textproduct: Chicago

KEY MESSAGES

- Periods of showers and/or drizzle are expected at times from later today through this weekend (greatest chances/coverage expected tonight night through Saturday morning).

- Additional periods of wet weather are likely next week.

DISCUSSION

Issued at 215 AM CDT Fri Oct 30 2026

The surface cold front which pushed southeast across the forecast area on Thursday has settled well south of the area across central IL/IN early this morning. Skies have cleared across the forecast area in the wake of the front, though boundary layer decoupling has allowed for decent radiational cooling conditions overnight which has led to some fog development over portions of northwest IN. Some dense fog is evident in surface obs mainly near/southeast of the Kankakee River, though this may be somewhat limited in time/space early this morning as a slight increase in modest north-northwest winds and some gradual advection of drier low-level air is expected. For now have issued a Special Weather Statement for a few hours parts of northwest IN south of the Kankakee River, and will continue to monitor.

Attention then turns to a mid-level short wave trough currently across New Mexico and western Texas, which is progged to lift slowly northeast across the lower Missouri and mid-Mississippi Valleys into Saturday. This is expected to induce southerly return flow atop the northward-sloping frontal zone, with attendant warm/moist advection resulting in eventual development of elevated showers across the forecast area. Spotty showers/sprinkles are possible as early as this afternoon across our IL CWA (especially west), with the greatest coverage likely from later tonight through Saturday morning. This is as the elevated (~850 mb) warm front lifts into the area beneath a region of upper-level divergence associated with the right entrance region of a 100+ kt jet streak over the northern/eastern Great Lakes.

Some of the WRF/ARW guidance depicts some weak elevated MUCAPE late tonight in a somewhat steep mid-level lapse rate regime across our far western cwa (I-39 corridor westward). While an isolated rumble can't be ruled out, any thunder coverage looks to be quite limited. Guidance is in general agreement in shower coverage decreasing Saturday afternoon and evening for trick-or- treat time, though the presence of the dampening short wave and the low-level baroclinic zone and fairly moist profiles will likely make for some lingering light showers or sprinkles at times into the evening. In fact mostly cloudy, drizzly or sprinkly weather may continue through the night. Temperatures will remain relatively mild for the end of October, with highs in the upper 50s/60s and lows in the 40s and lower 50s.

A second short wave trough (currently off the southern California and northern Baja coast) is progged to lift northeast across the area on Sunday/Sunday night, with another uptick in shower coverage likely especially across our southeastern cwa and downstate IL/IN. Heading into early next week, ensemble guidance is in decent agreement in shifting the long-wave western CONUS upper trough slowly eastward, with a significant surface low pressure system moving into the region by mid-week. Considerable spread remains in these solutions at this distance however, with respect to individual short waves embedded within the larger scale trough and the depth, placement and timing of the associated surface features. The main takeaway at this time is that additional periods of unsettled weather are likely. Temperatures, while currently looking to remain above average through mid-week, will also depend on the location of surface low/frontal feature placement. A trend toward seasonably cooler weather would likely develop toward/just beyond the end of this forecast cycle in the wake of the deep, amplified system.

Ratzer

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 632 AM CDT Fri Oct 30 2026

Main Item of Note:

- Potential for periodic MVFR VSBY and perhaps MVFR CIGs Saturday morning in higher rainfall rates

Showers approaching the MS River this morning are expected to erode/weaken farther east in the ZAU airspace this afternoon. Some non-impactful sprinkles may reach the ground, though continued to defer any formal mention in the TAFs to subsequent updates. As another disturbance approaches tonight, shower coverage will gradually increase in the late evening and overnight, earliest at RFD. Embedded higher rainfall rates appear plausible at times per model forecast soundings, from the pre-dawn hours of Saturday until about midday.

Light north to northeast winds to start today will increase in speed by mid morning, with east-northeast directions this afternoon-early evening, and then east-southeast tonight into Saturday morning.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

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