textproduct: Chicago

KEY MESSAGES

- Waves of showers and thunderstorms may occur on Sunday. There is a Level 2 out of 5 threat for severe thunderstorms Sunday afternoon mainly east of Interstate 55. The primary threat is damaging winds.

- A period of accumulating snow accompanied by northwesterly winds gusting over 40 mph may occur Sunday night into early Monday, mainly northwest of Interstate 55.

- A period of cold temperatures is expected Monday and Tuesday, with overnight wind chills ranging from 5 to 15 below, especially Tuesday morning.

- The period of cold temperatures should be brief with warming temperatures by the end of next week.

DISCUSSION

Issued at 304 PM CDT Sat Mar 14 2026

Through Monday:

Forecast concerns continue to focus on the significant storm system taking shape across the front range of the CO Rockies this evening.

Lee cyclogenesis is slatted to occur this evening over the central High Plains in response to a rapidly amplifying upper- level shortwave diving southeastward across the central United States. Ensemble model guidance remains in excellent agreement in tracking the surface cyclone eastward across the mid-Missouri Valley late tonight, then along or just south of the Illinois/Wisconsin state line Sunday afternoon. Thereafter, strengthening upper level diffluence ahead of the approaching negatively tilted mid- level trough will foster a rapid deepening of the low (to near 980 mb) as it lifts northward across lower Michigan Monday afternoon.

This storm system will produce several hazardous weather threats across our area Sunday into Monday. These include:

- Thunderstorms on Sunday, some possibly strong in the afternoon and early evening. - Strong gusty south winds on Sunday, strongest southeast of I-55, where a wind advisory is in effect. - Turning much colder and very windy from the northwest Sunday evening into Monday. - Rain mixing with a brief period of sleet and freezing rain before transitioning to snow from west to east across the area Sunday evening and night.

Storm and Severe Threat Sunday:

At least a couple of waves of showers and thunderstorms are expected on Sunday. The first period favorable for mainly elevated storms will be during the morning hours of Sunday. Steep mid- level lapse rates could support the possibility for small hail with these storms. However, poor effective storm layer shear <25 kt suggests that organized severe storms are not likely with this initial morning round of storms.

Later in the day, particularly from mid to late afternoon into the early evening hours, the main storm system will be shifting across far northern IL. As it does, intensifying low-level winds (60+ kt at 850 mb) will foster a strongly sheared kinematic environment in advance of the eastward shifting cold front. In spite of this, the likely presence of low clouds in the warm sector through the day and only modest near surface moisture (dewpoints in the low 50s) is expected to stunt destabilization ahead of the approaching front. Nevertheless, strong convergence and forced ascent along the cold frontal boundary should still be able to support a forced line of shallow convection as it sweeps eastward across the area late in the day into the early evening. The primarily threat with this activity will be strong damaging wind gusts in excess of 60 mph.

Strong Non-Thunderstorm Winds Sunday:

Outside of the thunderstorms on Sunday, conditions are expected to become very windy through the day, particularly across southern sections of the area, where a Wind Advisory is in effect. Increasing southerly winds, driven by rapid pressure falls in advance of the approaching surface low, are expected to result in gusts of 45, to perhaps briefly as high as 55 mph in the afternoon and early evening. The presence of lower cloud cover may limit the overall magnitude of the gusts to some extent. Because of this, in collaboration with neighboring offices, we have opted to convert the High Wind Watch to a Wind Advisory for Sunday into early Sunday evening. It is possible that this advisory need to be expanded a bit farther north with later forecast updates.

Winter Weather Threat Sunday night into Monday:

Rain will transition over the snow from west to east Sunday evening as a much colder airmass quickly spills in across the area along the backside of the deepening surface low moving into Lower Michigan. While a short hour or so period of mixed precipitation looks plausible, the main concern will the shift to accumulating snow in the presence of increasingly gusty northwesterly winds Sunday night into Monday morning. There continues to be some differences amongst guidance in terms as to how much additional moisture will fall as snow in the deformation band of the cyclone into Monday morning. However, given the expected track of the system, forecast thinking continues to favor the heaviest snow axis from northwestern IL into WI, with much lighter amounts with east-southeastward extent across our area. This results in general forecast snow amounts in the 2 to 5 inch range in my far northwest (near the Rockford area), dropping to only an inch or two across the Chicago area and points southeast.

Snowfall totals will not really be the main story with this wintry weather event. Really, the combination of falling snow with blowing snow on gusty northwest winds (45+ mph gusts) will be the primary concern locally with this event. While the snow character will start quite wet with a ratio near 10:1, which may initially limit accumulations on the wet/road ground, rapidly falling temperatures through the column will support a more fluffy (more blowable) snow late Sunday night into Monday. With this in mind, conditions should become more hazardous with time Sunday night, with the potential for periods of near blizzard conditions at times, particularly across the more open areas of northern/northwestern IL. These poor conditions are expected to continue into Monday morning before the snow gradually tapers off from south to north through the day on Monday.

No changes have been made to going Winter Storm Watch across the Rockford area, owing to the fact that potential warning level impacts will not onset here until sometime later Sunday evening. We do envision that this gets transitioned to either a warning or an advisory as we get closer to the event. Winter Weather Advisory conditions could also expand east-southeast of the current watch area due to the combination of poor visibility in snow and blowing snow through Monday morning.

KJB

Monday Night through Saturday:

The low pressure system providing Monday's weather will continue to move east allowing for drier conditions over the region. 850 mb temperatures are expected to drop down around -20C overnight into Tuesday morning. Even as winds generally will be subsiding through the overnight, they are expected to remain breezy enough to drop wind chill values down to between -5 to -15F.

As a strong upper level ridge is expected to grow over the desert south west, weak northwest flow is forecast to remain over the western Great Lakes. There is still good agreement of another upper level shortwave embedded in the flow to pass over the area late Tuesday into Wednesday morning. This could provide another quick shot of some snowflakes to the area. But as the previously mentioned ridge expands through the week, temperatures are expected to rise into the 50s and possibly low 60s by the end of the work week with drier conditions.

DK

AVIATION /18Z TAFS THROUGH 00Z MONDAY/

Issued at 1227 PM CDT Sat Mar 14 2026

Key Aviation Messages for the current TAF period:

- Low level wind shear overnight, despite southeasterly wind gusts over 20 knots

- Southwesterly wind gusts in excess of 30 knots are expected tomorrow

- Waves of showers and thunderstorms at terminals tomorrow late morning through early evening.

VFR conditions continue with easterly winds around 10 knots today. While KDBQ did have a brief period of some snow flakes this morning, drier air near the surface should prevent anything from falling at the terminals. While a few flurries this afternoon cannot be completely ruled out, it was kept out of the TAF.

The low level wind field will increase around and after midnight. Even with southeasterly surface wind gusts over 20 knots, a low level jet in around 50 knots will keep low level wind shear mentioned in the TAF through and just after daybreak. Winds will turn to the south after sunrise with gusts increasing to near 30 knots.

An area of surface low pressure will move across Iowa tomorrow morning and deepen as it passes over northern Illinois in the afternoon. Scattered showers and thunderstorms are expected late morning/early afternoon. The PROB30 was kept in the TAF currently due to the uncertainty in the coverage of thunder during this time window, though there will be potential breaks in the showers/thunder. However, guidance is in pretty decent agreement of a cold front, associated with the surface low, pushing through in the late afternoon. While there is still some uncertainty in the exact timing of the front, it looks like this window has the better coverage of showers late in the afternoon/early evening. The chances for thunder appears better south of the Chicago terminals. With a more limited threat, it was kept out of the TAF for now, but will be re-evaluated. Cold air will filter in and change the precipitation type from rain to snow, but that looks to be outside the current TAF period.

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...Winter Storm Watch from Sunday evening through Monday evening for ILZ003-ILZ004-ILZ008-ILZ010.

Wind Advisory from 10 AM to 9 PM CDT Sunday for ILZ023-ILZ032- ILZ033-ILZ039-ILZ108.

IN...Wind Advisory from 10 AM CDT /11 AM EDT/ to 9 PM CDT /10 PM EDT/ Sunday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Gale Watch from Sunday morning through Sunday evening for the IL and IN nearshore waters.