2018 Boston Marathon: Runners may encounter cool, wet conditions

No matter how long runners have trained, weather is always the one variable that remains out of their control.

Despite whatever challenges Mother Nature throws at them, more than 30,000 runners will race 26 miles to the finish line of the 122nd Boston Marathon on Monday, April 16.

AccuWeather Senior Meteorologist Kristina Pydynowski said there will be seasonable temperatures along with the threat of rain.

"Depending on the track of the storm delivering the rain, thunderstorms may also be a threat to runners and spectators. Pydynowski said.

A normal high for April 16 in Boston is 56 degrees Fahrenheit and a normal low is 41.

Morning temperatures will be in the mid-40s and afternoon temperatures are expected to reach around 50. Winds will blow out of the west at 10-20 mph with gusts reaching 30-35 mph, according to AccuWeather Meteorologist Bob Smerbeck.

A cold and active pattern from March is still continuing, but it looks like an end is in sight.

"A cool front will move eastward through Boston the night before with rain, then clouds will break for sun and a gusty wind behind the front on marathon day. A slower arrival of the front could cause rain to linger for the race," Smerbeck said.

The race is broken up into multiple classifications. The first group on the course consists of mobility impaired racers, who will start at 8:40 a.m. The men's elite runners and first wave of participants will start at 10 a.m., about 20 minutes after the women's elite runners. The last wave of participants will begin at 11:15 a.m.

AccuWeather is forecasting a gusty west wind so runners will have wind at their backs, which could potentially help them.

Related: Look back at last year's race:

Calm and breezy weather conditions haven't always been the case for Boston Marathon runners.

"The early part of the 20th century had a high number of extreme weather conditions for the race, both hot and cold," Smerbeck said.

Michael McGrane, who is the Boston Athletic Association's (BAA) Running Club coach and has run the past 17 Boston Marathons, said he has experienced many types of inclement weather.

"I think I have experienced a good range of weather conditions over the past 17 years including two years when it hit 90 degrees and the nor'easter year," McGrane said.

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"The ideal temperature for a marathon is in the range of 50 to 60 F with low humidity and light to no winds. For the Boston Marathon in April, the sun can be more intense and there is very little or no shade on the course at this time of year so it's ideal to have an overcast or cloudy weather day," McGrane said.

Some of the worst marathon weather happened most recently in 2004 and 2012 when the temperatures hit 90 F on marathon day.

When the temperature exceeds 65, a runner's performance in the marathon can begin to decline due to dehydration, McGrane said.

"The last two years the temperature has been 70 and most of the marathoners from our BAA Running Club were five to 10 minutes slower than their goal time due to the warm and sunny day. The other extreme was in 2007 when a nor'easter threatened to halt the 2007 Boston Marathon," McGrane said.

Related: Look back at winter weather that has plagued New England:

According to McGrane, in colder weather, especially when it rains, runners struggle to keep warm and muscles often tighten up, which can slow their pace.

"Wind is another weather factor that can slow a runner's time in a marathon. A headwind can slow a runner's marathon time by five to 15 seconds per mile by creating a force against the runner, whereas a tailwind can improve a runner's pace by five to 15 seconds per mile running with less effort required," McGrane said.

The Boston Marathon is well known to feature variable weather.

"In April in New England, if it's a cold marathon day then it's often a slight to significant headwind with the wind coming off the cooler coastal waters. If it's a warm day, then it's often a tailwind with the warm southwest wind. On a rare perfect marathon day, as was the case in 2011, the weather is cool with a tailwind," McGrane said.

According to McGrane, it happens maybe once every 10 years.