Just as the soils were beginning to take on that cracked and dried look and the vegetation was working up a thirst, the rains have returned to the Philly region, and showers and possible thunderstorms may bookend the week.
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Heavy rains were expected Sunday evening to end the first seven-day period without measurable rain in Philly in two months. More showers were likely Monday and later in the week, forecasters said.
They won’t approach the destructive deluges in the Midwest, said Brian Hurley, senior branch forecaster with the federal Weather Prediction Center, in College Park, Md.
The threat of flooding in the Philly region Sunday into Monday would be only “marginal,” said Sarah Johnson, warning coordination meteorologist with the National Weather Service office in Mount Holly.
And around here, despite the generous rains that have fallen upon the region since mid-June, additional rain wouldn’t be altogether unwelcome, said Hurley.
Precipitation in the last 60 days has been well above normal everywhere in the region save for Montgomery County, where they were just about normal, according to the weather service’s Middle Atlantic River Forecast Center, which uses a network of stations in the counties.
However, not so long ago, as we headed into June, Philadelphia had experienced 16 consecutive months of below-average precipitation totals.
And drier times may be coming, Hurley warned.
Drought conditions have eased, but not disappeared
New Jersey and Chester County remain under state-imposed drought warnings, with residents asked to go lighter on the water usage.
“We’ve been putting a dent in that drought,” said Hurley, but in the latest interagency U.S. Drought Monitor update, most of the region remains “abnormally dry,” with parts of Burlington, Bucks, and Montgomery Counties in “moderate drought.”
Thunderstorm activity has been well above normal this summer, with the weather service reporting 19 days officially with thunder detected at Philadelphia International Airport. The average for the entire June 1 to Aug. 31 period is about 15 days.
It’s also been quite warm. In 12 of the first 15 days of August, the temperature reached at least 90 at the airport, and this almost certainly is going to end up being one of the warmer summers on record.
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The warmth and the rains are related.
Philadelphia has spent a whole lot of time on the western edge of the so-called Bermuda high, centered over the North Atlantic. Winds circulate clockwise around thecenter of high pressure, and areas to the west of the center (where we are) experience winds from the south and southwest.
Being on the edge also places the region in spraying distance of shower activity as fronts and minor disturbances approach along the western flank of the ridge, with daytime heating adding a kick to the storms.
Thunderstorms may become scarcer come September
Those convective thunderstorms, which can wring out rain in waterfall-like downpours, in all likelihood will become less numerous as September approaches and the days shorten, Hurley said.
“It does get a little harder to pop convection when the sun doesn’t do its thing as much,” said Hurley.
“In September we tend to dry out until we get tropical connections,” he said.
This year, however, those tropical connections may be scarce, according to the National Oceanic and Atmospheric Administration and other forecast services.
What could become the most intense El Niño — the anomalous warming of vast expanses of the tropical Pacific Ocean — in records dating to 1950 is rapidly gaining steam.
During El Niño, the interaction of the ocean and the overlying air generates powerful upper-level winds from the west that can shear apart tropical storms in the Atlantic Basin before they mature.
No Atlantic hurricanes have developed yet this season. Meanwhile, Hurricane Lala in the Pacific has caused extensive damage in Hawaii. Typically, when the Pacific is quiet, the Atlantic is active, and vice versa.
Lala is the 12th named tropical storm — those with winds of at least 39 mph — to form in the Pacific. The average for the date is seven.
In the Philly region, historically tropical-storm remnants have been generous sources of rainfall.
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Sometimes, however, they have been overly generous. (See Ida, 2021.)