The Lehigh Valley is facing a “significant and likely record-breaking early-season heat event this weekend,” the National Weather Service warns, with temperatures in the 90s and a heat index approaching triple digits.
The heat and humidity expected Saturday and Sunday will bring the hottest conditions since last summer, and in some places record highs are expected.
In the Lehigh Valley, temperatures on Saturday could exceed the record high of 92 degrees set in 1934. The predicted high is 94 degrees, with a “lookalike” temperature around 98 degrees.
“Saturday continues to easily look like the hottest day in the streak,” the weather service wrote in its latest forecast discussion.
Meteorologists say large-scale subsidence (a downward movement of air in the atmosphere occurring over a fairly wide area) and forecast abundant sunshine made for a high-confidence forecast.
“A heat advisory will be required at least for the urban corridor and possibly other parts of the region,” wrote NWS meteorologist Jonathan O’Brien.
Heat advisories are issued within 12 hours of the onset of a forecast heat index of at least 105 degrees but below 115 degrees for less than 3 hours per day, or overnight lows above 80 degrees for 2 days consecutive.
Another warm day is expected on Sunday thanks to a slowing trend with the arrival of a cold front, the weather service said. Most areas will return to the 90s, and may even be close to the Urban Corridor Heat Advisory criteria again.
Heat is expected to subside as scattered to widespread thunderstorms develop ahead of a cold front expected by Sunday afternoon. Showers and thunderstorms will be possible from late Sunday afternoon until nightfall.
Behind the front, forecasters say we can expect much more seasonal temperatures to return to the region, with highs in the 70s expected Monday through Wednesday, lows in the 50s and lows in the 60s.