BETHLEHEM, Pa. — The National Weather Service now has placed much of the state, including the Lehigh Valley, under an extreme heat warning.
It’s the first issued since the NWS renamed its heat watch and warning products to improve messaging of hazards and provide better decision-making services.
The Lehigh Valley could now see its first 100-degree day since July 22, 2011, when the temperature soared to 104 degrees.
💯🌡️✍️ When was the last time it was 100°? Here is a summary of 100° day climatology for our 9 climate stations, including most recent 100° day, earliest and latest 100° day, normal and record high temperatures for June 23rd & 24th. #PAwx #NJwx #DEwx #MDwx pic.twitter.com/ky4N6XRwmM
— NWS Mount Holly (@NWS_MountHolly) June 20, 2025
First 90-degree day this year, first 100-degree day since 2011?
The warning is in effect from 8 a.m. Sunday through Wednesday evening next week, with dangerously hot conditions anticipated.
Heat index values up to 108 are expected, the weather service said.
The Lehigh Valley fell one degree shy of 90 on Thursday, meaning the upcoming heat wave also will bring the first official 90-degree day of the year.
Historically, the Lehigh Valley usually sees its first 90-degree day by May 24.
With the arrival of the summer solstice late Friday night, the summer benchmark now will fall inside of astronomical summer.
Temperatures are expected to soar into the 90s over the weekend, with these high temperatures expected in the coming days:
Saturday: 90 degrees
Sunday: 96 degrees
Monday: 99 degrees
Tuesday: 100 degrees
Wednesday: 96 degrees
Low temperatures will hover near 80 degrees in urban areas during this stretch, and in the low to mid 70s in the Lehigh Valley.
“Heat will have a cumulative effect on the body as the week goes on as little relief will come overnight,” the weather service said.
‘Widespread triple digit heat indices’
The weather service said the combination of air temperatures well into the 90s and dew points in the upper 60s to low 70s will result in widespread triple-digit heat indices.
"Sunday is the first really hot day, with highs expected to rise into the mid-upper 90s for most. Dew points will also creep up, passing 70 in some areas. This will bring heat indices up to around 100 or a little higher for most.
For simplicity`s sake, we`ve decided to upgrade the Extreme Heat Watch to a warning starting Sunday, even though it won`t quite reach warning criteria on Sunday," the forecast discussion said.
