A Philadelphia heat wave, the region’s first for 2025, hits this week.
An Environmental Protection Agency report found that heat waves nationwide are occurring more frequently, lasting longer, and are more intense, writes Garland Fordice for The Philadelphia Inquirer.
The article invites readers to choose a year to compare past temperatures with present temperatures.
Here’s how things have changed over 60 years, between 1965 and 2025.
Above 90 degrees (temperature)
In the late 1960s, Philadelphia saw an average of 14.6 days above 90 degrees per year. We now see an average of 30.4.
Heat index (temperature plus humidity)
In the late 1960s, there were, on average, 36.6 days when the heat index was above 90 degrees. We now see on average 49 days where the heat index is above 90 degrees.
Heat wave frequency
Local heat waves averaged 1.4 per year in the late 1960s.
Now, we have, on average, 4.4.
Heat wave duration
Philadelphia heat waves averaged 2.3 days long in the late 1960s.
Now, they last 4.6 days on average.
Heat wave season
Philadelphia heat wave season, on average, lasted for 11.6 days in the late 1960s.
Now, the heat wave season lasts 53 days on average.
Find out more and see how these statistics were compiled in The Philadelphia Inquirer.
Editor’s Note: This post was initially published on DELCO Today in June 2025.
