Hail and Damaging Winds in Illinois, April 13, 2026

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1247 PM CDT Mon Apr 13 2026

.KEY MESSAGES...

- Late spring to summer-like temperatures will continue through
  Friday with highs in the 70s and 80s and lows in the 60s.

- Several additional rounds of showers and thunderstorms,
  including a threat for severe weather and flooding, may occur
  as early as today-tonight, but especially Tuesday and Wednesday.

- A brief break in the pattern is expected late Thursday into or
  through the day on Friday before another storm system arrives
  in the Friday evening to Saturday timeframe.

- In the wake of the Saturday cold front, a brief, potentially
  sharp, shot of much cooler air could bring frost/freeze
  concerns into next Sunday and Monday.

&&

.DISCUSSION...
Issued at 338 AM CDT Mon Apr 13 2026

Synopsis:

The transition season will live up to its billing and then some
over the next week. The advertised late spring to summer-like
stormy pattern (with some breaks) will be us through Saturday,
followed by much cooler to possibly downright chilly conditions
Saturday night through Sunday night. The timeframe of greatest
concern for severe weather this week is Tuesday afternoon into
the evening, for which SPC introduced a threat level of 3/5
(enhanced risk) in the overnight day 2 outlook.

Over the next 48 hours, aggregate troughing will become
established across the southwestern United States and reinforce
longwave ridging from the Mississippi River Valley toward the
East Coast. Northeasterly shortwave shedding will support
corresponding episodic surface cyclone development from the
Plains through the Upper Great Lakes, altogether reinforcing a
broad warm sector with late spring to summer-like temperatures
into the region for much of the workweek.

Through Tonight:

The daytime hours today will start out dry but mostly cloudy,
with low clouds near and north of I-80 initially limiting the
diurnal temperature rise. This afternoon, there will be
competing factors regarding whether any convection (likely
rooted above the boundary layer) can materialize.

As the aforementioned aggregate troughing strengthens across
the southwestern US today, a renewed push of southwesterly mid-
level flow will advect a stout EML plume featuring very steep
mid-level lapse rates (>8 C/km) into the Great Lakes. The strong
capping at the base of the EML plume and expected mid-level
height rises typically conceptually point toward dry conditions.
However, we can't ignore the signal on some of the overnight
CAM guidance for scattered thunderstorms on the nose of the EML
this afternoon. Based on an analysis of RAP model fields (which
initialize the HRRR), a possible subtle 700 mb wave with a
defined wind response and appreciable moisture look to be the
key player. Unfortunately, it's a bit too early to tell how
realistic this depiction is (satellite and observational trends
after sunrise this morning should help).

Should the base of the cap be moistened and cooled enough and
updraft attempts overcome the lack of large scale forcing, the
modeled scenario on some of the high-res guidance may very well
come to fruition. Given the competing factors and inherent
uncertainty, opted to introduce 30-40% PoPs translating eastward
this afternoon. If a few robust thunderstorms are able to
develop, effective shear of 30 to 35kt, weak effective inflow,
and steep mid-level lapse rates would support a threat for
supercells with both damaging winds and hail. The threat level
1/5 of in the initial day 1 SPC outlook appears appropriate for
now in light of the highly conditional nature of this setup.
Outside of the uncertain convective potential, expect highs in
the 70s to around 80F (warmest south of I-80) this afternoon,
with southwest winds gusting up to 25-30 mph.

Tonight, there may be a short window of continued potential for
isolated to widely scattered storms this evening (20-30% PoPs),
possibly related to outflow from previous storms (if any indeed
occur this afternoon). Otherwise, intense thunderstorm
development is favored to occur somewhere from central Minnesota
into central Wisconsin as a subtle upper-level shortwave riding
within broad upper-level southwesterly flow induces a low-level
jet atop the stalled warm frontal zone to our north. In the
absence of any convection this evening, attention will turn to
likely activity to our north.

With the northeasterly terminus of the low-level jet pointing
toward the west-to-east oriented instability axis from Wisconsin
and eventually central Lower Michigan, any upscale growth into
a mesoscale convection system should stay decidedly north of our
area. However, should the warm front end up further south than
currently in our forecast (as hinted by HRDPS/ECMWF output),
part of northern Illinois may get a glancing blow by (likely
weakening) storms. Currently don't see this as a particularly
likely scenario, so will cap PoPs at 30-40% from the pre-dawn
through daybreak hours.

Tuesday and Wednesday:

Toward the middle of the week, aggregate troughing will shift
eastward toward the Four Corners Region leading to a
corresponding "nudge" eastward in broad upper-level
southwesterly flow into the Great Lakes. The overlap of the
plume of steep mid-level lapse rates, stalled frontal zone, a
steady feed of low-level moisture advection, and a parade of
shortwaves and the eventual ejection of the aggregate trough
with associated jet maxima to support deep-layer shear will
support a threat for additional waves of severe thunderstorms in
the general region.

Storm modes ranging from convective clusters to supercells with
a threat for all hazards (including very large hail and
tornadoes) will be fair game, particularly on Tuesday. While
there is low confidence in exactly how Tuesday PM will play out
(and how early storms will initiate), the potential is there
for a very favorable setup for damaging to even destructive
hail, which drove the SPC day 2 outlook upgrade (favoring near
and north of I-80). It remains to be seen if locally backed
winds can materialize, with respect to a tornado threat.

Additional, repeated rounds of storms over the same area may
support a threat for flash flooding (possibly even locally
significant) into Tuesday night. Prior rounds of convection into
Wednesday morning may then muddle the picture convectively
speaking for Wednesday PM. Ultimately, pinpointing favored
locations and time windows will remain challenging until there
is better clarity on exact shortwaves and eventual placements of
boundaries.

Thursday through Sunday:

There's variance regarding the progression of a cold front
across the region, with some of the slower solutions holding
onto some potential for storms into Thursday afternoon.
Thereafter, into Thursday night and at least the start of
Friday, ensemble model guidance advertises a brief break in the
stormy pattern as shortwave ridging moves through the Great
Lakes ahead of a substantial trough digging into the central US.
High temperatures look to rebound into the low to even mid 80s
by Friday accompanied by another threat for strong to severe
thunderstorms Friday night into Saturday. Thereafter, there is a
reasonably strong signal in ensemble guidance for a cooldown to
start next week.

The key aspect for the weekend into early next week cooldown is
a recent trend towards a much cooler air mass due to trough
amplification over the region. If this comes to pass, parts of
the area may flirt with sub-freezing temperatures Saturday night
into early Sunday, and again Sunday night into next Monday
morning. With the summer-like warmth and rain this week
supercharging plant growth and leaf out, the magnitude of the
weekend cold shot will be one to watch for agricultural interests.

Castro/Borchardt

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1247 PM CDT Mon Apr 13 2026

Key Aviation Messages for the current TAF period:

- Multiple waves of showers and storms through the evening. Low
  confidence in coverage.

- Gusty southwest winds are expected through the TAF, with a
  chance of erratic gusty southeast winds for a brief period
  after 00Z

- Low level wind shear expected overnight as a low level jet
  increases

- Another chance for showers and storms closer to day break
  tomorrow.

Low level clouds have lifted to higher-end MVFR cigs for most of
the air space. While Chicago terminals are dry at the moment,
scattered showers with embedded thunder has crossed the
Mississippi River and is quickly moving northeast. Model
guidance has struggled with today's event, but surface and
radar observations helped justify converting PROB30s to TEMPOs
and help give a better estimate for showers and thunder at
terminals this afternoon. Winds will remain out of the southwest
with gusts 20 to 25 knots, though stronger gusts associated with
thunderstorms is possible.

While the current trends may be the main show, models (which
have already been mentioned as not handling the event well, thus
lower confidence in what they are projecting) continue to
highlight a second wave of showers and storms after 00Z. PROB30s
were maintained for northern terminals given the lower
confidence in coverage, but TEMPOs were added for MDW/GYY given
the trend in better coverage to the south. Additionally, there
could be a brief window of gusty southeast winds with this
second round of showers and storms tonight, before returning to
the southwest as the showers pass.

After 03Z, a low level jet is expected to increase with winds
exceeding 50 knots just 2000 ft AGL. The threat for low level
wind shear was maintained in the TAF. Most of the region should
remain dry overnight, however, the showers and thunderstorms
impacting Minnesota and Wisconsin during the day/evening today
is projected to move southeast over the airspace tonight. Many
models are suggesting most of the showers and storms will push
out over Lake Michigan. While there is lower confidence in this
final wave of precipitation, it merited a PROB30 inclusion in
the TAF.

Drier conditions are expected after daybreak tomorrow. MVFR cigs
hang on through the morning before eventually lifting to VFR
levels. Winds will remain out of the southwest with gusts 20 to
25 knots. There could we a weak wave in the afternoon that
provides isolated shower chances, but confidence was too low for
mention in the TAF presently.

DK

&&

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

&&

Visit us at weather.gov/chicago

Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
1211 PM CDT Mon Apr 13 2026

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-141715-
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-
1211 PM CDT Mon Apr 13 2026 /111 PM EDT Mon Apr 13 2026/

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

.DAY ONE...This Afternoon and Tonight.

Weather hazards expected...

  Limited Thunderstorm Risk...with an associated:
     Level 2 of 5 Damaging Wind Risk...up to 60 mph.
     Level 2 of 5 Large Hail Risk...up to half dollar size.
  Limited Flooding Risk.

DISCUSSION...

Scattered thunderstorms are expected this afternoon into this
evening, a few severe of these storm may produce instances of large
hail and damaging winds. Locally heavy rainfall is also likely to
accompany these storms.

Additional weakening gusty thunderstorms may approach from the
northwest overnight tonight.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday and Wednesday...
  Elevated Thunderstorm Risk...with an associated:
     Level 3 of 5 Severe Thunderstorm Risk Tuesday.
     Level 2 of 5 Severe Thunderstorm Risk Wednesday.
     Limited Flooding Risk.

Thursday and Friday Night into Saturday...
 Limited Thunderstorm Risk.

DISCUSSION...

Waves of storms are expected Tuesday PM through Wednesday. Some
may be severe with all hazards including flash flooding.

.SPOTTER INFORMATION STATEMENT...

  Spotter reports may be needed this afternoon and evening.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the the east-northeast at around 45 mph.

LMZ740>745-141715-
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-
1211 PM CDT Mon Apr 13 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...This Afternoon and Tonight.

Weather hazards expected...

  Hazardous conditions for small craft.
  Limited Thunderstorm Risk...with an associated:
     Level 2 of 5 Thunderstorm Wind Gust Risk...up to 50 kt.
     Level 2 of 5 Hail Risk...up to half dollar size.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday and Wednesday...
  Hazardous conditions for small craft are likely at times.
  Elevated Thunderstorm Risk...with an associated:
     Level 2 to 3 of 5 Severe Thunderstorm Risk.
Thursday through Saturday...
  Hazardous conditions for small craft are likely at times.
  Limited Thunderstorm Risk at times.
Sunday...
  Hazardous conditions for small craft are likely.

KJB

Visit us at www.weather.gov/chicago