BETHLEHEM, Pa. — There is good news and there is bad news when it comes to the Lehigh Valley’s extended forecast.
The boundary in place that has caused endless days of cooler temperatures and wet weather finally has lifted north and departed the region.
That’s the good news.
The bad news is the weather replacing it will bring severe storm risks, additional rain and “unabated warmth,” forecasters say.
Wednesday
Temperatures today, Wednesday, should warm rapidly into the 80s for most, according to the National Weather Service.
The NWS said southern areas (Philly metro and points below) should flirt with or slightly pass 90 degrees away from the coast.
“With plenty of humidity, heat indices will be notably above air temps,” the latest forecast discussion said.
The heat and humidity also will trigger a round of afternoon and early evening thunderstorms, which the weather service said “will be a good bet for most of the region.”
The Storm Prediction Center has maintained an outlook for a marginal (1 of 5) severe weather risk, with locally heavy rains possible given the ample moisture.
Thursday
12:56am CDT #SPC Day2 Outlook Slight Risk: from parts of New England into the Mid Atlantic and North Carolina https://t.co/Y1WiOd8m1i pic.twitter.com/HuY8nl28x6
— NWS Storm Prediction Center (@NWSSPC) June 18, 2025
The very warm and moist southwesterly flow of air will continue across the area, the weather service said.
“Underneath partly to mostly sunny skies, strong surface heating is anticipated, with temperatures generally climbing into the upper 80s to near 90 across eastern PA and northern NJ, and into the lower 90s near/southeast of the I-95 corridor,” the forecast discussion said.
“There could be some gusty, straight-line wind damage with some of these storms.”EPAWA meteorologist Bobby Martrich
Not only will heat indices also climb into the upper 90s southeast of the Lehigh Valley — triggering a heat advisory for the urban corridor — severe weather remains a concern Thursday afternoon and evening.
The SPC has the area at a slight risk of severe weather (2 of 5), with damaging winds the main concern.
“This is going to be more straight-line winds,” EPAWA meteorologist Bobby Martrich said in his latest video update. “There could be some gusty, straight-line wind damage with some of these storms.”
Similar to Wednesday, model soundings also are supportive of efficient rainfall production, the weather service said, with local urban flooding possible with any strong storms.
Suffocating air mass to follow
After a short break Friday, heat and humidity are expected to escalate over the weekend, bringing a suffocating air mass to the region.
“We’re going to start increasing the humidity again on Saturday, and it’s going to keep going up ridiculously high after that point,” Martrich said.
Beginning Sunday, the risk of heat-related impacts is forecast to reach major (level 3 out of 4) on the NWS HeatRisk chart.
The extreme category (4 out of 4), which may be reached in our area by Tuesday, is the highest of four levels, described as “rare and/or long-duration extreme heat” likely to affect health systems, heat-sensitive industries and infrastructure.
“The primary story in the extended period looks to be very warm temperatures during the late weekend and into early next week," the weather service said.
"For next Monday and Tuesday, highs for much of the region are forecast to be in the middle to high 90s with heat indices forecast to exceed 100."
