On April 17, more than 32,000 runners will race 26 miles to the finish line of the 121st Boston Marathon.
Athletes participating in the world’s oldest annual marathon can expect to race in cooler weather with temperatures reaching 55 degrees Fahrenheit and winds up to 15 mph.
In addition to a cool flow from the north, a partly cloudy sky will provide some shade for runners throughout Monday morning.
“A little bit of cloud cover is a big help, because there’s no shade on the Boston Marathon course until you finish,” said Runner's World Chief Running Officer Bart Yasso.
As runners beginning the race in Hopkinton and head east toward the finish line on Boston’s Boylston Street, they can expect to encounter cooler air coming from the Atlantic Ocean.
“Of course, there’s no such thing as a cool marathon,” said AccuWeather Chief Meteorologist Elliot Abrams. “If you run that distance, you’re going to be perspiring. The worst ones are when it rains or it’s either around 80 degrees and high humidity – it gets very steamy,” he said.
Monday’s high of 55 F should appease the majority of runners, who typically tend to favor cooler weather around 50-55 degrees with low humidity, according to Yasso.
It is likely to be a dry morning for runners, with humidity predicted to hover around 51 percent.
While Monday’s forecast may not be ideal for every runner, Yasso said it’s still crucial for athletes to be prepared to encounter a variety of conditions.
In general, the weather in Boston and the surrounding areas changes often during mid-April.
“There’s no such thing as scripted weather, but you have to adjust,” Yasso said.
As the marathon’s history has shown, sometimes even the utmost preparation can be thwarted by an unexpected change in weather.
In 1976, runners raced during one of the hottest Boston Marathons on record, facing scorching temperatures of 96 F for much of the first half of the course.
In stark contrast, temperatures were in the mid-40s with gusts around 15 mph during the 2015 Boston Marathon, according to the Boston Athletic Association.
Many runners required medical treatment for hypothermia due to cold and rainy conditions, said certified running coach Nick Joannidis, a three-time Boston Marathon participant.
“Wind in any direction, rain, snow and humidity are all other factors that impact race conditions,” said Joannidis, whose running career spans more than 30 years.
“These are all exacerbated by other factors such as a runner's age, sex – women are more prone to hyponatremia, [which is caused by] drinking too much water during a long athletic contest – conditioning, injury history and consuming too few electrolytes during the race,” he said.
Training in a different climate than where the race takes place is another factor for runners to consider.
“You can be living in a very warm climate through training and be wearing shorts and sleeveless tops, and then you get to Boston and it’s 45 degrees,” said Mindy Solkin, professional running coach and founder of The Running Center. “You have to change up a bit.”
Monday’s forecast shows only a slight chance of rain.
When rain is expected during a marathon, the key is for runners to remain as dry as possible before the start of the race.
This helps the runners’ bodies produce heat once they begin running.
“The worst thing is to be cold at the start, and that’s what you have to avoid,” said Yasso. “Your body starts shivering when you’re cold; it’s burning energy to keep you warm.”
Even in the absence of record-setting temperatures this year, the 121st Boston Marathon will still be a historic event.
Among the tens of thousands of athletes will be Kathrine Switzer.
The athlete will run the race for the first time in 50 years after being nearly yanked off the course by a marathon official due to her gender in 1967.
AccuWeather.com will continue to update the Boston Marathon forecast with the latest information in the days leading up to the race.