textproduct: Chicago

KEY MESSAGES

- Strong westerly winds (gusts of 50 to 60 mph) and much colder temperatures expected today. A period of flurries and showers will also occur today, especially north of Interstate 80.

- Blustery and cold weather continues through the evening hours on Thanksgiving Day.

- Impactful snow appears increasingly likely for the region this weekend. It's too early for highly specific snowfall amounts and locations, but there is a distinct potential for 6"+ amounts (and higher end travel impacts) in portions of the area.

- Well below normal temperatures will persist into or through next week, perhaps with additional chances for snow.

DISCUSSION

Issued at 329 AM CST Wed Nov 26 2025

Through Thursday:

Winds have come up quicker than originally thought in the wake of the strong cold frontal passage early this morning. This prompted us to move up the start time of the wind advisory just shortly after midnight. Aside form this, no other changes have been made to the going headlines.

A robust storm system continues to take shape across the Upper Midwest into the Upper Great Lakes this morning. Early morning water vapor imagery illustrates this nicely, with a negatively tilted trough axis currently surging northeastward into WI along the southeastern periphery of the strengthening mid-level circulation center located just southeast of MSP. Strong dynamics associated with this trough will continue to deepen the surface low to a stout sub 995 mb central pressure as it becomes occluded this morning over northeastern WI and far northern Lake Michigan.

While a significant winter storm will ensue across the Upper Midwest into the Upper Great Lakes in association with this system, our main weather story today will be the persistent strong gusty westerly winds and much colder temperatures. As noted above, we have already seen a quicker uptick in the winds early this morning, with some occasional gusts already exceeding 45 to 50 mph. Unfortunately, this is just the beginning, as 50 to 55 mph gusts look to become rather common across the area this morning and persisting this afternoon. There have been a good amount of upstream observations of 55 mph wind gusts across IA overnight, and really see no reason why such wind magnitudes will not materialize throughout all of northern IL into northwestern IN today.

We have opted to hold with the wind advisory for today, but with speeds of 50-55 mph (possibly even briefly as high as 60 mph) this will be a higher end wind advisory event. Accordingly, if the winds overperform even slightly from our current forecast, portions of northern IL could need to be upgraded to a High Wind Warning through the daylight hours today. Winds this strong can still result in minor property damage and lead to power outages.

Wind gusts will begin to ease a bit this evening into tonight, so the current 9 pm end time of the wind advisory still looks good. However, expect blustery conditions to persist tonight through Thanksgiving Day as west-northwesterly winds continue to gust to 30 to 35 mph. The combination of the gusty winds and the much colder temperatures will result in wind chills remaining in the teens to low 20s.

Aside from the winds, wrap around moisture along the backside of the Upper Great Lakes low will allow for a period of snow showers and flurries today, most notably to the north of I-80 and into far northwestern IN. Some minor accumulations may materialize in these areas from this activity, but amounts will remain under a half inch and likely relegated to grassy, colder, or elevated surfaces.

KJB

Thursday Night through Tuesday:

The main forecast focus is on the widespread accumulating snow event this weekend, centered on Saturday from the early morning hours through the evening. Despite the snow onset being about 3-days away, there continues to be good ensemble agreement in an impactful, plowable snowfall for a sizable chunk of our area, particularly with northward extent. The time left until the event adds inherent uncertainty common in winter weather forecasting. Looking at the various ensemble systems, the largest spread is in the track and strength of the synoptic system, which will modulate top end amounts and also any potential for rain (or drizzle) to mix in with the snow across portions of the area.

Quiet conditions are expected prior to our increasingly likely impactful snow event. After a blustery start to Thanksgiving evening, from later Thursday night into Friday, ~1030 mb surface high pressure transiting the region will result in lighter west-northwest winds, though temps will be well below normal for the date (teens to mid 20s lows and highs around 30F into the lower 30s).

Returning to the weekend main event, big picture wise, a strong short-wave trough will come ashore on the Pacific NW coast on Thursday-Thursday night. Then in response to amplifying ridging into the Gulf of Alaska, this short-wave will dig into the central and southern Rockies and result in lee surface cyclogenesis over eastern or southeast Colorado. The surface low will broaden and become elongated on Saturday from the lower MO Valley to the lower and mid MS Valley. The details then diverge a bit Saturday evening into Sunday, serving to at least modulate the event magnitude (QPF, snow, impacts).

A broad area of strong warm and moist advection will develop over the central US, with this and upper jet diffluence resulting in an expansive area of precipitation well ahead of the surface low path. At this time, there remains overall good agreement in the thermal profile and surface wet bulb temps being cold enough for snow from snow onset through early Saturday evening, and much of this precipitation being from the warm advection regime. Later Saturday evening and night is the main timeframe with larger spread in the spectrum of outcomes.

To simplify things a bit, we're seeing roughly two "camps" in solutions, between the notably stronger physics based ECMWF and EPS ensemble, vs. the overall weaker member solutions of the ECMWF AIFS and EPS-AIFS, GEFS, Canadian (GEPS), and UKMET (MOGREPS-G) There is better clustering in a surface low track somewhere near the CWA or just south, but a much larger % of deeper surface low members in the EPS. The deeper surface low evolution would entail a longer duration of deformation type (cold conveyor belt) precip into early to mid Sunday morning (more QPF, and more snowfall for areas that stay all snow), but also conceptually a higher chance for warmer air at the surface to possibly result in p-type issues extending farther north.

On the other hand, the weaker solutions would have predominantly warm advection snow and deformation focused farther northwest, cutting down into the QPF and snow amounts somewhat. Interestingly, the 850 mb temps are pretty uniformly forecast to remain below 0 Celsius (only a 10-20% chance of 850 mb temps >=0C reaching the US-24 corridor on the 00z EPS). So another item we'd likely have to contend with is the trajectory and expanse of the mid- level dry intrusion (would likely be larger in a stronger system), which could result in drizzle mixing in with the snow or a changeover to drizzle. For now, with wet-bulb temps forecast to remain mostly cold enough for snow, but conceptual support for some rain mixed in on Saturday night for parts of the area, indicated a chance of rain over roughly the southeast half or so of the area. As the surface low tracks into the central Great Lakes on Sunday, strong cold advection will transition any non- snow precip back over to light snow, along with gusty northwest winds. A final note worth mentioning is that periods of onshore flow with this system may result in milder air from over the lake cutting down on ratios and amounts some.

The spectrum of outcomes still ranges from a light to moderate event on some of the guidance members to a bonafide snowstorm on a surprisingly large % of members, particularly in the ECMWF/EPS suite, which remains the most robust. Can't ignore this despite it being three-days out, because the above normal column moisture (PWATs likely over 0.6" into central IL) and steep lapse rates above 500 mb do lend credence to periods of heavier snowfall rates. The major ensemble systems are basically in unanimous agreement in 1"+ snowfall in 24-hours (10:1 ratio) already, with even 50-80% probs for 4"+ amounts, especially near/north of I-80. The top end potential (6"+) has less overall guidance membership amongst all the ensemble systems, but with that said, the EPS has a strikingly large % of members with 6"+ snow amounts (60-90% near/north of I-80). Ratios where p-type remains snow should likely be at least 10:1 to perhaps as high as 12-15:1, just to give a reference on these outputs.

In the wake of the system, the decided trend is towards a couple day quiet but cold period in its wake. Any nights that fully clear out under surface high pressure will likely be quite cold (single digits or even below zero in spots) if a good snowpack is established, which remains to be seen, but is becoming the more likely outcome. Finally, we'll have to keep an eye on any lower amplitude short-waves for swaths of light snow accumulations next week amidst an overall well below normal temperature regime. The first of these timeframes to watch is later Monday through Monday night.

Castro

AVIATION /12Z TAFS THROUGH 18Z THURSDAY/

Issued at 507 AM CST Wed Nov 26 2025

Key Messages:

- Strong gusty westerly winds through the period, strongest during the daylight hours of today.

- Scattered flurries and snow showers, with brief MVFR VSBY restrictions possible.

The primary weather concern continues to be the strong westerly winds. A strong area of low pressure over the Upper Great Lakes will result in very strong and gusty westerly winds, particularly during the daylight hours of today. Frequent gusts of 40-45 kt are expected, and there is some potential for a few sporadic gusts up around 50 kt. While the magnitude of the gustiness will ease into this evening, blustery west- northwesterly conditions will persist through Thanksgiving.

MVFR CIGS will also persist today, and there will also be some occasional flurries and/or snow showers through the day. Some of the more vigorous showers could result in brief MVFR VSBY restrictions, but little in the way of accumulation is anticipated.

KJB

MARINE

Issued at 329 AM CST Wed Nov 26 2025

Key Marine Messages include:

- Gale Warning transitioned to a Storm Warning for today for for the Illinois and Indiana nearshore waters of Lake Michigan. The Gale warning then continues tonight through Thursday evening. - Peak wind gusts of 50 kt Storms today, tapering to 35 to 40 kt tonight and on Thursday.

Westerly winds will continue to increase this morning, with speeds likely to top out around 50 KT during the daylight hours today. While the magnitude of winds will gradually ease tonight onward, they will remain at or above gale force (35 to 40 kt) through Thursday evening.

A Storm Warning has been issued for both the Illinois and Indiana near shore waters for today. This will transition back to a Gale Warning tonight through Thursday evening.

Borchardt/KJB

LOT WATCHES/WARNINGS/ADVISORIES

IL...Wind Advisory until 9 PM CST this evening for ILZ003-ILZ004- ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019- ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104- ILZ105-ILZ106-ILZ107-ILZ108.

IN...Wind Advisory until 9 PM CST /10 PM EST/ this evening for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Gale Warning until 6 AM CST early this morning for the IL and IN nearshore waters.

Gale Warning from 9 PM this evening to 10 PM CST Thursday for the IL and IN nearshore waters.

Storm Warning until 9 PM CST this evening for the IL and IN nearshore waters.