One soggy weekend is forecast for Philly, but Broad Street runners might dodge the rain

With upward of 100,000 spectators due in town from all over the country, along with 50,000 runners and other athletes, forecasters say the Philly region is about to experience its wettest weekend of what has been an exceptionally dry year.

However, they also say it’s entirely possible that the racers participating in Sunday’s Independence Blue Cross Broad Street Run will dodge the raindrops, and that steady rain will hold off during some of the events at the Penn Relays, which began Thursday and continue through Saturday.

“It may be good news for the runners Sunday morning,” Bobby Martrich, meteorologist with EPAWA, whose clients include the Phillies, said Thursday afternoon. But the outlook for the bulk of the Penn Relays is “iffy,” he added.

Both are rain-or-shine events, and be advised that umbrellas won’t be permitted at Franklin Field, the venue for the Penn Relays.

Participants and spectators may not want to hear this, but with rain deficits placing much of the region in the U.S. Drought Monitor’s “abnormally dry” zone — almost all of Chester County and pieces of Bucks and Delaware Counties in “moderate drought” — Philly could use a decent soaking, said Sarah Johnson, the warning coordination meteorologist with the National Weather Service Office in Mount Holly.

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“Hopefully it doesn’t interrupt too many plans,” she said.

It’s possible that it won’t.

The impending rains would be wrung out from a series of storm systems bookending the weekend.

In the first wave, the heaviest rain is due to hold off until late Friday and Friday night, and it could be quite stormy during the day Saturday with winds past 25 mph. Lingering rain is likely in the morning, but could shut off Saturday afternoon, Johnson said.

The computer models are quibbling, she added, but the lull in the rains could continue into Sunday afternoon, well past the race time, she said.

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For Sunday morning, winds are forecast to be light, blowing from the east, off the Delaware River, with temperatures in the 50s. The National Weather Service, accuweather.com, and weather.com all say that any rain that does fall during the race should be light.

But do expect a 100% chance of sweat as the air will be near saturation, rain or not.

Significant rain is forecast later Sunday into Monday. After the rain stops, the spring chill is forecast to persist, with below-normal temperatures into the first week in May.

Assuming the forecast holds, the rains would continue a trend: Rain has fallen on Saturday and/or Sunday in six of the last seven weekends.

Meteorologists say this isn’t unusual. Given the spacing between systems in the atmosphere, they sometimes get into a rut of arriving in 3- to 3½-day intervals. When that happens, rain on a Saturday or Sunday almost guarantees rain the following weekend.