BETHLEHEM, Pa. — The Storm Prediction Center has upgraded the Lehigh Valley and much of the region to an enhanced risk (3 out of 5) of severe weather on Thursday.
The main risk remains damaging winds, according to the National Weather Service, but large hail also is possible.
"Moisture is a key ingredient for any severe thunderstorm development, and we'll certainly have that."EPAWA meteorologist Bobby Martrich
“The tornado risk is not zero either,” the weather service said in its latest forecast discussion, noting it should be a more active day for severe weather than Wednesday was.
“With high PWs [precipitable water values], there could be localized flooding as well, though storms should be moving along.”
Dangerous heat will continue today, with heat index values of 95-100 expected generally south of I-78. Scattered severe storms are expected this aft/eve, with damaging wind as the primary hazard. Low potential for hail and a tornado or two will also exist. #NJwx #PAwx #DEwx #MDwx pic.twitter.com/fN7Hlg1YgS
— NWS Mount Holly (@NWS_MountHolly) June 19, 2025
Forecasters say the main risks would be “any unlucky training and very heavy downpours in the urban core."
"We have a very soupy — and I do mean soupy — environment that we are going to be contending with," EPAWA meteorologist Bobby Martrich said in his Thursday video update.
"Moisture is a key ingredient for any severe thunderstorm development, and we'll certainly have that," he said.
Timing
With temperatures in the low 90s and heat indices spiking toward 100, showers and thunderstorms are expected in the area by early evening.
Martrich warned some areas "might get absolutely smacked by a nasty thunderstorm, and a couple towns over, you're like, 'It was just a whimper.' It's one of those days."
He said any strong storms could see frequent cloud-to-ground lightning, very heavy rain and localized flash flooding.
Storms are likely to dwindle and push offshore by mid-evening, the weather service said, with a cold front moving through the region overnight.
"For a while it will be very warm and humid, but toward dawn [Friday] the cooler, drier air will finally push across the region. Lows will return to the 60s, but not until after the frontal passage very late," the forecast discussion said.
Short reprieve from the heat, then...
Forecasters say the reprieve from the dangerous heat will begin to come an end on Sunday.
"The air mass in place will become increasingly moist, with dewpoints likely rising into the low 70s on Sunday and remaining that way through mid-week," the weather service said.
"With high pressure in place, increasing moisture and ample sunshine each day, it will be likely be quite hot.
"Monday and Tuesday look to be the hottest days, with temperatures likely to exceed 90 areawide. Many inland locations outside of the Poconos could potentially reach the upper 90s or near 100. Heat indices could exceed 100 for a large portion of the area."
