textproduct: Chicago

KEY MESSAGES

- A wind advisory is in effect due to the expected powerful winds, gusting over 50 mph at times, tonight into Monday morning areawide. Gusts may reach 55 to 60 mph at times in northern Porter County, Indiana as stronger winds move off of Lake Michigan.

- Wind whipped snow showers and flurries are expected late tonight through Monday morning, especially north of I-88/I-290 where locally an inch or two of accumulation could result in hazardous travel. A Winter Weather Advisory has been issued for far northern Illinois (Ogle, Winnebago, Boone, northern DeKalb, McHenry, northern Kane, northern Cook, and Lake Counties).

- Temperatures will continue to plummet through tonight. Expect wind chills close to zero Monday morning.

UPDATE

Issued at 936 PM CST Sun Dec 28 2025

In coordination with WFO MKX, opted to issue a Winter Weather Advisory for far northern Illinois, mainly north of I-88. In these areas, localized accumulations of 1-2", the very strong westerly winds, and patchy ice from lingering moisture freezing should contribute to hazardous travel being more prevalent in the advisory counties. With snow expected to be falling into and/or through the morning commute as the strong winds continue, the added concern for impacts to the morning commute warranted the addition of a Winter Weather Advisory.

Expect lighter snow showers and flurries for most of the area through the late evening, followed by more widespread falling snow into Monday morning. Updated forecast has locally 1-2" of snow in the advisory counties, which may be enough to cause an additional hazard from areas of blowing and drifting snow, particularly on north to south roads in open/exposed areas.

For northwest Indiana, there had been concern for considering an upgrade to High Wind Warning for areas near the lake in Porter County. Still can't rule out gusts to 60 mph near the lake, but confidence in occurrence and frequency wasn't high enough based on latest forecast guidance to upgrade to a warning. On the other hand, northeast Porter County may need to be included in a Winter Weather Advisory as wind blown lake effect snow develops after the overnight through Monday morning system snow.

Castro

DISCUSSION

Issued at 240 PM CST Sun Dec 28 2025

Through Monday:

Heavy rain and thunderstorms are on a break here locally during the early afternoon after an eventful morning. Widespread light to moderate rain impacted most of our CWA and we saw a corridor of mostly sub-severe thunderstorms near and south of I-80. One lone severe storm managed to produce some noteworthy wind damage in Livingston County. We also received a handful of reports of street flooding. It appears that over half an inch of rain fell around a big majority of our CWA this morning with a sizable corridor of 1-2" near and south of I-80. Here in Romeoville, we've received over 1.1" since this morning.

Lighter, densely scattered showers now continue near and north of I- 80 as of around 2 PM as the warm front continues to push north ahead of the approaching cyclone. The MUCAPE reservoir has not kept up with the front on its northward progression, which explains the absence of thunder now.

Down into central IL, we've seen convective activity quickly develop along the storm's strengthening cold front. Embedded severe convection is crossing the Illinois River near Peoria as of 2 PM. Latest SPC mesoanalysis shows between 500 and 1000 J/kg of surface- based instability is available across central IL and stretching into our far southern CWA along and ahead of the line. This comes as temperatures have warmed to near 70 degrees and dewpoints into the lower 60s in central IL within the storm's warm sector. It also depicts 30 kt of 0-1 km shear along this line and 50 to 60 kt of 0-3 km shear. This line will race toward the east at 50 to 60 mph through the remainder of the afternoon. Expectations are for thunderstorm coverage to fill in along the front into mid-afternoon as the accelerating warm conveyor continues to transport moisture and instability northward. The better part of the Chicago metro could be in for additional elevated storms near and south of the storm's triple point. But the more appreciable ingredients for severe convection still look to favor areas roughly along and east of I-55 and south of I-80 during the latter half of the afternoon.

Primary severe hazards will be damaging wind gusts to 60 to 70 mph and a few tornadoes. The threat for both has increased now that surface-based storms are basically certain. A Tornado Watch was recently issued from SPC in this corridor. Very heavy rainfall is also possible along this line, but given the progressive nature of the front, not really anticipating many flooding issues outside of areas that saw problems earlier today; those could be resurrected by the added rainfall. The window for severe convection in our area looks rather brief, roughly 3 to 6 PM. Over any given area, the severe threat will only last a handful of minutes. The line will push east of the CWA by 6 PM.

Winds will ramp up very quickly in the wake of this system/cold front late this afternoon and evening. Most of the CWA should be looking at gusts out of the west at 30 to 35 mph by dusk building to 45 to 50 area-wide by the end of this evening. Such winds are expected through the night and into early Monday, with steady but very gradual easing expected during the morning and afternoon. No changes were made to the going Wind Advisory. An upgrade to a High Wind Warning was considered in Porter County, IN where there are concerns for a period 60+ mph winds to protrude inland off the lake. While this looks to be confined to only a handful of miles inland from the shore, these sorts of winds would be moving over I-94 and other major arterials along the lakeshore possibly during portions of the morning commute. Confidence wasn't quite there to warrant upgrading yet, but considerations will still be made.

Also in the wake of the front, temperatures will drop like a rock this evening and tonight, as many as 20+ degrees in just a few hours. It's tough to say the extent of impacts we'll see from any flash freezing, but at least some slick spots on roads appear likely to form. Any lingering puddles or ponding will freeze, but hopefully these will mostly be found 26off of roadways. The strong winds this evening should help dry roads off before freezing over. However, even if no snow on the roads, be aware that areas could be slippery late tonight into tomorrow. Also prepare for a much colder day with morning winds chills near and below zero, and in the single digits above zero during the afternoon.

Snow showers are expected to wrap around the low to the north and fall on the CWA this evening into Monday. The best chances to see true snow showers through most of tonight will be north of I-80 where flurries will be favored farther south. The better push of snow showers appears to come late during the overnight and into Monday morning as a secondary boundary pushes across. Forecast soundings depict a few hour window where added forcing from this wave will interact with a rather deep DGZ presence and could churn up some moderate snow at times, especially in our northern CWA and around Lake Michigan. The windy conditions will only make matters worse on the roads leading to blowing snow and poor visibility. Even lighter snowfall will bring about hazardous travel conditions. Be prepared for sudden changes in visibility in snow tonight and Monday morning, including during the commute. Snow may linger into the afternoon, mainly around the lake and into northwestern IN with flurries possible elsewhere, but most of the area will see an end to the impactful snow showers sometime during the morning. Guidance favors around an inch of accumulation up near the WI state line and a couple to several tenths elsewhere around the area.

Doom

Monday Night through Sunday:

The upper level low that is driving this weekend's weather will be over Quebec by Monday night. Another upper level low is expected to drop southward from Hudson Bay Monday night through Tuesday. While these two upper level lows phase with each other, impacting the weather out east, it will send a series weak disturbances extending back over Lake Michigan that could provide a couple additional rounds of wintry precipitation. Unfortunately, models are showing little agreement providing lower confidence in the details.

The first weak disturbance drops southward out of Canada on Tuesday. The Euro ensemble has a surface low in south-central Canada dropping into northern Minnesota before weakening as it moves from the Minnesota arrowhead to Michigan's western mitten. The GEFS meanwhile has a weaker wave and a more eastern track. For now, kept snow out of the forecast. Maybe some flurries or light snow is possible for areas closer to Lake Michigan, but unless models shift more westward, dry conditions should prevail.

Models have shown some decent agreement that as the previously mentioned upper lows phase around each other Tuesday night into Wednesday, they will slowly retrograde westward into Ontario with a strengthening 300 mb 100+ knot jet and a reflected deepening surface cyclone. With a weak mid level wave dropping southward, a surface cold front is expected to pass over the area on Wednesday with much more robust cold air advection behind the front. No changes were made to the PoPs as latest NBM run keeps chances for snow for much the area. There is still plenty of model disagreement on exact timing and snow amounts. And while current indicators are that it does not have a signature of a major snow storm, it could provide a coating on the ground. Holiday revelers may expect some snow falling down as 2025 runs out of time.

Temperatures will feel much more winter like through the week. As northwest winds persist through Monday night into Tuesday morning, single digits to low teens are expected in the morning with wind chills at or just under zero degrees F. High temperatures are expected in the 20s to just below freezing Tuesday and Wednesday. New Years Day looks to be a chilly one as temps drop once again behind the front. The NBM is suggesting solidly in the 20s for highs, but that might be biased by the GFS/GEFS having no snow, whereas the Euro suite is advertising highs in the teens (a likely result "if" there is a coating of snow on the ground).

Temperatures are expected to climb slowly back into the upper 20s and low 30s for the end of the week/weekend. There is a chance for another winter system that could bring some more precip to the area, potentially on Sunday, but models are not showing a lot of agreement at this distance to have great confidence.

DK

AVIATION /06Z TAFS THROUGH 12Z TUESDAY/

Issued at 1126 PM CST Sun Dec 28 2025

Aviation forecast concerns:

- Period of snow overnight into Monday morning, with IFR visibilities and some accumulations (1-2 inches mainly NW of Chicago) likely.

- Strong west-northwest winds with gusts around 40 kts overnight into Monday, gradually diminishing during the afternoon.

Deep surface low pressure was pulling away from the area across Lake Huron late this evening. In the wake of the low, strong low level cold advection and a tight surface pressure gradient was producing west-northwest winds gusting 35-40 kts across the region. These winds will persist into Monday morning before gradually decreasing during the afternoon.

An area of wrap-around snow and snow showers over much of MN/northeast IA/WI and northern IL will pivot across the terminals tonight into Monday morning. IFR visibilities and some accumulation (1-2 inches especially northwest of Chicago) are likely during the predawn and early morning hours of Monday. Organized snow should end by 14-15Z across the Chicago terminals (around 13Z RFD), though light non-accumulating flurries may persist at times from a lingering MVFR cloud deck through the afternoon. MVFR CIGs will likely scatter out Monday evening, with winds continuing to diminish.

Ratzer

MARINE

Issued at 240 PM CST Sun Dec 28 2025

- Gale Warning in effect from 5 PM Sunday to 6 PM Monday from Winthrop Harbor IL to Gary IN.

- Storm Warning in effect from Gary IN to Michigan City IN, from 6 PM Sunday to 3 PM Monday.

A powerful cold front will sweep across the lake late Sunday, resulting in a rapid increase to gale force and storm force west-southwest winds. As low pressure continues to rapidly deepen near Lake Huron Sunday night into early Monday, westerly winds will further increase. Confidence in occurrence and duration of storm force speeds/gusts is highest for the southeast portion of the lake.

Freezing spray will also be possible late tonight and continue into Monday as air temperatures are expected to be in the lower 20s and possibly into the teens.

Doom

LOT WATCHES/WARNINGS/ADVISORIES

IL...Wind Advisory until 3 PM 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.

Winter Weather Advisory until 3 PM CST Monday for ILZ003- ILZ004-ILZ005-ILZ006-ILZ008-ILZ011-ILZ012-ILZ103.

IN...Wind Advisory until 3 PM CST /4 PM EST/ Monday for INZ001- INZ002-INZ010-INZ011-INZ019.

LM...Gale Warning until 6 PM CST Monday for the IL nearshore waters.

Storm Warning until 3 PM CST Monday for the IN nearshore waters.