Weather in Chicago in September

Prime time. September is about as good as Chicago gets. Highs average 21.9 °C, lows 16.5 °C, and rain falls on 10 days — nothing in the month is working against you.

September is the highest-scoring month of the twelve. The nearest rival is July, and the month at the other end of the year is February.

Rain on 10 days, 2 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average September reaches 30 °C; the day barely swings — 5.5 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 30.7 °C and the coldest night fell to 8 °C, and the wettest single day dropped 79 mm — roughly 92% of the month's rain in one day.

September is moderately variable: 15 mm in the driest year against 283 mm in the wettest, around an average of 86 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind is light at 14.5 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 76%, high enough to notice on the warm days without dominating them.

How September sits in the year

The month is on the way down: 3.2 °C cooler than August, with October dropping another 6.7 °C. The first week and the last are not the same trip.

Daylight in September

12.5 hours of daylight, losing 1.4 hours across the month. That is between Chicago's extremes of 15.2 and 9.2 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 30.2 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in Chicago versus nearby

If Chicago is one option among several, the nearby comparison is worth making. Milwaukee is close enough to be a coin toss — within a degree on temperature, the same number of rain days. Grand Rapids is close enough to be a coin toss — within a degree on temperature, the same number of rain days.

So: September is the answer for Chicago. If it is booked out or priced out, July is the next best thing at 4 points behind, and February is the month to keep off the shortlist.

Every month in Chicago

See all twelve months in Chicago, or where else to go in September.