Philly’s recent rainfall is way above normal. Here’s how much has fallen.
The rains have been capricious, but overall Chester County had 17 times more rain in seven days than it had in all of May.
In a period when thunder has become the Philadelphia region’s unofficial soundtrack, those accompanying downpours have had at least one benign effect: They’ve staged an all-out attack on what had become worrisome rainfall deficits.
After an all-night light show when it seemed that jittery lightning was flashing across the sky like so many malfunctioning electric signs, the National Weather Service reported some prodigious rain totals Tuesday.
Around 5 inches was measured in northern Delaware, and close to 4 in Downingtown, Chester County. That came atop a sequence of storms that ripened during the weekend, and before a fresh round of potent storms later Tuesday that prompted a flood watch, and flood warning for parts of the region.
» READ MORE: Another flood watch was hoisted on Tuesday
In the seven-day period that ended Monday, Chester County had 17 times the amount of rain as in the entire month of May, according to figures from the Middle Atlantic River Forecast Center.
» READ MORE: Here's what's behind the change in rain fortunes
The rains, however, have had a distinct lottery-ball nature. For example, only about an inch fell in Chester Springs Monday into Tuesday morning, only seven miles from Downingtown. A total of 4.35 inches landed in the gauge at New Castle Airport, and just 1.25 at Philadelphia International Airport’s.
Bizarre? No, said Kristen Kline, hydrologist at the Middle Atlantic River Forecast Center, in State College. That’s the nature of rain in June, when the steering winds that move storms appear to succumb to the muggy, languid air and lose their senses of direction like so many of the rest of us.
“With these type of showers you do expect rainfall totals to vary even in short distances,” she said.
That has decidedly been the case the last few days. Some areas were inundated with waterfall-like showers Saturday and Sunday. Yet the total at PHL on Saturday was 0.02 inches, and 0.09 on Sunday.
To present a more-coherent picture of regional rainfall, the river center, a division of the weather service, uses a sampling of stations to calculate countywide totals in weekly, monthly, and annual increments.
Its figures show just how wet the last week has been, and also why Pennsylvania was still under a drought watch as of Tuesday.
Yes, as of Tuesday, all of Pennsylvania remained under a drought watch that went into effect June 15. The reason, in a word, is May.
» READ MORE: The drought watch that went into effect June 15 remains
The river center data showed that last month, Philadelphia and its four neighboring Pennsylvania counties received about 5% of their normal rainfall.
The wettest of the counties, Bucks, received a thimble-size 0.4 inches, or less than a fifth of what was measured there in the last week.
The five counties averaged about a quarter-inch for all of May, and 2.6 inches, or 10 times of much, in the seven-day period ending Monday.
About the rains
Meteorologists say the region’s rain fortunes took a radical turn late last week, about the time that the atmosphere swelled with something akin to a toxic soup of water vapor.
An upper-air pattern that resulted in quite a cool and arid May into June relented, allowing humid air from the Gulf of Mexico to pulse northward.
The conditions haven’t been all that unusual for late June, but the contrast to the antecedent weather clearly added to the discomfort. That muggy air became a rich source of moisture for incipient thunderstorms.
Rain falls as warm air soars over cooler air in the higher atmosphere, and the lightning and the cloudbursts were the functions of tremendous updrafts, rocketing up to 50,000 feet, said Cameron Wunderlin, a meteorologist with the National Weather Service in Mount Holly.
In all, Peco reported over 95,000 power outages Monday into Tuesday.
Meteorologists say the storm traffic is about to back off considerably, with only a slight chance of showers Wednesday and a splendid day on Thursday, with sun, highs in the 80s, and not a rumor of a raindrop.
However more shower chances pop up Friday afternoon into the weekend.
The government’s Climate Prediction Center’s two week outlook through July 11 has odds favoring above-normal precipitation.
» READ MORE: The summer outlooks called for above-normal temperatures, but they haven't happened yet
It also favors above-normal temperatures, but no serious heat is expected in Philly for at least the next several days, and all that water to evaporate should divert some of the sun’s heating energy.