One week after a series of sudden storms led the city to declare a disaster emergency, nature may be running it back.
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High winds, heavy rain, flooding, and even the possibility of a tornado and “large hail” are forecast Saturday, the National Weather Service (NWS) said.
Several rounds of rain showers are likely starting around 10 a.m., said NWS meteorologist Nick Guzzo. Thunderstorms are expected to develop throughout the day and should peak during the afternoon and evening, with the potential for severe weather remaining through midnight.
“The leading threats are damaging winds, potential for tornadoes, flash flooding, and then there’s the large hail,” Guzzo said.
Hail may be half an inch in diameter, Guzzo said, enough to dent a car. Guzzo recommended people stay inside during a storm.
The tornado risk is between 5% and 9% for the affected region, comprising a large swathe of eastern Pennsylvania, Delaware, and New Jersey. That’s not “completely uncommon,” but is a higher percentage than the more frequent 2% to 4% risk factor, Guzzo said.
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“In addition, the risk of a strong (EF2) tornado is notably high,” the forecasting service stated online, using the Enhanced Fujita Scale, which ranks tornado intensity from 0 to 5 based on estimated wind speed and likely damage.
Wind from an EF2 tornado ranges from 113 to 157 miles per hour, NWS said. Such wind can tear roofs from houses and snap or uproot trees, NWS said. Last Saturday, both of those things happened as a result of four microburst storms.
Between two and three inches per hour of rainfall is expected, Guzzo said. That’s enough to cause flash floods in urban areas. River flooding is not forecast but is a possibility. NWS issued a flash flood watch in eastern Pennsylvania, New Jersey, and northern Delaware, along I-95 and to its northwest.
For anyone looking for silver linings to the storm clouds, Saturday’s weather is expected to blow away the wildfire smoke that has hung over the region for several days. Saturday morning, the city’s air sensors showed air quality indexes remained well above 100. That’s unhealthy for all people, but not as bad as it was Friday.
Philadelphia remains under a disaster emergency declaration as a result of last Saturday’s storms, which downed nearly 300 trees and led to widespread power outages. The city did not respond to a request for comment Saturday morning.