The Weather

19 years of race day conditions to help you plan your perfect run

52°F

Median Start Temp

10/18

PR-Worthy Days

15-20°F

Typical Temp Rise

6-10 mph

Average Wind

I spent a lot of time with this data before my 2024 race. My start was 51°F and partly sunny, close to ideal, but I still lost a few minutes in the back half to a headwind I hadn't planned for. The range in this table is what gets people. 33°F in 2009, 74°F in 2007. October in Chicago can go almost anywhere, and the difference between a PR day and a survival day often comes down to whether you planned for both.

What This Means for You

✓ The Good News

• About 56% of races have PR-worthy conditions
• Median start is perfect running weather (low 50s)
• Recent years (2022-2025) have trended cooler
• Truly brutal days are rare (but memorable)

⚠ What to Watch

• Humidity and dew point matter more than temp
• Wind direction changes race difficulty dramatically
• October weather is highly unpredictable (28°-88°F range!)
• Plan for 15-20°F temperature rise during race

Chasing a BQ? Weather plays a huge role in your chances. Read the Boston Qualifying Guide →

Complete Weather Archive

Year	Date	Start	Finish	Humid%	Dew Pt	Wind	High/Low	Type	Conditions
2025	Oct 12	53°	68°	65%	42°	8 SE	68/49		Clear, sunny
2024	Oct 13	51°	62°	70%	43°	10 W	67/49		Cool, partly sunny
2023	Oct 8	46°	51°	60%	35°	12 NW	57/45		Cool, mostly cloudy
2022	Oct 9	44°	58°	68%	36°	9 W	69/42		Cool, clear
2021	Oct 10	67°	76°	76%	56°	6 SW	79/63		Warm, sunny
2020	N/A	N/A	N/A	N/A	N/A	N/A	N/A		Cancelled
2019	Oct 13	47°	52°	63%	36°	9 N	55/44		Cool, light rain early
2018	Oct 7	60°	68°	90%	57°	7 S	70/58	◐	Humid, cloudy
2017	Oct 8	57°	72°	73%	51°	6 SW	79/56	◐	Warm
2016	Oct 9	54°	61°	80%	47°	7 W	63/49		Mild, partly cloudy
2015	Oct 11	52°	68°	86%	48°	5 S	79/51	◐	Warm, humid
2014	Oct 12	45°	58°	71%	36°	5 NW	61/43		Cool, clear
2013	Oct 13	45°	58°	66%	36°	4 W	64/41		Cool, partly cloudy
2012	Oct 7	38°	48°	63%	32°	7 NW	51/36		Cool, clear
2011	Oct 9	55°	72°	71%	46°	3 S	80/54	◐	Mild start, warm finish
2010	Oct 10	65°	78°	68%	55°	3 SW	86/57		Hot, sunny
2009	Oct 11	33°	42°	67%	24°	5 W	45/28		Cold, clear
2008	Oct 12	64°	72°	75%	56°	5 SW	86/63		Warm, sunny
2007	Oct 7	74°	82°	81%	66°	6 S	88/65		Hot, sunny

Chicago Wind: Direction Matters

Chicago's flat reputation is misleading. Wind direction dramatically changes your race experience.

North Wind ↓ (Worst)

Headwind miles 1-8 and 23-26.2. Brutal, as you'll battle it for the entire northbound portions, including the critical final push to the finish.

South Wind ↑ (Best)

Tailwind miles 1-8 and 23-26.2. This is generally the most favorable, as you get a significant push for the crucial early miles and the entire final northbound push home. Headwind primarily on miles 8-13 and southern loops.

West Wind →

Crosswind for most North/South segments and headwind for miles 13-15. This creates a persistent crosswind and a direct headwind during the westbound stretch through the West Loop.

East Wind ←

Crosswind for most North/South segments and tailwind for miles 13-15. Generally more favorable crosswind, with a helpful tailwind during the westbound stretch through the West Loop.

Wind Pattern History

18 years (2007-2025)

West/NW

39%

South/SW

33%

North

6% - Worst

East/SE

6% - Unicorn!

What to Expect

72% chance of westerly or southerly winds. Prepare for crosswinds or early headwinds. True tailwind finishes are extremely rare.

What to Wear Based on Conditions

Temp Range	Top	Extras	Notes
30s-40s°F	Long sleeve or short + arm sleeves	Gloves, beanie, trash bag poncho	Disposables you can toss at mile 3
50s°F	Short sleeve tee (maybe singlet)	Arm sleeves, light gloves	Sweet spot - dress like it's 15° warmer
60s°F	Singlet or light tee	Nothing	Stay light, hydrate more
70s°F+	Lightest gear possible	Hat with ice, sunscreen	Survival mode - adjust pace expectations

How to Adjust Your Race Plan for Weather

Warm Days (60°F+ at start)

• Slow your pace 10-20 sec/mile from the start
• Drink at every station, even if you don't feel thirsty
• Pour water on your head after mile 13
• Skip the early surge - save energy for survival mode
• Accept a slower time - DNF is worse than a "slow" finish

Cold Days (Below 45°F at start)

• Warm up longer before the gun
• Don't overdress - you'll heat up fast after mile 3
• Bring throwaway layers for the corral
• Cold = fast - consider a PR attempt if trained
• Watch for ice in shaded areas early (rare but happens)

Humid Days (Dew point 55°F+)

• This is sneaky brutal - temps lie, dew point doesn't
• Sweat won't evaporate - you'll overheat faster
• Extra hydration critical
• Slow down more than you think you need to
• Salt tabs or electrolytes become more important

Windy Days (12+ mph)

• Check wind direction - it changes everything
• Headwind = shelter behind taller runners when possible
• Tailwind = free speed, but don't blow up early
• Crosswind = just grit your teeth and lean slightly
• Add 30-60 seconds to your projected finish in strong wind

The Legendary Years

2025: American Record Falls

53°F start, clear skies, light southeast wind. Near-perfect conditions. Conner Mantz broke the 23-year-old American marathon record (2:05:38) with a 2:04:43 finish. Jacob Kiplimo won in 2:02:23. The kind of day that makes Chicago legendary for fast times.

2007: The Meltdown

88°F high, 81% humidity, dew point in the mid-60s. Race organizers halted the event at 3.5 hours. One death, over 400 treated for heat-related issues. This is the day that changed marathon safety protocols nationwide. Start temp was 74°F - already brutal.

2009: The Deep Freeze

33°F at the start, high of just 45°F. One of the coldest Chicago Marathons ever. But it was also fast - low humidity, no wind, perfect conditions if you dressed right. Proved that cold beats heat every time.

2023: The Record Breaker

46°F start, stayed in the low 50s. Kelvin Kiptum ran 2:00:35, coming within 35 seconds of breaking 2 hours. Near-perfect conditions - cool, dry, light wind. The kind of day runners dream about.

2019: Rain & Records

47°F start with light rain early. Rain cleared by mid-race. Brigid Kosgei broke the women's world record (2:14:04). Rain didn't slow anyone down - cool temps and low dew point made it fast.

2025 Race Recap

Sunday, October 12, 2025 ✓

Another fantastic PR day!

Start Temp

53°F

High

68°F

Wind

8 mph SE

Conditions

Clear ☀️

Jacob Kiplimo 2:02:23 (men) - Hawi Feysa 2:14:56 (women) - Conner Mantz broke American record!

Weather Tips for Spectators

If you're cheering, not running, weather prep is just as important.

• Hot days: Bring ice towels, extra water, and sunscreen
• Cold days: Hand warmers, hot coffee, and layers
• Rain: Skip umbrellas (blocks views), bring ponchos
• Windy days: Secure your signs and dress warm

View Full Spectator Guide →