textproduct: Chicago

KEY MESSAGES

- Period of showers and scattered thunderstorms with a cold front tonight into Friday.

- Seasonable and dry conditions over the weekend.

- Threat of showers and thunderstorm return Monday, as does the threat of severe weather and heavy rainfall.

DISCUSSION

Issued at 224 PM CDT Thu Apr 23 2026

All is quiet across our region this afternoon. However, well west of our area (across the Mid-Missouri Valley) a line of thunderstorms will continue to develop and mature in advance of an eastward shifting cold front through the remainder of the afternoon. The airmass in which these storms develop will favor organized severe thunderstorms into this evening with eastward extent across much of IA southwestward into eastern KS and western MO. Fortunately, this line of storms is expected to weaken with eastward extent tonight as nocturnal stabilization of the boundary layer occurs overnight. Accordingly, it appears the severe threat will be fairly low across much of northern IL into northwestern IN. However, lingering outflow from this line of decaying line of storms could still produce a brief period of gusty winds up to 50 mph, particularly west of the Fox Valley and Illinois River Valley. Rainfall rates and amounts are also expected to be waning with this activity overnight, so we currently do not anticipate any worsening of the ongoing river flooding.

Lightning and thunder activity will be on a diminishing trend into early Friday morning as the remnant showers shift across northeastern IL and northwestern IN in advance of the approaching cold front. While extensive cloud cover through the morning will limit destabilization in advance of this front, cooling mid-level temperatures associated with the incoming mid- level short-wave does look to support steepening low-to-mid level lapse rates by midday/early afternoon. Accordingly, it appears some renewed widely scattered showers and storms will occur with, and just ahead of, the cold front into early Friday afternoon. The most favored areas for this new development looks to be generally along and east of the I-55 corridor. Fortunately, limited instability and shear looks to curtail the threat for more organized severe storms. Otherwise, expect the threat of showers and storms to end from northwest to southeast through the afternoon.

Cooler, but pleasant weather conditions are expected through the weekend in the wake of Friday's cold frontal passage. Expect inland temperatures to range from the upper 60s to low 70s. However, closer to Lake Michigan, onshore east-northeasterly winds will keep conditions cooler, with highs generally in the 50s to low 60s.

Following a quiet weekend weather wise in our neck of the woods, a significant mid-level impulse (and upper-level speed max) coming onshore across southern CA late Saturday, is forecast to eject east-northeastward across the Rockies by late Sunday. This will set the stage for lee cyclogenesis and the development of a northeastward tracking notable sub-995 mb low from the central Plains somewhere up across the upper Midwest into early next week. While ensemble spread with the exact surface low track across the Upper Midwest on Monday remains, conceptually a strong surface low tracking northwest of area during the afternoon and evening hours in late April certainly adds increased concern for the threat of severe weather and heavy rainfall in or very near our area. Accordingly, Monday will be a day we will have to watch closely for both a heavy rain and a severe weather threat.

In the wake of the Monday system, a period of cooler and drier weather should set up for the middle of next week.

KJB

AVIATION /18Z TAFS THROUGH 00Z SATURDAY/

Issued at 1249 PM CDT Thu Apr 23 2026

VFR conditions are expected into at least this evening. SSW/S winds will gust up to 25 knots for the Chicago terminals and possibly up to 30 knots for RFD through sunset. A developing 45 knot low-level jet will lead to marginal LLWS at RFD/DPA/GYY this evening, with S gusts over 20 knots precluding the need for LLWS at ORD/MDW.

An extensive line of convection is expected to develop from Kansas to southern Minnesota late this afternoon. This convection should remain strong to severe across Iowa and northern Missouri well into this evening before quickly weakening with eastward extent across Illinois overnight. TS potential remains around 30 percent or less for the Chicago terminals, while some widely isolated TS may survive far enough east to affect RFD. A few SHRA may also precede the main line at RFD by a few hours late this evening. Any TS or SHRA is capable of producing strong outflow with gusts up to 40 knots.

SHRA coverage will diminish prior to sunrise and become weak and quite sparse Friday morning. A period of MVFR ceilings are likely to develop during this time while winds settle SW around 10 knots.

A cold front will cross the terminals mid to late Friday afternoon. A few isolated SHRA or perhaps a brief TS cannot be ruled out along and ahead of the front, but low-level moisture may be insufficient to generate deeper cumulus during this time. Opted to keep the TAFs dry after 18Z, with SHRA/TS potential around 10% roughly 19-21Z.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.