Downpours closed roads and set off flash flooding and a rash of water rescues in Montgomery County. Rain totals up to 3.63 inches were reported in the county Tuesday night, an inch fell in an hour in Pottstown, and the West Branch of the Perkiomen Creek hit flood state, according to the National Weather Service.

But if you wanted to avoid the rain, Philadelphia International Airport would have been your umbrella.

A mere 0.02 inches was captured by the government's official rain gauge on Tuesday, and while airport measurements historically have been problematic, the paltry amount speaks to a persistent pattern of the summer of 2018.

Downpours consistently have deluged areas to the west of Philadelphia, but not so much to the east. Contrasts between rainfall to west of the city and amounts to the east have been dramatic.

"It's crazy," said Dave Dombek, a meteorologist for State College, Pa.-based AccuWeather. Earlier in the summer, the western flank of fair-weather high pressure over the Atlantic shunted rainfall to the west and provided a measure of protection for areas from the I-95 corridor eastward, he said.

But that hasn't been the case in August, and why the rains have kept targeting the same corridor is a mystery.

"There's no particular explanation," said Alex Staarman, a meteorologist at the National Weather Service office in Mount Holly.

One hypothesis is that the early season wetness is begetting wetness — all that evaporating moisture keeps juicing the atmosphere. "There's something to be said about that," Dombek said.

The more likely explanation is "coincidence," said Staarman.

Whatever it is, the numbers are telling.

Wetter to the West

Downpours have consistently creamed areas to the west of the city, and mostly spared areas from I-95 east. Here are rainfall totals by county for the 30-day period that ended Tuesday, and how they compare to long-term averages.
Staff Graphic

In the last 30 days close to 15 inches of rain has fallen on Lehigh and Berks Counties, according to the Middle Atlantic River Forecast Center, which calculates countywide averages using a variety of stations.

Allentown is closing in on a monthly record, and this already has been one of the top five June 1-Aug. 31 periods up that way. State College has clinched its wettest summer, Dombek noted.

Chester County was approaching a foot, nearly triple the average for the period.

Philadelphia hasn't been exactly rain-deprived. The all-city total of 7 inches is well above the 4.3 average.

However, the totals drop off from the airport eastward.

The airport has reported 5.32 inches through Tuesday, roughly the same as Camden County; Gloucester County, 6; and Burlington and Atlantic Counties, 4.8.

Cape May County actually has had below-normal rainfall – 3.5 inches – in the last 30 days. Not that the real estate agents would complain.

And it appears that the region is about to experience several days of dry, decent weather. They won't complain about that either.