textproduct: Chicago

KEY MESSAGES

- Gusty south-southwest winds to 35-40 mph will persist through this evening.

- Mild conditions with periods of showers and some storms through Friday, then again from late weekend into early next week.

- Combined rainfall amounts tonight through Friday may exceed an inch across portions of the forecast area. This could produce new rises on area rivers and creeks.

DISCUSSION

Issued at 239 PM CDT Wed Apr 8 2026

A stacked low pressure system continues to drift across the Canadian- ND border and will be moving into the northern Great Lakes tonight. Stretching from this low across southern MN, northwest IA, and eastern NE is a cold front that will be moving into northern IL (and eventually northwest IN) late this evening and overnight. Current regional radar does show some spotty echoes along and just ahead of the cold front in IA and MN but precipitation does not appear to be reaching the ground presently. However, as the front continues to approach the coverage of rain showers should increase with the potential for a few embedded thunderstorms to develop as well. Given that instability profiles continue to look rather modest have opted to keep a low (10-15%) chance for thunder in the forecast, but suspect many will just see showers tonight. That said, as the front progresses across our area the coverage of showers (and any storms) should diminish as the front encounters drier air with southward extent. Thus, there is a good chance that those south of the Kankakee River Valley could remain rain-free tonight. Regardless, mild temperatures in the low to mid-50s are expected tonight with some occasional southwesterly wind gusts around 20-25 mph.

Heading into Thursday, the front will begin to stall near (or just south of) the I-80 corridor. Due to the more limited moisture and weaker forcing atop the front, dry conditions are expected for Thursday morning. Though, another shortwave impulse will be ejecting out of the central Plains Thursday afternoon which should be able to regenerate at least some isolated to widely scattered showers and thunderstorms along and just south of the stalled frontal boundary. While forecast soundings do show around 30-35 kts of bulk shear to be present Thursday afternoon, the modest instability (around 300- 500 J/kg) looks to limit storm organization and keep the threat for any severe weather low. Otherwise, expect another warm afternoon with highs once again in the mid to upper 60s. Though some locations south of the front could get into the lower 70s if skies clear enough.

In addition to the aforementioned shortwave impulse Thursday afternoon, a broader shortwave trough is expected to be diving out of the northern Plains Thursday night. This trough should provide much better forcing and allow for a broader coverage of showers and embedded thunderstorms to develop across northern IL and northwest IN through the night. Since the frontal boundary will be very slow moving during this time and storm motions are forecast to be nearly parallel to the boundary, conditions continue to look favorable for training showers and thunderstorms. As a result guidance is in good agreement that a swath of 0.5-1.0 inch rain amounts will materialize over portions of northern IL and/or northwest IN Thursday night with a 20-30% chance for localized amounts in excess of an inch. While the exact location of these heaviest rain amounts is still uncertainty due to the convective nature, the already saturated ground and elevated rivers won't take much to get flooding issues to develop. Therefore, we will be watching trends closely and may need to consider a Flood Watch if confidence on the 1+ inch amounts grows. In the meantime make sure you keep checking back for forecast updates and ensure you have ways to receive flood alerts should they be issued especially if you live near area rivers.

The front is expected to begin to slowly move into the Ohio River Valley on Friday which should allow for rain to taper from northwest to southeast by Friday evening. In the wake of the front, more seasonable temperatures can be expected with highs in the mid to upper 50s Friday afternoon inland with highs in the 40s near the lake. Mid-level ridging will move into the Great Lakes Friday nigh and persist through at least Saturday evening keeping dry conditions in play for the first part of the weekend. However, the persistent east-northeast winds don't look to allow temperatures to improve much Saturday with highs once again forecast to be in the mid-50s to lower 60s inland with 40s expected near the lake.

While we enjoy a break in the active weather, upper-level troughing (comprised of several shortwaves) is forecast to develop across the western CONUS this weekend. By Saturday night one of these shortwaves is projected to break off the main trough and traverse from the central Plains into the upper Mississippi Valley. Guidance continues to indicate that as this shortwave nears the Mississippi river a plume of showers and thunderstorms should develop ahead of it and ride the western periphery of the aforementioned ridge. This trajectory favors most of the showers/storms to occur in IA and southern WI, but give the close proximity to us cannot completely rule out a few shower/storms brushing the northwest portion IL. At this time have opted not to change the 20-40% POPs offered by WPC and the NBM but suspect these are a bit broad and may need to get trimmed if trends continue.

Regardless of what happens Saturday night, the ridge should begin to get pushed east by yet another shortwave that is forecast to eject across the central Plains on Sunday. This next shortwave will also lead to the development of additional showers and thunderstorms on which could arrive in our area as early as Sunday afternoon/evening. However, timing on when exactly this next round of rain arrives continues to be very uncertain in latest ensemble guidance and thus confidence is low. That said, it does look that a stormy period of weather will be in play for us during the Sunday through Tuesday timeframe so be sure to stay tuned.

Yack

AVIATION /06Z TAFS THROUGH 12Z FRIDAY/

Issued at 1230 AM CDT Thu Apr 9 2026

Key messages:

- Strong southwest wind gusts prevail through around 09Z. Despite these gusts, low level wind shear is also possible.

- Intermittent showers are possible through daybreak. A drier afternoon before a front lifts and provides more widespread rain to the region

- Wind shift to the northeast late this afternoon.

Two broken lines of showers are slowly moving east ahead of a front early this morning. No lower cigs or vis restrictions are being observed. There is low confidence in the timing of the showers at terminals but intermittent periods of showers are possible through daybreak. More impactful are the strong and gusty southwest winds. Winds were still gusting locally to 30 knots at the time this discussion was sent, however, obs west of the initial band of showers have already lost there gustiness. That being said, winds 2000-3000 ft AGL remain over 50 knots (analyzed by the KLOT radar). Low level wind shear remains a threat through around 09Z, even with strong wind gusts at the surface.

Showers will gradually taper off after sunrise and winds remaining around 10 knots and out of the west (if not the just north of west for a brief period. VFR conditions are expected through the day, but it will be only a brief respite. The front moving through the area currently will stall for a moment south of the area and then lift northward late this afternoon. There is a chance for showers late afternoon ahead of the front, but there are better chances for widespread rain with the front after 03Z (and really closer to 06Z). Last but not least, models continue to project a lake breeze flipping winds to the northeast tomorrow afternoon. Given that this is occurring as the front is starting to move northward, there is lower confidence in exact wind trends at the end of the TAF period. However, the consistent signal in models switching winds to the northeast provided enough confidence for inclusion in the TAF.

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 4 AM CDT early this morning for the IL nearshore waters.

Small Craft Advisory until 7 AM CDT this morning for the IN nearshore waters.