What to expect for the Philadelphia Marathon weekend weather forecast

Assuming the sports scientists have it right, the temperatures should be near the performance sweet spots for the runners participating in the Philadelphia Marathon Weekend races on both Saturday and Sunday morning.

At showtimes, 6:55 a.m., just moments after daybreak, temperatures Saturday are expected to be in the upper 40s to near 50 degrees for the half-marathoners, and in the upper 30s to around 40 for Sunday’s main event.

Light rain is expected through the early-morning hours Saturday, and forecasters have been on the fence about when it will shut off. Nick Guzzo, a meteorologist at the National Weather Service said Friday afternoon that rain was likely at the start of the race, but that probabilities would drop precipitously once the event was underway.

AccuWeather Inc. and weather.com were posting about a 50-50 shot that the rain would continue through the morning. The hedging isn’t surprising; timing the onset and end of precipitation has been a longstanding forecast problem.

Nor would it be surprising for those running the 13.1-mile race to experience conditions different from those logging 26.2 miles the following day, points out Kathleen Titus, the race director and runner who has been involved with the marathon for 20 years.

This time of year is a busy one for frontal passages, this being a transition period when the atmosphere isn’t quite sure what season it wants to be. The temperature has reached 74 degrees on Nov. 22 (1883), and plunged to 14 (1880), and snowed 4.6 inches on Nov. 22-23, 1989.

However, nothing momentous is expected this weekend.

Like the rains, winds are forecast to be light, under 10 mph, from the north on Saturday, and northwest on Sunday, although runners allow that on the course, the wind can be way more capricious than the temperatures.

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Various studies have concluded that temperature is the most important weather variable in runner performance and that the ideal range for marathoning is 39 to 50 degrees Fahrenheit — give or take a few degrees.

“Your body is always competing between a couple of different things,” said Philip Skiba, sports medicine specialist at Thomas Jefferson University Hospital, who helped train Eliud Kipchoge, the Kenyan who became the world’s first runner to complete a marathon in under two hours.

During exercise, muscles demand blood to work, while for the body to stay cool, blood has to flow to the skin. If it’s too hot, more blood flows to the skin. When it’s cold, blood is diverted to heat the body’s core.

With temperates in that 39-to-50 range, the blood flow can more easily serve both the muscles and skin. Said Titus, racers love that temperature range because, “It regulates your body. It just works.”

Skiba said the temperature ranged from 51 to 55 degrees on the October 2019 day Kipchoge broke the two-hour barrier in a Vienna event that wasn’t held under record-eligible conditions.

Had the temperatures been lower, Kipchoge could have shaved a few more seconds off his time, Skiba said.

While not as dominant as temperature, “wind resistance … is worth a few seconds per mile,” said Skiba, a former triathlete.

“The more you stay out of the wind, you can save considerable energy,” he said.

“It’s really important to learn how to draft,” that is, get behind a group running close to your pace and using them for wind-breakers, he said. (Not sure how the wind-breakers feel about that.)

On the Philly course, the winds can be wild cards, especially on Kelly Drive, Titus said.

One instant, the wind “hits in your face. Now it’s at my back!”

Titus said she actually likes running uphill into the wind — and she is believed to be a member of a distinct minority — but agrees that “it is nice to have it at your back when you’re coming into the home stretch. Because it does give you a little boost.”

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Titus said she is hoping for a record this year, unrelated to race times.

She encourages people to overdress to stay warm before the running gets underway, and to be liberal about peeling off layers during the race.

The shed garments are collected and given to the Salvation Army.

“We’d love to break some record in the clothing donation,” she said.