Average temperatures (F°) in Chicago
The summers are hot and humid. The winters can be long and stark, inducing the most die-hard riders to bouts of yoga and Netflix binges. The decision to mount fenders is a regular tribulation, regardless of temperature. The tire selection. The layering of kit. Because of the weather, a Chicago cyclist gets to explore every nook and cranny of cycling gear - from tires, to route planning, to electric socks, to waterproof phone protectors.
A note on visibility: Hi-vis clothing is great, but blinky lights (in front and back!) are much more visible. This is a city, so if you're riding before sunrise or after sunset, keep in mind cars can't see you unless you make an effort to be seen.
Chicago's winter has three flavors: cold, really cold, and unbearably cold. While October and November aren't strangers to sub-freezing temps, the temperature usually goes down and stays down in mid-December. January and February are frigid and snowy, and while good long road rides do occur when the roads are clear, deep winter is the time to hit the forest preserves north of the city for some fat bike action or to log miles on a trainer. All that said, the lakefront path in the city is impeccably-well maintained in the winter (if heavily salted) and offers stunning views of a violent, slushy lake.
What to wear: Layer up, buttercup. Up top you'll need some face, ear, and neck protection because wind chills can be brutal. For your hands, bar mitts are excellent, and mittens or lobster-claws provide much better protection for your digits than gloves. For your body, merino wool base layers coupled with a windproof, insulated jacket are a good idea. Clad your cannons in insulated, windproof tights. Insulated boots are recommended, though roomy MTB shoes coupled with thick socks (extra points for heated inserts) and shoe covers will
Spring in Chicago can be described as moist, gusty, and variable. Temperatures are typically in the 40's until late-April although stretches of warmth aren't unheard of. Chicago cyclists are a hardy bunch though, and so long as the winds aren't too rough, group rides and commuters are out in full force. Riding along the lakefront can be exhilarating, and it's not unheard of to battle the wind heading south in the morning only to find the that it's completely changed course to battle you on the journey back up north. So be it.
What to wear: Light base layers like Castelli's Belgian base are excellent - they protect the core in the wind, but have some light cotton venting to keep the cycle-sweats at bay. Knickers or full-length tights are suggested for the cannons, as are arm warmers and some light (water-resistant) gloves. The key here is layers that you can shed once you're warmed up. If it's damp, shoe covers are your friend, as well as a light rain jacket (the kind that folds up nicely into a jersey pocket). Finally, pack a handkerchief or paper towel to wipe down your glasses and face.
Summer in Chicago. It's like a song. The city springs to life with block parties, festivals, lush parks, and throngs of people headed to the lakeshore to enjoy the city's best feature: its miles of sandy beaches. It's the best time of the year for cycling because of the super early sunrises (high-powered, pre-traffic group rides starting just north of Chicago, in Evanston) and fantastic opportunities to do incredibly silly but entirely reasonable things like riding to Milwaukee for lunch and post-ride ales at Café Benelux then hopping on a train back to Chicago.
What to wear: Temperatures range from the 70's all the way to 100+. Humidity is also a major player in the summers - so much so that, mid-ride, someone may proclaim "It's friggin' raining but the sky is blue!" when, in fact, the trees are simply dripping from the moisture in the air. Dressing for the ride is pretty simple: jersey and shorts. Also, slather yourself up with some sunscreen as the mid-day sun can get crispy.
Autumn in Chicago is romantic as heck. The temperatures typically stay mild until mid-October, which means the riding is really, truly pleasant. By this time, the city's 700+ cyclocross racers are gearing up for the season, which starts in September, which means group rides are getting shorter and faster, and plenty of shredders can be seen putting in some 'cross training at Montrose harbor (the location of the Illinois State Championship Cyclocross races). The rides north of Chicago are a particular delight, as the changing color of the leaves coupled with the views of the lakefront can lull you all the way to the Wisconsin border and back before you even scream for a doughnut.
What to wear: Anticipate temperatures ranging from the 50's in the morning up into the high-70's. It may get gusty, so a light base layer for the core is recommended, along with arm and knee warmers to match the short-sleeve jersey and shorts. Depending on your pace, you'll be shedding layers during in autumn more than any other Chicago season.