The atmosphere evidently is preparing a welcome back gift for the 27,500 people who will be participating in the Blue Cross Broad Street Run on Sunday morning, when one of the region’s most popular events revives its spring tradition for the first time since the pre-COVID era.

Temperatures at the 7:55 a.m. race starting time are expected to be in the upper 40s with a paltry 4% chance of any rain, the National Weather Service said.

The blustery winds that drove wind chills into the 20s in the region on Thursday and Friday mornings will have yielded to a gentle 1-mph tailwind from the north Sunday morning, the National Weather Service says. That might even add an extra step for the runners along a course that begins at Broad Street and Fisher Avenue and descends about 100 feet by the time it ends at the stadium complex.

Study findings suggest that both the temperature and a more complicated measure that takes into account other factors such as wind and atmospheric moisture should be in performance sweet spots.

» READ MORE: Everything you need to know about the return of the Broad Street Run

“It should be real good for the runners,” said Jonathan O’Brien, a meteorologist at the National Weather Service Office in Mount Holly. “I don’t think you could ask for a better Sunday morning.”

The race organizers, who have been monitoring the forecasts closely, stopped short of complaining. “We’re all so excited,” said Maita Soukup, spokesperson for Philadelphia Department of Parks and Recreation, which is organizing the run. “Perfect weather conditions!”

She added that an additional 900 runners plan to compete “virtually.”

The in-person race was canceled in 2020, and last year the event was moved to October and became “hybrid” for the first time; that is, with both in-person and virtual participation.

So this is somewhat of a homecoming for the venerable race, for which this would be the 42nd running. But the city is discouraging spectators from showing up and cheering on the runners.

» READ MORE: Catching COVID outdoors is unlikely. So why are Broad Street Run spectators asked to stay home?

Not that anything has been normal since March 2020, but in “normal” years, the race typically drew thousands of onlookers.

This time around the runners at least should have the atmosphere cheering them on.

» READ MORE: How the Broad Street Run times thousands of runners at once

At least two studies show that temperature is the most important variable affecting performance. An analysis published in 2012 in the journal PLOS One regarding 1.8 million marathon participants in Boston, Chicago, New York, Paris, London, and Berlin of elite and not-so-elite runners concluded that 44 degrees Fahrenheit was the ideal temperature. That’s not far off Sunday’s forecast.

A 2021 study involving researchers from Greece, Denmark, Australia, and Qatar looked at the effect of what is known as Wet Bulb Globe Temperature, an index computed by a complicated formula that includes air temperature, atmospheric moisture, cloud cover, and winds. The weather service has used it, but not in public forecasts.

» READ MORE: Scenes from the October Broad Street Run

The WBGT forecast for race time (53 degrees, if you must know) would be right within the optimal range for peak performance that the researchers identified.

As a bonus, the post-race weather will be decent, with light winds and sunshine into midafternoon and highs approaching 70.

But then, it appears, our dry run will be coming to an end.

The forecast is calling for an outside chance of showers late in the afternoon and evening, but Alex Staarmann, meteorologist at the weather service Mount Holly office said Saturday, “I think any showers should hold off until the overnight period.”