri Apr 3 2026

This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.

.DAY ONE...Tonight.

Weather hazards expected...

  Hazardous conditions for small craft.
  Limited Thunderstorm Risk...with an associated:
     Thunderstorm Waterspout Risk
     Level 1 of 5 Thunderstorm Wind Gust Risk...up to 50 knots.
     Level 1 of 5 Hail Risk...up to one inch in diameter.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Saturday through Thursday...
  Hazardous conditions for small craft are likely.

Doom

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