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Environment & Science

Lehigh Valley under heat advisory, with steamy conditions into next week

Max heat index
Mount Holly
This graphic from the National Weather Service shows the maximum heat index in the region on Friday.

BETHLEHEM, Pa. — The Lehigh Valley is looking at a heat index in the triple digits over the next few days as it heads into another heat wave, forecasters say.

A heat advisory is in effect is in effect until 8 p.m. Saturday, with "feels like" temperatures of 100 to 104 degrees across the region, the National Weather Service said.

The advisory covers Berks, Bucks, Chester, Lehigh, Northampton and Montgomery counties.

Warm and humid conditions will persist around the clock, forecasters say, with daytime temperatures in the 90s and overnight low temperatures in the 70s expected to stretch through Tuesday.

Second heat wave incoming

It will be the region's second heat wave of the year, coming behind a six-day stretch in June where temperatures reached or exceeded 90 degrees.

Four major climate sites had their hottest June on record, according to the Northeast Regional Climate Center, and others tied their all-time-warmest low temperatures on record during the mid-month heat wave.

The Lehigh Valley had several records of note, with a record high low temperature of 71 degrees on June 24, tying the previous highest minimum temperature set in 2017.

The temperature also soared to 96 degrees at Lehigh Valley International Airport both June 23-24, breaking the previous daily records of 95 degrees set in 1965.

Overall, with an average temperature of 72.7 degrees, it was the area’s sixth-warmest June ever.

Showers, storms expected; may be severe

Thursday's brief but heavy rains both delayed and cut short fireworks and other Fourth of July celebrations and brought a welcoming, albeit short-lived, cool-off.

The weather service said scattered thunderstorms are expected to develop again Friday, particularly north of the Philadelphia metro area.

Storms will be more widespread on Saturday and severe weather "can't be ruled out," the latest forecast discussion said.