‘Fingerprint of climate change’: April heat wave could break a record in Philadelphia

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It feels like summer in Philadelphia this week, even before the leaves have fully sprouted on trees.

Forecasted high temperatures of around 90 degrees Fahrenheit in Philadelphia could break a daily record on Wednesday set in 1941 and tie a record on Thursday set in 2002.

The balmy temperatures will be roughly 20 degrees above normal in Philadelphia for this time of year.

Unseasonably hot temperatures are sweeping through the Mid-Atlantic and southeastern U.S. this week, caused by a ridge of high pressure over the western Atlantic Ocean that’s bringing warm air up from the South, said Paul Fitzsimmons, lead meteorologist at the National Weather Service office in Mount Holly, New Jersey.

Climate analysts say these hot temperatures fit into a trend of warming spring weather.

“This heat snap we are going to have does have a fingerprint of climate change,” said Jen Brady, senior data analyst with the research nonprofit Climate Central.

Climate change makes this week’s high temperatures in Philadelphia twice as likely, according to the organization’s Climate Shift Index, which uses models to compare today’s world to a world without human-caused carbon pollution. In some parts of southern Delaware and South Jersey, this week’s high temperatures are three to five times more likely to occur due to climate change, the index found.

Since 1970, Philadelphia’s average spring temperatures have risen roughly 3 degrees, according to Climate Central. Over that time period, the city’s growing season, defined as the days between the last frost in the spring and first frost in the fall, has lengthened by about a month. Trees are blooming earlier, bringing the potential of earlier spring allergies.

March was the warmest on record for the U.S. In Philadelphia, the first leaf out of early-blooming plants occurred a couple days earlier than usual, according to the USA National Phenology Network, which predicts the start of spring using historical observations, temperature and weather events.

Forecasters from the National Weather Service predict much of the U.S. is likely to see a warmer-than-normal May through July, with a strong likelihood of El Niño developing later this year. El Niño could intensify extreme weather events and drive global temperatures next year to new record highs.

Philadelphia’s warm weather is expected to cool off Sunday or Monday, Fitzsimmons said.

“It’s going to be well above normal through the weekend before our temperature starts to get a little bit cooler next week,” he said.