BETHLEHEM, Pa. — Another day of sweltering temperatures will transition to a night of severe weather across the region, and concern has shifted to timing on when storms are expected to fire.
“Be prepared to have a way to receive warnings when you are asleep,” NWS Mount Holly said on X.
A radar simulation shared by the National Weather Service showed storms arriving in the Lehigh Valley area around and after 8 p.m. Wednesday, but some storms could arrive earlier.
Damaging winds appear to be the main concern, but large hail, heavy rain and tornadoes are possible, the weather service said.
Here is a radar simulation of generally when we can expect storms to fire up. The biggest impacts will be this evening and into the overnight. Be prepared to have a way to receive warnings when you are asleep. #NJwx #PAwx #DEwx #MDwx pic.twitter.com/BKG3wLL70x
— NWS Mount Holly (@NWS_MountHolly) June 26, 2024
The setup
The threat comes on the heels of hot, humid conditions smothering the region again Wednesday.
Temperatures pushed into the 90s in the Allentown area by early afternoon, and the combination of heat and humidity prompted a heat advisory in southeast Pennsylvania and parts of New Jersey and northern Delaware.
Heat index values up to 102 degrees were expected in those areas.
“There will be plenty of instability across the area,” the updated NWS forecast discussion said.
What’s to come
The Lehigh Valley remains in a slight risk for severe weather from the Storm Prediction Center, with damaging winds being called the main threat.
“There will be a chance for large hail, and an isolated tornado or two,” the SPC said.
Heavy rainfall also will be possible with any thunderstorms, with precipitable water values approaching 2 inches.
“They should be progressive enough to preclude a widespread flash flood threat," the weather service said. "Locally, though, there could be some flooding or flash flooding in and around urban and/or low-lying areas.”
Ahead of the main area of storms, some discrete cells may start to fire across eastern Pennsylvania and into New Jersey by the evening rush, forecasters said, though models continued to struggle and had noticeable differences regarding specific details of storms in the area around this time.
“Some of the guidance holds off most of the convection over our area until later in the evening when the main area comes through from the west," the weather service said.
"The upshot of all this is that some areas could see multiple rounds of storms during the 5 p.m.-to-midnight timeframe.”
Initial cells ahead of the main area of storms “could be discrete in nature,” but with potential for supercells or supercells within lines/clusters possible, sparking the concern for tornadic activity.
