Chicago, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

612
FXUS63 KLOT 051730
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1230 PM CDT Sun Apr 5 2026

.KEY MESSAGES...

- Scattered showers tonight, mainly north of about I-80.

- Brief chance for a light rain/snow mix Tuesday night.

- Sub-freezing temperatures expected Monday night, but warmer
  conditions develop Wednesday through the end of the week.

- Periods of showers and storms are possible late in the week
  into next weekend.

&&

.DISCUSSION...
Issued at 1230 PM CDT Sun Apr 5 2026

Water vapor loops reveal a vigorous shortwave pushing into NW
Minnesota early this afternoon. This wave and an attendant cold
front will sweep into northern Iowa late this afternoon where
recent guidance depicts diurnally-increasing low-level
instability as 700-500 mb temperatures cool. Given the
magnitude of forcing, it seems likely that at least isolated
low-topped/shallow convection will develop into northeast Iowa
towards early this evening within a small corridor of ~200 J/kg
MLCAPE and then track southeastward through late evening.

Preceding this wave, somewhat steep lapse rates are forecast
around 700 mb across our region this evening. Latest RAP
guidance depicts significant lifting and moistening of this
conditionally unstable layer along and immediately ahead of the
main surface trough, and the eventual development of a MAUL
(moist absolutely unstable layer) coincident with the arrival of
strongest forcing after 10 PM (although not through a
particularly deep layer). Thus, while any shallow/low-topped
convection that developed in the afternoon across Iowa should
weaken with the loss of (already meager) surface-based
instability due to boundary layer cooling, scattered showers
and perhaps a rogue lightning strike may continue into northern
Illinois late this evening and overnight along with periodically
gusty winds. Lower precip chances exist generally south of
about I-80, and any lingering activity will diminish and/or push
east of the region by 3- 4 AM.

Modest pressure rises in the wake of the passing cold front will
deliver another period of blustery northwesterly winds to the
region on Monday. Latest guidance suggests a brief period of
gusts up to 35 mph will be possible mid-late morning across
northeast Illinois before gusts generally settle into the 20-30
mph range in the afternoon. High temperatures will likely
struggle to get out of the 40s north of I-80, while low to mid
50 degree readings will be more prevalent to the south. Morning
stratus should eventually give way to some diurnal cumulus
buildups during the afternoon. While a stray sprinkle can`t be
ruled out, limited cloud depths and a lingering warm layer above
800 mb preclude the inclusion of any precip chances at this
time.

Towards early evening, a sharp trough axis and associated
secondary front are forecast to drop down the lake, near the
Wisconsin state line vicinity. Some of the most aggressive
guidance develops some strongly-forced snow showers along the
convergence axis into Monday evening within a lingering axis of
some low-level instability. At this time, not seeing a ton of
support for the farther southwest and more aggressive HRRR/RAP
solutions, but something to keep an eye on as the environment
would support some threat for more robust snow showers into
Monday night.

A mid 1030s mb surface high will nose in from the north through
Tuesday morning. While northeasterly winds will remain a bit
elevated through the night, persistent cold advection will send
temperatures into the 20s across the entire forecast area. Moist
onshore flow will support the development of stratus,
particularly near the lake Tuesday morning, followed by some
increase in mid and high cloud cover through Tuesday afternoon.

Warm advection will then increase Tuesday night as 925-850 mb
flow turns southwesterly in response to cyclogenesis across the
central Great Plains. As winds increase in the vicinity of a
northward-advancing mid-level baroclinic zone, 850-700 mb
frontogenesis will increase across the region Tuesday night
which will force a NW-SE oriented band of light precipitation
across parts of the forecast area. At this time, it remains a
bit unclear just how expansive precip coverage will be with some
lingering dry air near the surface. That said, there is decent
ensemble agreement suggesting that NBM PoPs may be a bit
underdone (somewhat typical in these light QPF regimes). For the
time being, have not made significant alterations given this is
still a few days out, but there will be a potential for some
light snow--at least initially--before the columns steadily
warms through the night. While there may technically be a chance
for a very brief period of freezing rain due to surface
wetbulbs lingering below freezing as 850 mb temps warm, not
concerned about this prospect given the trend for surface
temperatures to warm rapidly with time.

After any lingering precip ends early Wednesday morning, the
rest of Wednesday looks dry with increasingly gusty south-
southwesterly winds through the day. Forecast soundings suggest
the NBM-delivered wind gusts are a bit too low Wednesday
afternoon, with some potential for peak gusts nearing 40 mph if
thicker cloud cover clears out through the morning.

An additional fast-moving wave will bring the next chances for
showers to the region Wednesday night into Thursday morning.
While a few embedded storms can`t be ruled out, instability
currently looks pretty meager. Beyond this period, the forecast
evolution becomes a bit more unclear. A cold front is forecast
to push towards and into parts of the region sometime during the
Thursday-Thursday night timeframe with another round of showers
before potentially stalling either across our far south of very
nearby. Additional waves traversing the region to the north and
west of the frontal zone could support rounds of additional
convection through Friday night, but this evolution is very
uncertain at this range. Thereafter, an active weather pattern
looks like it`ll continue as another synoptic southern stream
wave rolls out of the Great Basin beyond the end of next
weekend.

Carlaw

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1230 PM CDT Sun Apr 5 2026

- Brief period of scattered showers tonight followed by MVFR
  cigs through mid-late morning Monday.

- Gusty northwesterly winds develop Monday morning and
  afternoon.

VFR with generally SKC conditions will prevail this afternoon,
with some additional cumulus development possible late in the
day. Northwesterly winds gusting up to 25 kts will diminish this
evening and turn southwesterly.

A fast-moving wave will bring scattered showers to the region
late this evening/early overnight. Have converted the inherited
PROB30 groups to TEMPOs for all sites except GYY with this
issuance given model trends. Depending on how robust showers
remain, can`t rule out some 30 knot wind gusts as this activity
rolls across the terminals.

Thereafter, MVFR stratus will develop but should lift to VFR
through late Monday morning. Northwesterly wind gusts will also
develop quickly through this time as well, with gusts in the mid
20 kt range expected through the afternoon. There is a small
chance that a few light sprinkles develop Monday afternoon, but
these chances remain pretty low at this point.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 1 PM CDT this afternoon for
     Winthrop Harbor IL to Gary IN.

     Small Craft Advisory until 4 PM CDT this afternoon for Gary to
     Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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