textproduct: Chicago

KEY MESSAGES

- Record warmth is likely today, along with breezy/gusty southwesterly winds.

- Showers likely and some embedded thunderstorms Tuesday night into Wednesday morning, and again on Thursday.

- Turning much cooler into next weekend.

DISCUSSION

Issued at 206 AM CDT Mon Oct 12 2026

Fog has developed across parts of northern IN, mainly just east of the cwa border and other then some very shallow patchy fog and mainly across northwest IN early this morning, not expecting any widespread fog concerns.

An upper ridge will build across the region today bringing high temps in the mid 80s north to upper 80s south and made no changes to the previous forecast. Current cloud cover is expected to thin by midday and if mostly sunny skies materialize, its possible high temps may be a degree or two warmer then currently forecast. As the low levels mix and low level winds increase, southwest winds may gust into the 25-30 mph range this afternoon and these gusts may continue into this evening and periodically overnight as strong low level winds are expected tonight. And while temps are expected to quickly drop through the 70s early this evening, temps will level off in the upper 60s to near 70 for lows by Tuesday morning.

A weak trough of low pressure will move across the area Tuesday morning, shifting winds westerly but with little change to the airmass, high temps on Tuesday are likely to be nearly the same as today, ranging from lower 80s across northern IL, mid 80s for much of the Chicago metro and upper 80s for areas south of I-80. With dewpoints creeping into the mid 60s on Tuesday, heat index values south of I-80 may climb into the lower 90s Tuesday afternoon.

Precip chances for today and tonight, while already low, now appear too low for any mention and will have a dry forecast through Tuesday afternoon. If any isolated showers were to develop, the best time window appears to be around/just after daybreak Tuesday morning.

A cold front will move south into the area late Tuesday afternoon and slowly move south across the area Tuesday night. This will be the time period when showers and scattered thunderstorms are possible. Precipitable water values range between 1.5 and 2 inches Tuesday night into Wednesday morning with heavy rain possible, but there is still quite a bit of uncertainty for coverage and currently, areas south of I-80 are more favored for higher coverage. The SPC Day2 outlook also has a level 1 for severe thunderstorms into the far western part of the area. This potential may also be dependent on the location of the precipitation and if convection ends up further south.

Precipitation may end for most of the area Wednesday morning with the daylight hours on Wednesday mainly dry, especially north of I-80. Showers and scattered thunderstorms are then expected to develop and spread back across the area late Wednesday night into Thursday ahead of strong cold front that will move across the area Thursday night. Precipitable water values area also in the 1.5 to 2 inch range on Thursday with heavy rain again possible.

With strong cold air advection expected Thursday night into Friday, northwest winds may gust into the 35-40 mph range late Thursday night into Friday. There still remains uncertainty for how cold the airmass will be behind the front but considering how warm temps will be through midweek, it will be much colder with Saturday morning perhaps the coldest with lows in the lower/mid 30s. The ECMWF had been warmer and the GFS seems to be coming around to that solution as high pressure passes the area Sunday morning and then winds turn southerly with moderating/ warmer temps by Sunday. cms

AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 104 PM CDT Mon Oct 12 2026

Key Messages:

- Breezy southwesterly winds are expected this afternoon.

- A strenghening low-level jet may lead to a period of low- level wind shear tonight.

Breezy southwesterly winds are expected this afternoon with gusts generally in the 20-25 kt range. The gustiness should largely cease by this evening as the boundary layer decouples, which will open the door for a period of low-level wind shear tonight as a 45-50 kt low-level jet centered between 1500 and 5000 ft AGL strengthens over the region.

A cold frontal passage tomorrow morning will cause winds to adopt a westerly to west-northwesterly direction. Sustained wind magnitudes are generally favored to remain near 10 kts, though occasional gusts to around 20 kts may be observed -- mainly in the morning. Winds will then slacken towards the end of the 30-hour TAF period at ORD and MDW. This may allow for a lake breeze to push inland and result in an easterly wind shift at ORD and/or MDW, though the best potential for this appears that it may not come until around or just after 00Z.

Could not rule out a brief sprinkle or light shower this evening as isentropic ascent ramps up commensurately with the strengthening low-level jet. However, at this time, the better chances for any raindrops to be observed at ground level appear to be east of the terminals, so have kept the TAFs dry. Otherwise, VFR conditions will prevail through the TAF period.

Ogorek

CLIMATE

Issued at 235 PM CDT Sun Oct 11 2026

Here are the record warm temperatures most likely to be threatened or broken early this week.

Monday October 12th Record High Temps: Chicago's current record high: 84F in 2008 Rockford's current record high: 85F in 2008

Tuesday October 13th Record High Min Temps: Chicago's current record high min: 67F in 1920 Rockford's current record high min: 61F in 2008

NWS Chicago

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...Small Craft Advisory until 4 AM CDT Tuesday for the IL nearshore waters.