Philly already set a temperature record Thursday. Expect another one later.

The Delaware and Schuylkill Rivers became swimming holes as kids sought relief from the record heat. Absent were the whirring and harrumphing of air conditioners, since almost no one had them in those days.

This hot spell bears some differences to that one in April 1941, including the fact that it is hotter.

Philly set a record even before the sun came up on Thursday. The overnight low, 65 degrees, was the highest minimum temperature for an April 16, three degrees above the 62 of 2002. Later that day, it reached 90, the standing record, and that one looks like it’s going to fall also.

Wednesday’s high at Philadelphia International Airport, 91, topped the old record for the date of 88, set 85 years ago.

The heat indexes are expected to remain below warning levels because the air will be bone dry Thursday, says the National Weather Service, which warned of an “elevated risk” of outdoor fire spread.

The sudden July incursion in the heart of the blossom season may present physical challenges to some people, “particularly to those of us in the Northeast,” said Richard Wender, chair of family medicine and community health at the University of Pennsylvania’s Perelman School of Medicine. “We kind of have an internal schedule that we live by.”

The trees, on the other hand, are proceeding with abandon in emitting their pollen. “This dry, warm, sunny, windy weather is exactly what the trees are going to appreciate,” said Manav F. Segal, allergist and immunologist with the Chestnut Hill Allergy & Asthma practice.

And exactly what tens of thousands of allergy sufferers don’t appreciate. Segal says he’s been getting ears-full from family members and friends, “and we’re not even at the peak of the season yet.”

Nor is this anywhere close to peak heat season. Wednesday and Thursday’s forecast highs, about 25 degrees above normal for the dates, would be above normal even in July and August.

It may be that a warming planet will make premature hot spells more common, but April has historically hosted its share of 90-degree days. The earliest official 90-degree reading in Philly occurred on April 7, 1929.

It has reached 90 at least once on 18 of the last 24 dates of the month, according to weather service records. On average, 90-degree readings have occurred in April every seven years. The most recent one was the 90 reached on April 30, 2024, the first since April 2009.

The all-time April high was 95 degrees, on April 16, 2002. Thursday’s high may flirt with that record.

April heat has a lot to do with the state of the trees, which are still being chary with shade. Former U.S. poet laureate Ada Simon has described the leaves this time of year as “patient, plodding, a green skin growing over whatever winter did to us.”

While allowing the sun to cook the ground, at this stage the leaves aren’t capable of holding as much moisture as they are during the summer. That helps limit the humidity since that means less evaporation, said Lee Robertson, a lead meteorologist with the National Weather Service Office in Mount Holly.

That’s one reason the weather service hasn’t issued any heat advisories. The heat indexes won’t be much different from the actual air temperatures.

“People still need to take precautions,” he said.

Gardeners and others engaged in outdoor activities should exercise prudence, Wender said. “You have to stop, you have to hydrate. ... There are times when you shouldn’t just push through.”

And Saval recommended wearing sunglasses. The pollen is likely to get worse before it gets better, he said, and the concentrations may be high enough to irritate even the eyes of those who don’t have allergies.

As sure as the trees are going to fill out, the heat is going to back off. Highs are expected to be closer to 80 during the weekend, and showers are possible Saturday night and Sunday. Of note, with its Thursday update, the interagency U.S. Drought Monitor has the entire region in “moderate drought.”

Behind the rain, temperatures are expected to be no higher than the 50s early next week. The normal highs are in the mid-60s.

It took a shade longer for the heat to back off in 1941. After setting what were then records on the 14th and 15th, temperatures crested at June and July levels for several days, not dropping off to below-normal levels until April 22.

The Inquirer front pages not surprisingly were dominated by World War II news, but the heat clearly was a local conversation topic. The Inquirer reported that “scores of boys took their first dips of the year in rivers and creeks.” The bodies of water mentioned included the Schuylkill and Delaware.

Encores are not expected this week, authorities indicated.