Weather in Chicago

August is the warmest month (average 22.6°C, high 25.1°C) and January is the coolest (average -2.6°C, low -5.0°C). That 25.2°C swing in monthly averages is the first thing to plan around in Chicago.

Rain is wet season runs from April to August, inside an annual total of 982 mm. The wettest month is May at 117 mm; the driest is January at 48 mm. Chicago is in United States at 41.9°N. The 2001–2020 NASA POWER daily record describes a continental climate with a wide temperature swing. On this site the months that score closest to a 22°C day, lighter rain, and moderate humidity are July, August, and September.

Best months to visit Chicago

The three months with the highest comfort score are July, August, and September: July (22.5°C average, 95 mm, 78% humidity); August (22.6°C average, 105 mm, 77% humidity); September (19.2°C average, 86 mm, 76% humidity). They fall in calendar order. The score rewards averages near 22°C, lower rainfall, and humidity near 60%. It is a climate score, not a festival or price calendar.

If you want the wet season itself — fewer crowds, greener landscape, heavier rain — aim at April–August instead of the score.

Hot and cool months in Chicago

Chicago has a 25.2°C gap between its coolest monthly average (-2.6°C in January) and its warmest (22.6°C in August). That is a northern-hemisphere pattern.

Mean high across all twelve months is 12.5°C and mean low is 7.0°C. These are 20-year grid averages, so a city station can read a few degrees warmer or cooler.

Rainfall pattern

The wet season in Chicago starts in April and ends in August (April, May, June, July, and August). May is the core of it at 117 mm. January is the other extreme, with 48 mm.

A rainy day here is a day with at least 1 mm in the NASA POWER series. May averages 13 such days; January averages 8.

The calendar in Chicago

January is the coolest month, with lows around -5.0°C and highs near -0.2°C. Rainfall is 48 mm. February brings 54 mm and 8 rainy days; temperatures run from -5.1°C to 0.3°C. March stands apart from the months beside it: 4.9°C / -0.7°C and 62 mm. The wet season opens in April. Expect 95 mm and 12 rainy days, with nights around 3.8°C. May is the wettest month — 117 mm and 13 rainy days, with 83% humidity. June brings 102 mm and 13 rainy days; temperatures run from 15.1°C to 21.1°C.

July stands apart from the months beside it: 25.1°C / 19.8°C and 95 mm. By August the wet season is ending. Chicago still sees about 105 mm, but the next month is usually leaner. In September, Chicago averages 21.9°C by day and 16.4°C at night, with 86 mm of rain. In October, Chicago averages 15.2°C by day and 9.6°C at night, with 99 mm of rain. November: 8.6°C high, 3.5°C low, 61 mm rain, 80% humidity. December stands apart from the months beside it: 2.6°C / -1.7°C and 58 mm.

How Chicago compares inside United States

Philadelphia is about 1069 km away: Chicago is 1.9°C cooler than Philadelphia in its hottest month and 244 mm drier over the year than Philadelphia. Philadelphia’s wettest month is July (124 mm) versus May here.

New York City is about 1146 km away: Chicago is 1.1°C cooler than New York City in its hottest month and 331 mm drier over the year than New York City. New York City’s wettest month is December (133 mm) versus May here.

Manhattan is about 1148 km away: Chicago is 1.4°C cooler than Manhattan in its hottest month and 254 mm drier over the year than Manhattan. Manhattan’s wettest month is October (122 mm) versus May here.