textproduct: Chicago

KEY MESSAGES

- Gusty winds will abate this evening.

- There is about a 20% chance for some areas to pick up a dusting of snow Saturday morning.

- Waves of thunderstorms may occur on Sunday. There is a Level 2 out of 5 threat for severe thunderstorms Sunday afternoon 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.

- A period of cold temperatures is expected Monday and Tuesday, with overnight wind chills ranging from 0 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 249 PM CDT Fri Mar 13 2026

Through Saturday:

A strong pressure gradient, associated with deep low pressure moving across northern Lower Michigan, continues to support damaging westerly wind gusts of 50 mph to occasionally as high as 60 mph across northern IL into northwestern IN. Overall, expect these speeds to gradually ease through the mid and late afternoon hours as the area of low pressure continues eastward. The current High Wind Warning is set to end at 4 PM this afternoon. However, we may soon be able to convert this warning to a Wind Advisory for the remainder of the afternoon, but I would like to see peak hourly wind gusts drop below 55 mph before doing so. Either way, expect wind gusts to gradually ease into early this evening, before becoming light and variable tonight as a surface high shifts overhead.

Tonight into Saturday, a sharp west-northwest to east-southeast oriented baroclinic zone will become draped right across our region in the wake of today's Great Lakes storm system. This will set the stage for bands of strengthening low-to mid-level frontogenesis across our area on Saturday in response to an increasing southerly mass wind response to the next major storm system taking shape across the Plains. Consequently, this may induce some developing bands of snow that slide northward across our area through the day Saturday. However, much of this activity may end up as virga due to lingering low-level dry air. Nevertheless, there is about a 20% chance for some light snow Saturday, though with temperatures warming into the low 40s in the afternoon, we don't expect any real travel impacts.

KJB

Saturday Night through Friday:

A deepening trough is expected to be digging into the central Plains Saturday night with a surface low developing leeward of the Rockies. As the low develops, strong warm advection will begin to materialize ahead of the low across MO, IL, and IN which will push the baroclinic zone over IL and IN northward as a warm front. Last forecast trends continue to show the warm front lifting well into southern WI by Sunday morning which should keep the band of precipitation forecast to develop along it north of our area. However, a few rain and/or snow showers (20-30% chance) may be seen Saturday night near the IL-WI line. Otherwise, Saturday night should largely be precipitation free with just gradually warm temperatures through the night and breezy southeast winds gusting around 20 mph.

Heading into Sunday, the surface low will begin to lift into the Mississippi Valley and western Great Lakes continuing to deepen as it does so. The combination of diffluent flow aloft, the approaching surface low, and warm advection will generate a lot of synoptic ascent across northern IL and northwest IN on Sunday which should be more than sufficient to generate scattered showers and thunderstorms, especially along and south of I-80 where the greatest moisture and instability is forecast to be present. Latest forecast soundings with the 12z guidance suite have actually come in with more mid-level capping due to the warming temperatures aloft which looks to keep the instability more of a limiting factor. However, given the aforementioned forcing suspect that some of this capping will be overcome and allow a broken line of showers and thunderstorms to develop ahead of the cold front Sunday afternoon. Couple these ingredients with the 40-50 kts of shear in place and conditions continue to look favorable for a few strong to severe thunderstorms to develop as well. With the more limited instability it appears the main threat with any severe storms will be damaging winds in excess of 60 mph, but with the veering low-level wind profiles a few tornadoes cannot be ruled out. For these reasons a marginal risk (level 1 of 5 severe threat) remains for most of northern IL with a slight risk (level 2 of 5 severe threat) for areas east of I-55.

The surface low will move overhead Sunday evening and drag a cold front into and eventually through the area Sunday night which will bring the severe threat to a close by 8-9 PM Sunday evening. behind the front, temperatures are forecast to quickly cool overnight which will transition the rain over to snow from west to east Sunday night. While there remains a chance (10-15%) for a period of freezing rain and sleet to develop as temperatures cool, there continues to be some uncertainty as to how quickly temperatures will cool aloft and thus have just opted to maintain a rain/snow mix mention in the forecast during this period. Once snow begins it is expected to prevail through the day on Monday as the system's deformation band slides through the area. With temperatures on Monday forecast to be in the 20s snow accumulations are expected to occur, but there continues to be some uncertainty in snow rates and amounts. The latest thinking is that snow accumulations would generally be in the 2-4 inch range (60-80% chance) for this event with the highest amounts forecast to occur north of I-80 and in northwest IL. However, there remains a 15-20% chance for localized amounts upwards of 6 inches to occur.

Regardless of the snow amounts, the main concern with wintry side of this system will be the threat for blowing and drifting snow as gusty northwest winds develop behind the low. With wind gusts expected to be in excess of 40-45+ mph Sunday night into Monday any falling snow will be blown around and if snow can be "fluffed" up enough as temperatures cool then some drifting snow may also materialize leading to hazardous travel. Given that there is still uncertainty in snow amounts, rates, and character we have opted to hold off on issuing a Winter Storm Watch with this forecast package. Though if trends continue then a consideration for a winter weather headline will be needed with future forecasts.

While snow will gradually taper Monday evening as the low and associated trough shift east of the region, the upper pattern will remain in a northwest flow regime. This regime will keep much colder temperatures in play through Tuesday with overnight lows in the single digits and teens with wind chills forecast to dip below zero especially Monday night. Additionally, this pattern will also put northern IL and northwest IN in a favorable spot for clipper systems to brush the area and bring us more chances for precipitation. The first of these clippers is forecast to move through Tuesday night into Wednesday which currently looks to fall mainly as snow, but there is some uncertainty as to the coverage and intensity of any precipitation locally. Otherwise, the upcoming week looks somewhat tranquil with just moderating temperatures through the week until our next chance at some precipitation arrives late week into next weekend.

Yack

AVIATION /00Z TAFS THROUGH 06Z SUNDAY/

Issued at 638 PM CDT Fri Mar 13 2026

WNW winds gusting around 30 knots at TAF issuance will veer NW while diminishing this evening, with gusts under 15 knots by midnight. Winds at around 5 knots will then slowly veer from NW to ESE overnight through late Saturday morning. The shift from NNW to NNE should occur around 12Z. Winds will remain ESE through the evening, with gusts over 20 knots developing by around sunset.

Coverage of low-end VFR clouds may slowly increase tonight while gradually lowering into high-end MVFR levels. Have maintained FEW/SCT coverage tonight and Saturday, but a brief period of shallow BKN MVFR ceilings cannot be ruled out late morning into the afternoon. Additionally, SN from a mid-level cloud deck (bases around 10kft) midday may survive a layer of dry air and seed the shallow MVFR clouds with VFR -SHSN. Chances under 30 percent are too low to include in the TAF at this time.

Kluber

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Gale Warning until 10 PM CDT this evening for the IL and IN nearshore waters.