The Broad Street Run might have its chilliest start ever, but it’s likely to be dry

The annual Independence Blue Cross Broad Street Run almost certainly will get off to one of its chilliest starts in its 46-year history, and maybe even the chilliest.

Temperatures at the 7 a.m. race time are forecast to be in the mid-40s with just a way outside chance of a lingering shower, said Robert Deal, a runner and the science and operations officer at the National Weather Service office in Mount Holly.

The lowest official start temperature, as measured at Philadelphia International Airport was 47 degrees, in 2016. It was 50 two years ago, but has not been in the 40s since 2016.

Studies suggest that the temperature and other atmospheric factors during the race should be ideal for racing, but not necessarily for other activities; for example, watching.

Winds from the northwest just under 10 mph will make it feel slightly chillier, but it would be more or less a tailwind for the runners.

The conditions would be more typical of the March Love Run or the city’s annual marathon in November, said Seth Weiss, head of the Philly Runners club, a 20-time veteran of the Broad Street Run who will be one of the 40,000 participating Sunday.

“I think it’s good conditions for running,” he said, but not good for the club’s traditional post-race outdoor barbecue. This year he moved it “inside to a local restaurant ... I thought it would be too cold to be enjoyable.”

May mornings have been trending warmer, in step with the increases in the planet’s temperature.

By the weather service’s calculation, the normal daily low temperatures for the month, typically reached around daybreak, are 1.7 degrees Fahrenheit higher than they were in 1980, the first year of the race.

The normal lows this time of year are in the low 50s in Philadelphia. However, this would not be the first time in recent years that they would have fallen into the 40s, as winter isn’t all that far away in early May.

The race is traditionally held on the first Sunday in May, on dates ranging from May 1 to May 7. On multiple occasions, the race has sidestepped the chilliest days during that seven-day window. It dropped into the 30s the first week of May in 1986, but at race time on May 4 — 9 a.m. in those days — it was 48. The later starts in those days gave the temperatures a chance to warm up under the May sun.

Aside from the more-than-occasional chill, the runners have endured their shares of rain and assorted unpleasantness.

A case in point would be the 2023 race, which was held on April 30, 2023, in deference to the Phillies, who were hosting the Boston Red Sox on the traditional race Sunday.

The racers ran in chilly rain; a week later, the Phillies played in the sunshine. (By the way, the Phillies that day snapped a six-game losing streak. Kyle Schwarber broke an 0-21 slump and hit a homer after being booed. The winning pitcher was Taijuan Walker.)

In a study of nearly 2 million marathon participants in the United States, England, Germany, and France, a team of French sports-medicine specialists concluded that the ideal distance-racing temperature was about 44 degrees Fahrenheit.

Another analysis that examined more than 1,200 races, ranging from 3 miles to marathons, in 42 countries, looked at another indicator, the “wet bulb globe temperature,” which takes into account traditional temperature, moisture in the air, winds, latitude cloud cover, and the angle of the sun.

The ideal reading on that scale for runners would be 50.

That happens to be the wet bulb globe temperature forecast for 7 a.m. Sunday.

That’s all well and good, but as someone who has nothing to prove, the weather service’s Deal said he prefers more warmth and moisture in the air since it makes easier breathing for him. He will not be racing Sunday.

“I would say by no means am I a marathoner,” he said, “and by no means am I fast.”