textproduct: Chicago

KEY MESSAGES

- Mild weather continues this evening, but a cold frontal passage early Sunday morning will result in blustery and sharply colder and cloudy conditions for Sunday.

- Cooler weather persists on Monday, before temperatures moderate into midweek.

DISCUSSION

Issued at 200 PM CDT Sat Mar 21 2026

Mid and high level cloud cover will continue to clear the area this afternoon, fostering a mainly sunny afternoon. Temperatures this afternoon will top out well into the 70s, if not the low 80s (in some areas) as breezy southwesterly low-level flow develops in response to the compact surface low tracking into northern WI. Conditions will also warm through the afternoon along the Lake Michigan shore as the flow shifts southwesterly.

These unseasonably mild conditions will persist tonight, but will come to a quick end early Sunday morning as a strong cold front drops south across the area. In advance of this front, temperatures will hover in the upper 50s to the low 60s for most of tonight. However, with the frontal passage around, or a bit before daybreak Sunday morning, a much colder low-level airmass will be driven in off of Lake Michigan on gusty (30-35 mph) north-northeasterly winds. The result will be quickly falling temperatures into the 40s Sunday morning (afternoon) along and north (south) of the Illinois and Kankakee rivers. Once temperatures do drop, do not expect much if any recovery Sunday afternoon. In fact, the presence of a continual feed of colder air off of Lake Michigan along with an extensive post frontal low-level status deck will hold temperatures fairly steady in the 40s Sunday afternoon (low 40s near the lake). The possibility also exists for some scattered post frontal showers during the day.

The cooler weather will persist on Monday as a surface high shifts into the western Great Lakes. Accordingly, high temperatures are generally expected to be in the 40s (coolest near the lake). The main differences from Sunday's weather will be the lighter northeasterly winds and less cloud cover for the day Monday.

Broad WNW mid and upper-level flow will take hold across the region next week. This will result in a series of weather disturbances and associated surface cold fronts crossing the Great Lakes region during the middle and later part of next week. In advance of these fronts, conditions will warm back well into the 50s on southwesterly low-level winds on Tuesday. Thereafter, mild weather does look to persist to some degree for Wednesday and Thursday. However, a couple of cold fronts may shift into the area. The first may shift into northern parts of the area on Wednesday before stalling just south of the lake. If this occurs, onshore flow north of the boundary would be likely to promote cooler conditions than currently forecast for Wednesday, particularly across northeastern IL. Otherwise, temperatures could easily make a run back around 60F for Wednesday. Thursday could then end up being the warmest day next week as a low-level thermal ridge advects over the area in advance of the next approaching cold front. This second cold front looks to be more substantial than Wednesday's. Accordingly, temperatures are expected to trend back down into the 40s and low 50s on breezy northeasterly winds at the end of the week.

Generally dry weather is expected through the period, with only some low (20-30%) chances of precipitation Sunday, and again Thursday.

KJB

AVIATION /00Z TAFS THROUGH 06Z MONDAY/

Issued at 627 PM CDT Sat Mar 21 2026

Key aviation forecast messages for the 00Z TAFs:

- Breezy southwest winds diminish early this evening, with a period of LLWS late as a 45 kt WSW low level jet develops aloft.

- Cold front pushes across the terminals early Sunday morning with a wind shift to the NNE and blustery conditions with gusts 25-30 kt through much of the day/evening.

- Brief period of IFR cigs possible behind the front early Sunday, then MVFR stratus lingers through the end of the period. Can't rule out some patchy DZ/-RA, though looks to be minimal.

Surface low pressure was over far northern WI at 6 PM, trailing a cold front across southern MN into NE. Breezy southwest winds ahead of the front was gusting into the 20-25 kt range at issuance time, but should ease with sunset. A period of LLWS is likely later this evening/early overnight however, as a WSW 45 kt low level jet shifts across the area, weakening quickly predawn Sunday. The aforementioned cold front is expected to push south across the terminals around daybreak Sunday morning, with a sharp wind shift to the NNE. These winds will become blustery with gusts 25-30 kts by midday and persisting into Sunday night before slowly diminishing.

VFR conditions will persist ahead of the cold front, after which low clouds will spread into the region on those NNE winds. There looks to be a period of at least SCT/occasional BKN IFR for a few hours into late morning before cloud bases rise into low-end MVFR which looks to linger through the rest of the period. Can't rule out some patchy drizzle at times especially later in the afternoon, although the profile becomes fairly dry save for the low level MVFR cloud layer. Would expect any precip to be light and patchy, and have not included in TAFs.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory from 7 AM Sunday to 1 PM CDT Monday for the IL nearshore waters.

Small Craft Advisory from 10 AM Sunday to 4 PM CDT Monday for the IN nearshore waters.