Strong storms likely later Friday; flash flood watches posted

The entire region is under a severe thunderstorm watch until 10 p.m., with the government's the government's Storm Prediction Center has placed the region under a severe thunderstorm watch until 2 p.m, warning of potential gusts past 60 mph.

And with the ground about as soggy as a sheet cake left out in the rain, the National Weather Service has posted flood watches  for those parts of the region that have been pestered all week with episodic heavy rains.

The high levels of water vapor and the atmosphere's energy look ripe for setting off storms that could produce potent gusts, the National Weather Service says. The most-likely window for mayhem would be from 6 p.m. to midnight.

Thunderstorms already have hit parts of upper Bucks and Montgomery Counties, where flood advisories are in effect.

Daytime heating — temperatures are approaching 90 in Philadelphia — could give any storms an additional kick.

With the ground about as soggy as a loaf of bread left out in the rain, some flooding isn't out of the question, said Alan Cope, science and operations officer at the National Weather Service in Mount Holly.

"A lot of the ground is still pretty saturated, so we're still concerned about localized flooding," he said.

But the Schuylkill and the Delaware River are forecast to stay well within their banks. The Susquehanna climbed above flood stage Thursday in Harrisburg — perhaps related to moisture plumes from the Chesapeake Bay — but the local rivers generally have been well-behaved.

Coming into the sog-a-thon, the region had been generally dry. And for all the tumult this week, remarkably officially Philadelphia's rainfall for July remains below normal – just over 2.9 inches through Thursday, compared with 3.65, the normal through July 25.

In the last week, over 4 inches has been measured in Chester County, based on measurements at countywide rain gauges, according to the Middle Atlantic River Forecast Center.

By comparison, only 1.38 inches fell upon Philadelphia through Wednesday, and 1.27 on Camden County.

Forecasters say that high pressure over the Atlantic has blocked movement of all this moisture but that its western flank has provided a measure of protection from I-95 east, not that it's been a week in San Diego along the I-95 corridor.

"The heaviest rain certainly was to the north and west," Cope said. The deluges inundated the lower and middle Susquehanna with a particular ferocity, said Cope, and that rainfall probably was enhanced by winds from the south blowing over the Chesapeake.

In addition to Friday's expected rain, showers are back in the forecast for early next week; however, another prolonged siege of tropical-like rains and dropped ceilings isn't expected.

"The pattern has changed," Cope said. "So we don't have that long fetch of flow out of the tropics."

In the meantime, all the moisture also has provided a measure of protection from one of summer's less welcome visitors: heat.

This is the season for atmospheric caprice, but no 90-plus temperatures show up in forecasts for the next 10 days.

"We're not looking at any major heat waves in the near future," Cope said.