textproduct: Chicago

KEY MESSAGES

- Showers and storms along a passing cold front are expected through the morning, exiting to the east by the afternoon

- Colder and drier conditions are expected through the early part of next week.

- Temperatures warm up again toward the tail end of next week, but it comes with another chance of precipitation.

DISCUSSION

Issued at 226 AM CDT Sat Apr 4 2026

Recent SPC mesoanalysis depicts an area of surface low pressure in northeastern Iowa at the time this discussion was published. That low is projected to continue a east-northeast track toward the northern Great Lakes and Ontario thereafter. Yesterday's warm front appears to have stalled south of the forecast area, prompting nudging minimum temperatures downwards for this morning for the cooler air mass that remains north of it. No matter, a surface cold front in connection with the previously mentioned low will sweep across the region this morning. The showers and thunderstorms that are presently along and ahead of it crossing the Mississippi will continue to move eastward through the morning. The severe threat with these storms appears fairly low. There is technically a risk for localized gusty winds with them, but the better well of DCAPE looks closer to the warm front, south of the forecast area. The bigger concern would be from localized downpours over already saturated soils. Recent MRMS data has inch per hour rain along the front, with localized spots up to 2 inches per hour. While the front is progressive, it is only moving at around 25 to 30 mph. An Areal Flood Warning was issued for the areas that received the most precipitation last night, but a Flood Watch remains in place for the rest of the forecast area through 10 AM this morning.

The front should be over northwest Indiana by mid-morning and continuing to move east away from the area through the afternoon. A stray lingering shower may be possible in the afternoon as it pulls away, but drier conditions are expected later today. Winds will turn to the west behind the front, and will become breezy. As a low level jet strengthens tonight, model soundings continue to show mixing into the 40 knot winds at the top of the channel, which can result in gusts over 30 mph through the overnight tonight. Lastly, high res guidance is picking up on a mid level short wave wrapping around a larger upper level trough tonight over Wisconsin. Guidance has shown little agreement on whether or not any sprinkles or a brief light rain would develop. It appears that the better forcing would be farther north in Wisconsin, and with a lack of deep moisture in soundings, confidence is low in precipitation. It was decided to throw some "silent PoPs" (between 10 to 15 percent chance) for the northern tier of counties along the Wisconsin border.

Another short wave trough is expected to drop southward out of Canada on Sunday, sending yet another cold front across the area that night. Models are suggesting that this front will be a little more moisture starved than today's front, but still enough for recent models to suggest a slight chance (20 percent or less) for a passing shower - though most of the area will remain dry. More impressively with this front will be it ushering in a much colder air mass in its wake. 850 mb temperatures drop down below freezing on Monday morning, and down near -10C by Tuesday morning. Our recent stretch of temperatures in the 50s and 60s (or higher) probably makes us forget that having low temperatures in the 30s is quite seasonable. But the reminder will arrive Monday morning, with low temperatures in the 20s expected on Tuesday morning. Luckily, considering how April weather can change fairly quickly, it will not be a permanent cold snap.

An upper level ridge is expected to develop in the middle up next week. As the ridge grows, afternoon high temperatures will warm up once again into the 50s and 60s, maybe even low 70s by the end of next week. Long range guidance is projecting another upper level trough to move over the northern Plains and Great Lakes from Wednesday night into the end of next week and potentially another one entering next weekend. There will likely be breaks in the rain, but after a quieter stretch of precipitation, it looks like a wetter pattern may return by the end of next week.

DK

AVIATION /12Z TAFS THROUGH 18Z SUNDAY/

Issued at 633 AM CDT Sat Apr 4 2026

Aviation weather concerns for the 12Z TAFs:

- Period of SHRA/RA through about mid-morning (late morning at GYY). Exception is at RFD where SHRA are winding down. Only TS threat appears to be south/east of GYY early this AM.

- Period of LIFR ceilings and IFR/MVFR vis appears likely this morning as surface low/cold front move through. Conditions should improve to MVFR cigs/VFR vis by mid-late morning.

- Messy wind field early with low/front moving through. Should favor a ESE-SSE direction early, shifting quickly WSW and becoming gusty 25-30 kts this morning through remainder of TAF period.

Surface low pressure center will track along the IL/WI border this morning, with an occluding warm/cold frontal system moving across the terminals. From a wind perspective, this will result in southeast to south-southeast winds early, shifting quickly to the west-southwest and becoming gusty as the front moves through this morning. Winds will then remain generally WSW-W with gusts 25-30 kts for much of the remainder of the TAFs. It's possible some gusts in excess of 30 kts could occur late today into this evening, though confidence is somewhat low in these higher speeds.

Otherwise, an area of rain/showers will continue to move east across the area this morning, ending from the west after the cold front moves through. Thunderstorm coverage has really waned this morning, and am not expecting TS other than south/east of GYY. Perhaps more impactful will be the likelihood for a period of low stratus (LIFR/IFR) to develop this morning with ceilings as low as 200-400 ft and some 2-4SM visibilities in fog through about mid-morning. Conditions should improve late this morning/midday however, as drier low-level air spreads in on those gusty westerly winds. Slowly rising MVFR ceilings are then expected through the period, though can't rule out improvement (at least temporarily) to VFR late today/this evening.

Ratzer

LOT WATCHES/WARNINGS/ADVISORIES

IL...Flood Watch until 10 AM CDT this morning for ILZ013-ILZ021- ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-ILZ106- ILZ107-ILZ108.

IN...Flood Watch until 10 AM CDT /11 AM EDT/ this morning for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 10 AM this morning to 10 AM CDT Sunday for the IL and IN nearshore waters.