The short answer
Boston Marathon weather history from 2015 to 2024 swings widely. The air at the 10:00 start ranged from 3.2 °C (38 °F) in the cold rain of 2018 to 21.1 °C (70 °F) in 2017. Of nine race days, three rated Good, four Fair for warmth and two Tough for cold rain.
Key takeaways
- Boston's start air ranged from 3.2 °C (38 °F) in 2018 to 21.1 °C (70 °F) in 2017.
- April race-day air is usually dry; the October 2021 race was the most humid.
- Sun matters: in 2024 the air reached 21.2 °C (70 °F) but felt like 28.4 °C (83 °F).
- Plan for both cold rain and warm sun until the forecast narrows it down.
On this page
- What does Boston Marathon weather history show?
- What was the weather at each Boston Marathon from 2015 to 2024?
- How does the Boston course change your pace?
- How hot does Boston get at your finish time?
- How should you plan your Boston race morning?
- How can you check Boston weather at your own pace?
- Questions runners ask
- Sources and method
Words this guide uses
- ERA5
- The Copernicus reanalysis of past weather, hourly, on a grid about 31 km (19 miles) apart.
- WBGT
- Wet-bulb globe temperature, a heat-stress number combining air temperature, humidity, sun and wind.
- Feels like at running pace
- The temperature your body senses while running, including the airflow you create and the sun on you.
What does Boston Marathon weather history show?
Boston Marathon weather history is a story of extremes. In the nine race days from 2015 to 2024, the start ranged from near-freezing rain to warm sunshine. Our marathon weather history hub compares Boston with London, Berlin and Comrades.
The numbers below are our own. We took hourly ERA5 weather at the real date and start time, then timed it to a runner along the course. That makes a pace-timed forecast run backwards: the weather for each stretch of the course at the time you would have run it.
| The race at a glance | Boston Marathon, USA |
|---|---|
| Date | Patriots' Day, the third Monday of April |
| Start time in our data | 10:00 (09:00 in October 2021) |
| Distance | 42.2 km (26.2 miles), Hopkinton to Boylston Street |
| Climbing | About 135 m (440 ft) up and 270 m (885 ft) down |
| Finish times on our race page | 2:30 to 6:30 |
What was the weather at each Boston Marathon from 2015 to 2024?
Two cold, wet years, four warm ones and three good ones. The table shows each race day for a four-hour finisher, at 5:41 per km (9:09 per mile).
| Date | Start | Air at the start, °C (°F) | Warmest air, °C (°F) | Highest dew point, °C (°F) | Peak WBGT, °C (°F), level | Rain, mm (in) | Rating |
|---|---|---|---|---|---|---|---|
| 20 Apr 2015 | 10:00 | 7.1 (45) | 8.1 (47) | 5.4 (42) | 8.3 (47), Low | 2.4 (0.09) | Tough |
| 18 Apr 2016 | 10:00 | 19.3 (67) | 21.1 (70) | 3.1 (38) | 18.8 (66), Moderate | none | Fair |
| 17 Apr 2017 | 10:00 | 21.1 (70) | 22.9 (73) | 8.6 (47) | 18.7 (66), Moderate | none | Fair |
| 16 Apr 2018 | 10:00 | 3.2 (38) | 8.0 (46) | 7.2 (45) | 8.6 (47), Low | 12.4 (0.49) | Tough |
| 15 Apr 2019 | 10:00 | 13.8 (57) | 18.7 (66) | 13.3 (56) | 18.3 (65), Low | 0.4 (0.02) | Good |
| 11 Oct 2021 (autumn race) | 09:00 | 15.7 (60) | 20.7 (69) | 15.7 (60) | 21.6 (71), Moderate | none | Fair |
| 18 Apr 2022 | 10:00 | 9.0 (48) | 12.3 (54) | −2.2 (28) | 12.6 (55), Low | none | Good |
| 17 Apr 2023 | 10:00 | 11.3 (52) | 12.6 (55) | 11.4 (53) | 13.9 (57), Low | 1.8 (0.07) | Good |
| 15 Apr 2024 | 10:00 | 14.9 (59) | 21.2 (70) | 9.3 (49) | 19.7 (67), Moderate | 0.1 (<0.01) | Fair |
There was no Boston Marathon on the course in 2020. The 2019 WBGT of 18.3 rates Low because the unrounded value sits just under the Moderate line.
This is reanalysis, not a thermometer at the start line. ERA5 gives hourly values on a grid about 31 km (19 miles) apart, so a sunny street or a sea breeze near the finish can differ by a few degrees. It matches the reports where we can check. WGBH describes 2018 as temperatures in the 30s and 40s °F, with wind-driven rain; our data runs from 3.2 to 8.0 °C (38 to 46 °F).
How does the Boston course change your pace?
It's net downhill, with its hardest climbs late. In our course profile, the first 6 km (3.7 miles) drop about 83 m (272 ft) from Hopkinton, which tempts runners out too fast.
The Newton hills then climb about 46 m (151 ft) between km 26 and km 34 (miles 16 and 21), ending at Heartbreak Hill. Then the course falls to Boston. Ely and colleagues (2007), who studied Boston among seven marathons, found slower runners lose more time than the leaders as WBGT rises.
How hot does Boston get at your finish time?
Warmer for slower runners, mostly through the sun. On 15 April 2024, here is the same race day at three finish times.
| Finish time | Average pace | Warmest air, °C (°F) | Hottest feels like, °C (°F) | Peak WBGT, °C (°F) | Moderate heat stress from |
|---|---|---|---|---|---|
| 3:00 | 4:16 per km (6:52 per mile) | 20.6 (69) | 26.6 (80) | 19.7 (67) | km 6 (mile 3.7) |
| 4:00 | 5:41 per km (9:09 per mile) | 21.2 (70) | 28.4 (83) | 19.7 (67) | km 4 (mile 2.5) |
| 5:00 | 7:07 per km (11:27 per mile) | 21.4 (71) | 28.0 (82) | 19.7 (67) | km 4 (mile 2.5) |
All three rated Fair. Cold days work the same way: in 2018, a three-hour runner met 8.6 mm (0.34 in) of rain and a five-hour runner 16.0 mm (0.63 in). Our model starts everyone at 10:00, so a later wave meets each kilometre later in the day.
How should you plan your Boston race morning?
Plan for both ends of the range until the forecast narrows it. In this data, Boston has thrown cold rain and warm sun in alternate years.
- Cold and wet: a throwaway layer, a bin bag and gloves for the wait in Hopkinton. Our guide to what to wear for a marathon has more.
- Warm and sunny: a cap, sunscreen and water over your head at aid stations. Start slower than goal pace on the early downhill.
- Humid: check the dew point; above 15 °C (59 °F), as in October 2021, sweat evaporates less. Our dew point guide explains the bands.
Heat illness can strike even on a mild day, the American College of Sports Medicine (2007) warns. Official race flags and medical advice override this article, which is not medical advice. See WBGT for runners for how heat stress is graded.
How can you check Boston weather at your own pace?
Open the Boston race page, pick a year and set your finish time. It shows the air, feels like, dew point and heat stress you'd have met at Framingham, Wellesley, Heartbreak Hill and Boylston Street. In race week, switch to the forecast with our guide to the race day weather forecast.
Questions runners ask
What was the coldest Boston Marathon in recent years?
2018. Our ERA5 data puts the air at the 10:00 start at 3.2 °C (38 °F), and a four-hour runner met 12.4 mm (0.49 in) of rain, with a wet feels like of −3.2 °C (26 °F). WGBH describes that day as temperatures in the 30s and 40s °F, with wind-driven rain and a stiff headwind. It was the coldest race day in our 2015–2024 data for any of the four races.
Why was the 2021 Boston Marathon held in October?
After the 2020 race was run only virtually, the 2021 Boston Marathon moved from April to 11 October. Our model starts it at 09:00. Autumn air was more humid than April's: the dew point reached 15.7 °C (60 °F), the highest in our Boston data, and the peak WBGT was 21.6 °C (71 °F), Moderate. Treat 2021 as an autumn race when comparing years.
Is the Boston Marathon usually humid?
Usually not. In our April race days, the highest dew point along the course averaged about 7 °C (45 °F), well inside the comfortable band below 10 °C (50 °F). It dipped to −2.2 °C (28 °F) in 2022. The muggiest April day was 2019, at 13.3 °C (56 °F). Dry air lets sweat evaporate, which is why Boston's warm years rated Fair rather than Tough.
Why can Boston feel much hotter than the forecast high?
Because of the sun. Weather forecasts give the air temperature in the shade. Running in sunshine, you absorb extra heat from the sun on top of the heat you make. In 2024 the air reached 21.2 °C (70 °F) for a four-hour runner, but the feels like at running pace reached 28.4 °C (83 °F). A hat, light colours and cooling at aid stations help.
What should I wear at the Boston start in Hopkinton?
Dress for the start and plan to shed layers. Starts in our data ranged from 3.2 to 21.1 °C (38 to 70 °F), so check the forecast that week. On cold mornings, a throwaway top and a bin bag keep you warm and dry before the gun. On warm mornings, wear your race kit, a cap and sunscreen. Our marathon kit guide covers both.
Your race, at your pace.
Pick Comrades, Berlin, London or Boston, set your finish time, and see the heat stress, feels like and dew point you’d have met at every landmark, on every race day from 2015 to 2024.
Sources and method
- Copernicus Climate Change Service (ECMWF) (2023). ERA5 hourly data on single levels from 1940 to present
- WGBH (2026). Snow squalls and the 'Run for the Hoses': a brief history of Boston Marathon weather
- Medicine and Science in Sports and Exercise (2007). Impact of weather on marathon-running performance (Ely, Cheuvront, Roberts and Montain)
- American College of Sports Medicine (2007). Position stand: exertional heat illness during training and competition (Armstrong et al.)
- Journal of Occupational and Environmental Hygiene (2008). Modeling the wet bulb globe temperature using standard meteorological measurements (Liljegren et al.)
Every Boston Marathon run on its course from 2015 to 2024 (2020 was virtual only and is left out; 2021 ran on 11 October), at the real date, starting at 10:00 (09:00 in 2021). Weather is hourly ERA5 reanalysis (Copernicus Climate Change Service, ECMWF) at the three 0.25° grid points the course crosses (near Hopkinton, Wellesley and Boston); each stretch takes its nearest point. The RunFast engine times a runner along our 42.4 km course model at an even effort for a 3:00, 4:00 or 5:00 finish, with pace adjusted for gradient, and reads the air, dew point, feels like at running pace, WBGT (Liljegren et al., 2008, with cloud worked back from ERA5 sunshine) and rain at each stretch when the runner is there. WBGT levels: Low below 18.3 °C (65 °F), Moderate to 22.8 °C (73 °F), High to 27.8 °C (82 °F), Extreme above, judged on unrounded values. Ratings: Fair at Moderate heat stress, Tough at High or Extreme, or in cold rain (1 mm or more with a wet feels like of 5 °C, 41 °F, or less). The April dew-point average is the mean of eight April race days at a 4:00 finish. Climbing is measured from the course profile, counting rises of 3 m (10 ft) or more. Fahrenheit and inch values are our conversions. RunFast is independent of the Boston Athletic Association.
Wes Thomson
Wes Thomson builds RunFast, which times the heat, humidity and dew point to a runner's own pace along the route, and its sister Windline, live wind forecasts for cyclists. Both run on the same forecast engine. He writes these guides with one focus: what the weather will do to your run, kilometre by kilometre, and how to plan around it.