textproduct: Chicago

KEY MESSAGES

- Accumulating snow is expected late this afternoon into this evening, with slippery travel conditions expected.

- A strong arctic cold front will move across the area late this evening with west northwest winds gusting to 40 mph. Some blowing snow will be possible.

- Bitterly cold conditions are expected late tonight through Tuesday morning with wind chills 15 below to 25 below zero expected Monday morning.

- A clipper system may bring accumulating snow to parts of the area Tuesday night into Wednesday morning.

DISCUSSION

Issued at 220 AM CST Sun Jan 18 2026

A strong arctic cold front will move across the area late this evening into the early overnight hours. Ahead of this front, a period of snow is expected to spread across the area starting in the late afternoon and continuing through mid/late evening, with the focus for snow along and north of a LaSalle to Rensselaer line. Unlike the system Saturday evening that was expected and did weaken as it moved across the area, this system will likely continue producing snow as moves across the entire area and with the dry/cold airmass in place, fluffy dry snow may result in an inch of snow accumulation, perhaps 1-2 inches across parts of northeast IL. The accumulating snow looks to end as the cold front arrives but there may still be a period of flurries or snow showers into the early overnight hours.

Winds behind the cold front will quickly increase into the 20-30 mph range with gusts 35-40 mph possible. Its unclear how much blowing snow may occur with the expectation that most, if not all the falling snow will be over. More likely is low drifting snow, presenting issues for north/south roads in open areas. Opted not to include any blowing snow in the forecast/grids, but this will need to be looked at again with later forecasts.

High temps today may struggle to reach 20, hold steady for a few hours during the snow, then steadily fall behind the front with low temps by daybreak Monday morning around zero or a few degrees below zero across the northwest cwa, to the low single digits for the rest of the area. With winds still expected to be in the 20-25 mph range, with higher gusts, this will allow wind chills in the 20 below to 25 below range for most of our IL counties. Wind chills for Chicago and along/east of I-57 may be more in the 15 below to 20 below zero range. Opted to draw the boundary for the cold weather advisory along the IL/IN state line, though as noted, marginal criteria on the far eastern edge of the advisory. High temps Monday only rebound into the mid/upper single digits for most areas, perhaps some low teens across central IL. Wind chills are expected to remain below zero all day Monday, Monday night and into Tuesday morning. Similar low temps are expected again Tuesday morning, but with lower wind speeds, wind chills look to be in the 10 below to 15 below range.

One change to the forecast that will need to be watched is another weak wave that moves across the region late Monday afternoon into Monday evening. Models are dry with this feature, as is the blended guidance, but if this materializes in the very cold airmass, there may at least be some flurries.

Models remain in overall good agreement with a clipper system for Tuesday night into early Wednesday morning with a chance for accumulating snow across at least far northern IL. Still a few days away and snow location/amounts will be dependent on the exact track, but overall, this has been a well handled feature among the models for several days. Another feature of note is a cold front late Wednesday or Wednesday night, that may bring another period of flurries or snow showers.

Temps still look to briefly moderate Wednesday, ahead of the clipper system when highs may reach the upper 20s/lower 30s.

There remains quite a bit of uncertainty for the end of the week into the weekend with the potential for an active pattern for or near the local area. The ensembles seem to be in a little better agreement for precipitation chances for the local area, but there is still a decent spread in possibilities. Regardless of whether precip develops for the local area, current trends continue to favor a cold/very cold pattern. cms

AVIATION /12Z TAFS THROUGH 18Z MONDAY/

Issued at 609 AM CST Sun Jan 18 2026

- Another period of snow later this afternoon through the evening with associated MVFR VSBYs/CIGs, occasional IFR VSBYs.

- Strong winds (gusts 30-35 kt) arrive behind cold front overnight which could lead to shallow blowing/drifting snow.

Mainly VFR conditions are expected through early afternoon with scattered to briefly broken MVFR clouds around which could produce a few non-accumulating flurries through mid morning.

No major changes in thinking for the snowfall potential later this afternoon through the evening. Can't rule out dry air delaying the onset of the steadier snowfall by an hour or so, but made no changes to the 21-23Z timing with this update for now. Expect prevailing MVFR CIGs and VSBYs with occasional dips to IFR (1-2SM), mainly in the early evening, with amounts around 1 inch. The snow may transition over to scattered snow showers or flurries through the rest of the overnight hours paired with shallow blowing and drifting snow. Have held off on a formal mention of VSBY reductions for now due to lower confidence and expected lower coverage if it were to develop.

Winds will be out of the WSW through the day today around 10-15 kt with gusts around 20kt. A strong arctic cold front will move through the area later tonight (~4-7Z) from west to east. Winds will become strong out of the WNW behind the front with gusts up to 30-35 kt likely. Winds ease slightly after daybreak but remain strong through the morning on Monday.

Petr

MARINE

Issued at 220 AM CST Sun Jan 18 2026

The gale watch has been upgraded to a gale warning for tonight into Monday morning for all of the IL and IN nearshore waters.

A heavy freezing spray warning has been issued for the nearshore waters east of Gary, IN.

A strong arctic cold front will move across the area tonight, bringing a period of gale force winds between 35 and 40 knots. These strong winds will slowly diminish on Monday with gales ending across the IL nearshore Monday morning and then across the IN nearshore Monday afternoon. Very cold temperatures will spread across the area behind this cold front and combined with the high waves, heavy freezing spray is expected across parts of the IN nearshore waters, mainly east of Gary, IN. cms

HYDROLOGY

Issued at 253 PM CST Fri Jan 16 2026

The upcoming extended period of very cold temperatures will likely result in the rapid development of ice on area rivers and streams which may increase the chance of localized ice jam flooding. Last week's heavy rainfall has resulted in increased streamflow in several basins, including the Fox, Des Plains, and Illinois River basins. This higher streamflow will result in a greater potential for freeze up ice jam flooding.

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES

IL...Cold Weather Advisory from 3 AM to 10 AM CST Monday for ILZ003- ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013- ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103- ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...None. LM...Gale Warning from midnight tonight to 9 AM CST Monday for Winthrop Harbor IL to Gary IN.

Gale Warning from midnight tonight to 3 PM CST Monday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

Heavy Freezing Spray Warning from midnight tonight to 3 PM CST Monday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.