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 /00Z TAFS THROUGH 06Z SATURDAY/

Issued at 718 PM CDT Thu Apr 23 2026

Key Messages:

- Low-level wind shear is possible at times tonight.

- There remains a 30-50% chance for thunderstorms tonight, highest chances at RFD.

- Additional showery periods are possible during the daytime tomorrow.

- MVFR ceilings are likely tomorrow morning.

A low-level jet stationed over the area will strengthen to around 40-45 kts at 2000 ft AGL this evening. Marginal low- level wind shear may thus be observed for a period of time tonight wherever gusts cease and sustained winds subside under 10 kts (most likely at GYY, DPA, and RFD).

A line of storms will approach the area from the west later tonight, though it will be on a weakening trend. RFD stands the best chance to see lightning and could also see a brief period of showers a few hours before the main line of decaying storms arrives. For the Chicago metro terminals, the overall chances for lightning are lower than at RFD, but still appear to be appropriately conveyed by the inherited PROB30 groups for TSRA in the respective TAFs. Despite being in a decaying state, the incoming line of convection may still produce a gusty westerly wind shift and gusts in the 30-40 kt range as it rolls through the area. Shower coverage should then diminish towards daybreak, though at least isolated showers will remain possible through the morning hours while MVFR ceilings likely filter into the area.

Isolated to scattered showers may redevelop closer to an incoming cold front during the afternoon tomorrow. Questions about the quality of available low-level moisture and the degree of diurnal destabilization with the morning cloud cover remain, but there appears to be enough support in high-resolution model guidance to at least warrant a PROB30 group for SHRA at all of our TAF sites. In the worst case, a few isolated thunderstorms may develop in the advertised PROB30 windows, but did not have enough confidence in TSRA occurring to warrant a formal mention of that in the TAFs at this time. The shower/storm potential should end and winds will shift to a northwesterly direction behind the cold front after it moves through tomorrow afternoon.

Ogorek

LOT WATCHES/WARNINGS/ADVISORIES

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