textproduct: Chicago

KEY MESSAGES

- Windy and seasonably chilly conditions expected today with some scattered showers, wind gusts over 30 mph are expected this afternoon.

- East of Gary, lake enhanced showers this afternoon will transition to lake effect showers tonight with a slight chance of a thunderstorm near the shore late this afternoon/early this evening. Wind gusts to 45 mph possible near the northwest Indiana lakefront this afternoon/early evening.

- Coldest night of the season expected tonight with lows near/just below freezing across interior portions of northern IL.

DISCUSSION

Issued at 315 AM CDT Fri Oct 16 2026

Vigorous upper trough evident on water vapor imagery early this morning moving into the upper Mississippi Valley. The associated surface cold front has now pushed east of the CWA with gusty northwesterly winds ushering in a colder and less humid air mass. Showers associated with the cold front will move east of our CWA well before sunrise, however additional scattered showers are expected this afternoon in association with the mid-upper level trough moving across the area. Despite the drier low level air mass advecting in, a pocket of very cold air aloft associated with the trough (-27C at 500mb on 00z Bismark sounding) will aid in destabilization and support scattered showers this afternoon. While scattered showers are expected area wide late this morning into this afternoon, the arrival of the cold air aloft should result in a significant increase in lake induced instability resulting in more widespread and robust showers over Lake Michigan spreading into northwest Indiana (mainly east of Gary). Forecast soundings depict the top of the moist convective layer reaching above the -20C level this afternoon over southern Lake Michigan, which could even allow an isolated thunderstorm or two.

The cloud cover, scattered showers, and strong cold air advection should result in very little diurnal recovery in temperatures with temperatures holding nearly steady in the upper 40s to mid 50s. Strong and gusty northwest winds will only add to the chill with gusts over 30 mph likely today. Lake induced instability and less friction will result in even stronger winds over Lake Michigan bleeding onto the northwest Indiana shore this afternoon into early this evening when a few gusts to around 45 mph are expected.

Skies clear out early this evening and winds will gradually subside tonight, the exception being into northwest Indiana where lake effect showers will likely continue. The lake cloudiness and showers will keep temps relatively milder over northwest Indiana, but else look for the coldest night thus far this autumn. Have upgraded the freeze watch to a freeze warning and expanded it a bit farther south and east. Have buffered the freeze warning with a frost advisory for a couple of counties, though admittedly, tonight doesn't look particularly favorable for frost. Winds will be slow to subside, though over our western CWA very late tonight we could see winds get close to decoupling. The winds should prevent strong radiational cooling and with T/Td spreads expected to remain at or above 5F, frost potential is pretty iffy tonight. Nonetheless, with temps progged to get close to freezing and winds subsiding toward sunrise, felt it was prudent to hoist a frost advisory out of an abundance of caution and as a hedge in case temps were to get colder and dip to or just below freezing.

As the sharp upper trough shifts east of the region later tonight, inversion heights will come crashing down and should shut down the lake effect showers by or just shortly after sunrise Saturday. Outside of the decreasing lake effect cloudiness downwind of the lake Sat AM, look for sunny skies this weekend. Light winds with the still chilly air mass in place should result in below average temps in the 50s for highs Saturday. Saturday night the frost/freeze potential looks greatest away from the immediate lakeshore in northwest Indiana where strong radiational cooling is expected. Frost/freeze headlines will likely be needed Saturday night for at least portions of northwest Indiana and perhaps west into portions of northern IL as well.

Our impending cold snap looks to be short lived with warm air advection ramping up Sunday and highs rebounding back into the 60s. Unseasonably mild weather is expected next week with highs approaching 70 Monday and likely in the 70s the rest of the week. Average highs next week drop into the upper 50s, so we'll be looking at high temps 10 to nearly 20F above average by the middle and end of next week. After the shower threat ends over most of the area late this afternoon and downwind of the lake by early Saturday, no precipitation is expected through the rest of the weekend and next week looks dry as well.

- Izzi

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 626 AM CDT Fri Oct 16 2026

Key Aviation Messages for the current TAF period:

- Prevailing MVFR is expected through much of today.

- Strong northwest wind gusts 25 to 30 knots overnight, strengthening in excess of 30 knots this afternoon.

- Widely scattered showers are expected this afternoon, with lingering chances of lake effect showers around KGYY and northwest Indiana through tonight.

- Wind gusts diminish after 00Z with improving/clearing sky conditions.

Satellite imagery this morning is showing a few breaks in the cloud cover presently, with cloud bases lifting up to 2500 ft AGL. This brief window of VFR/higher MVFR is expected to be momentary as the next round of showers is moving southward through Wisconsin, which is expected to bring MVFR cigs back into northern Illinois later this morning. Northwest wind gusts remain around 20 knots this morning but are expected to increase to 25 to 30 knots through the morning. As deeper mixing occurs during the day, gusts in excess of 30 knots are expected. Isolated gusts between 35 to 40 knots are possible this afternoon, though the better chances remain just over 30 knots.

Widely scattered are expected late morning and through the afternoon over much of the area, with best chances in northwest Indiana as Lake Michigan. There is a slight chance for isolated thunderstorms in northwest Indiana and near KGYY, but the probability was too low for formal TAF mention presently. Showers are expected to slowly dissipate around sunset, with a band of lake effect showers expected KMGC. That band is forecast to drift westward toward KGYY around and after midnight for an additional chance for showers.

The pressure gradient will gradually weaken after 00Z, winds will turn more northerly and cloud cover will begin to clear. Wind gusts will diminish through the evening expected to end all together after midnight. VFR conditions are expected at the end of the TAF period.

DK

MARINE

Issued at 315 AM CDT Fri Oct 16 2026

West to northwest winds to 30kt this morning will veer more northerly and increase to gales to 40kt this afternoon. Northerly gales will continue this evening, with strongest gusts to 40kt+ likely within the lake enhanced convergence band and with more robust lake effect showers over the Indiana waters east of Gary. In addition to an isolated thunderstorm or two late this afternoon, conditions are expected to become favorable for waterspouts late this afternoon into this evening. Waterspout risk is expected to diminish late this evening as inversion heights lower. Lake effect shower intensity and coverage will decrease overnight also in response to the decreasing inversion heights.

LOT WATCHES/WARNINGS/ADVISORIES

IL...Freeze Warning from 5 AM to 8 AM CDT Saturday for ILZ003- ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-ILZ012.

Frost Advisory from 5 AM to 8 AM CDT Saturday for ILZ006- ILZ019-ILZ020.

IN...Wind Advisory from 1 PM this afternoon to 10 PM CDT this evening for INZ002.

LM...Small Craft Advisory until 1 PM CDT this afternoon for the IL and IN nearshore waters.

Gale Warning from 1 PM this afternoon to 1 AM CDT Saturday for the IL and IN nearshore waters.