With the air dense with water vapor and an energized atmosphere, the National Weather has posted a severe thunderstorm watch until 9 p.m. Friday for all of Bucks, Chester, and Montgomery Counties.
Wind gusts of 60 mph and pea-size hail were possible in the watch area, the weather service said.
Strong storms were pressing eastward late Friday afternoon, and heavy rains in western Chester County, the Lehigh Valley, and Berks County have touched off flood advisories. As the storms moved through Berks County, a gust of 65 mph was reported.
The fact that the sun came out for parts of the day and heating the surface might give the storms an additional kick.
The weather service said the level of potential storm energy was unusually high, as was the moisture potential.
The criteria for a severe storm includes wind gusts up to 60 mph.