textproduct: Chicago

KEY MESSAGES

- Temperature moderation will be underway Monday with above normal temps expected through Saturday.

- Low (less than 20%) chance for light rain/sprinkles across far NE IL Monday afternoon.

- Light rain/drizzle/patchy fog expected Christmas Eve PM into Christmas AM.

DISCUSSION

Issued at 125 PM CST Sun Dec 21 2025

Through Monday Night:

Strong high pressure is cresting the area this afternoon and will continue to shift east into this evening. A series of waves resulting in pushes of warm advection will then move across the area through Monday night. The first will pass late tonight bringing an increase in mid/high level cloud cover which will combine with modestly increasing southerly winds behind the departing high to bring rising temperatures overnight. A somewhat better organized wave will cross the area Monday afternoon, keeping abundant cloud cover in place and bring a low chance (less than 20%) chance for light rain or even just sprinkles to areas from roughly Rockford southeast across the northern Chicago metro area. Warm advection aloft will again increase Monday evening with steady southwest low level winds supporting a milder night with lows in the mid to upper 30s for most areas.

MDB

Tuesday through Sunday:

A weak cold front/wind shift will be dissipating across the area Tuesday with dry weather expected. Cloud cover is tricky for Tuesday, with the potential for low clouds taking their time to scatter out in the morning and then possible mid/high level clouds. But Tuesday has the potential to become mostly sunny in the afternoon, which would help high temps reach well into the 40s and possibly lower 50s across the south. Light winds and at least mostly clear skies will allow lows Tuesday night to dip into the upper 20s/lower 30s.

Clouds will be on the increase Wednesday as the next weak system moves across the area Wednesday night. As has been advertised over the past few days, there is quite a bit of uncertainty for how far north the warm front will lift across the local area and thus how warm temps will rise on Wednesday, especially with the increasing cloud cover and the chance of light rain/drizzle by mid/late afternoon as the wave approaches. Maintained the previous forecast's temps with highs Wednesday ranging from the lower 40s north to the lower 50s south. The best chance/highest coverage for light rain or drizzle appears to be Wednesday evening and maintained previous likely pops during this time period. Temps will likely hold steady from Wednesday's high temps across the north and likely rise a few degrees into at least the mid 50s across the south by Thursday morning. With the boundary likely still nearby or across the area, maintained a chance of drizzle into Christmas day but also added patchy fog for Wednesday night into Christmas morning. While it might be a bit early to say where the fog will form, as trends look now, there will probably be fog, possibly dense near the boundary.

Also maintained previous forecast temps for Thursday with highs ranging from the upper 40s north to around 60 south. However, there appears to be growing consensus from the models that the warm front will lift across the area Thursday night as new low pressure passes north of the area Thursday night into Friday. This could lead to rising temps Thursday evening through Friday morning making for a difficult daytime high temp and nighttime low temp. Another trailing weak cold front is then expected to move across the area Friday. Models suggest a stronger cold front arriving next weekend with perhaps well above normal temps on Saturday and near/below normal and falling temps Sunday. cms

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/

Issued at 526 PM CST Sun Dec 21 2025

Key Aviation Messages for the current TAF period:

- Gusty southerly winds are expected Monday

- A marginal risk for low level wind shear (LLWS) Monday morning

- Chance for MVFR cigs Monday evening.

VFR conditions are expected overnight. Light winds will remain out of the southwest as high level clouds slowly move over the air space.

A 40 to 50 knot low level jet will increase Monday morning. Recent models depict the core of the jet above 3000 feet, so there is lower confidence in the strength and duration of stronger winds aloft to merit the addition of LLWS at this time. Additionally, there is also uncertainty on how strong the inversion will be tomorrow morning, which would inhibit the amount of mixing for stronger surface wind gusts. That being said, the inversion should erode enough to allow for southerly wind gusts of 20 to 25 knots through the late morning and early afternoon.

A weak boundary will pass over the area in the late afternoon. Mid level saturation will increase cloud cover, but low level dry air lowers confidence in precipitation. While there is a less than 20 percent chance for a stray shower/sprinkle in the afternoon, the TAFs were kept dry. There is a better chance for MVFR cigs behind the boundary Monday evening.

DK

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.