Half of a million people will pack the streets of Boston on Monday, April 18 to cheer on 30,000 runners in the 120th Boston Marathon.
"It looks like Monday will offer ideal conditions for the runners this year," AccuWeather Meteorologist Maggie Samuhel said.
Skies will be dry and conditions will be mild with temperatures starting out near the 50-degree-Fahrenheit mark as the first wave of runners begin. Highs will approach the low 60s in the afternoon.
Cloudy skies could offer some relief to the runners and a dew point in the 40s will yield comfortable conditions.
The week leading up to the race will be dry due to a high pressure system sitting over the region. There is a chance a clipper system dropping south from Canada could break that up and bring showers to Boston on Monday, Samuhel said, but dry conditions will likely hold strong.
While every runner has different preferences, milder conditions are usually better, Brian Dalek, digital editor at Runner's World, said.
"Most people will be happy with something in the 40- to 50-degree range, a little cloud coverage to block out the sun in your face and low wind so you don't have another obstacle to deal with," Dalek said.
The unique course that stretches from Hopkinton to the John Hancock Tower in downtown Boston offers little shade, making cloud cover a key factor.
Eight-time Boston marathon runner and Chief Running Officer for Runner's World Bart Yasso told AccuWeather that the first time runners feel shade is when they cross the finish line.
Though spectators may not welcome any precipitation, light rain can be refreshing for some runners.
Heavy downpours may lead to challenges, Dalek said, like during the 2015 race. An unusually high number of participants were treated for hypothermia last year amid drenching rain and cold conditions, according to WBUR.
Strong winds also create grueling conditions, often hindering momentum if it's a headwind, Dalek said.
"Boston is something a majority of marathoners train their whole lives for," Dalek said.
Intense training typically starts 14 to 16 weeks before the race date once a spot has been secured.
"This includes building up your mileage over several weeks, hitting a peak in training, then taking the last couple weeks to taper so you feel fresh heading into the race," he said.