Weather Pennsylvania: Lehigh Valley braces for intense summer heat
A heat wave is set to grip the Lehigh Valley starting this weekend, with the region expected to experience its first string of 90-degree days (above 32°C) of 2025, forecasters say. The National Weather Service has issued alerts for intense heat and dangerously high humidity, as heat index values could climb into the upper 90s (above 35°C) by early next week.
From rainy chill to intense heat
After days of cloudy skies, scattered showers, and below-average highs in the 60s (16–20°C) to start the week, a dramatic warm-up will take hold beginning Wednesday. Temperatures will rise into the mid-80s (around 29°C), with a powerful Bermuda high setting up offshore by Thursday, allowing warm and humid air to surge in from the southwest.
By Thursday and Friday, high temperatures in the Lehigh Valley are expected to reach the low 90s (around 33°C), signaling the arrival of the first significant summer heat surge.
Risk of widespread heat-related impacts
The NOAA HeatRisk map places much of Eastern Pennsylvania — including the Lehigh Valley and Philadelphia metro area — under level 2 to level 3 heat risk, meaning most individuals, especially those without proper cooling or hydration, could be affected. Dew points climbing into the low 70s (21–22°C) will contribute to heat index values topping out in the mid to upper 90s (35–37°C).
Severe storms possible Thursday night before heat wave locks in
A strong cold front is forecast to sweep across the region Thursday evening, potentially triggering severe thunderstorms. The Storm Prediction Center has issued a 15% risk area for damaging wind gusts across parts of the Northeast and Mid-Atlantic.
Behind the front, a strong upper ridge is expected to dominate, ushering in what may be the first official heat wave of the season — defined as three or more consecutive days of 90°F (32°C) or higher.
Meteorologist Bobby Martrich expects the heat wave to peak Sunday
According to EPAWA meteorologist Bobby Martrich, Sunday, June 22, will likely mark the start of a short but intense heat wave, with temperatures reaching the low to mid-90s (33–35°C) through at least Tuesday, possibly extending into Wednesday.
“It’s going to be very soupy,” Martrich noted in his latest video forecast. “We’ll have a southwesterly flow, which brings high humidity and oppressive heat.”
The heat wave is expected to ease by Wednesday, June 25, as another front moves in. Martrich emphasized, “This isn’t going to be a weeks-long event — we’re looking at a 3-to-4-day window of serious heat.”
