Twin Cities Marathon runners warned of extreme heat and humidity for Sunday's race

Organizers of Sunday's Twin Cities Marathon are concerned about one of the few things they can't control: weekend weather that could make this one of the warmest races in its history.

The current forecast of high humidity and warmer-than-average temperatures during the races this weekend prompted Twin Cities in Motion (TCM) to issue an alert to runners. The overnight low Saturday is 67 degrees, according to AccuWeather, and it'll be a bit warmer by the start of the TC 10 Mile at 7 a.m. Sunday, preceding the marathon. Humidity could hit 70% in the morning, with a dew point of 63 degrees.

This wouldn't be the first hot one. At the time, the Twin Cities Marathon on Oct. 7, 2007 was the warmest in the race's history. It was 74 degrees, with 87% humidity at the 8 a.m. start. That same day the Chicago Marathon canceled its race hours into the event, owing to the conditions.

TCM's weather alert in an email Tuesday went to all participants this weekend and was prominent on its website's home page. From the family events, including a 5-kilometer and 10K Saturday, to the marathon, there are about 25,000 entrants.

TCM said it will operate under what's known as red-flag conditions in running circles. Flag conditions span from black (event canceled) to white (risk of hypothermia). This weekend's forecast calls for extreme caution, TCM said in a communication to runners, adding that it is "gathering extra course and finish line resources" for supporting them. The forecast calls for 80 degrees at noon Sunday.

Race director Eli Asch said TCM routinely consults with public safety agencies while planning its events. The organization's medical and operations teams are continuing those conversations this week. Last Tuesday, they began sharing information with runners about how to stay safe in hot, humid conditions.

"Ultimately, this forecast is challenging for both us and our runners," he said, "but we also believe that both we and our runners are prepared for it."

In addition to encouraging runners to arrive hydrated on their race days, TCM said participants should take precautions by drinking more when thirsty out on the courses, and entrants with "previous heat stress problems or heart disease should not start their race."

Tyler Jermann, one of the top runners in the men's professional field, said experience has taught him how to handle the heat. The St. Paul resident plans to run conservatively in the first half of Sunday's race, preserving energy for the second half. By the time runners reach the tough push up Summit Avenue, Jermann hopes to pass athletes who went out too quickly.

A member of the Minnesota Distance Elite training group, Jermann said a hotter-than-usual summer in the Twin Cities also helped prepare him for Sunday's conditions.

"(The heat and humidity) really does make a difference," he said. "If it's 75 and humid, you've really got to adjust five or 10 seconds a mile. It's sneaky when it's humid — you don't think it's affecting you, then all of a sudden, it hits you like a ton of bricks. So I definitely think it's going to be a factor, and something to take into consideration with the race plan."