A record-tying 90-degree high this week may foreshadow a toasty summer, forecasters say

The pulse of warmth this week, which evidently has set off a love fest for tree and grass pollens, may well end up having been spring training for the summer heat to come, according to forecasters.

Monday’s high of 90 degrees tied a record for the date, marking the first time in 15 years that Philly’s temperature hit 90 in April. Tuesday marked the third consecutive day of 80-plus readings at Philadelphia International Airport. In its updated monthly outlook posted Tuesday, the government’s Climate Prediction Center has odds favoring above-normal temperatures in May for the eastern half of the country.

Harbingers?

The sports-betting universe hasn’t yet penetrated the world of seasonal temperature guesses, but meteorologists in the early going are saying the smart money would be on a hotter-than-average summer, here and all over the country.

Nationally, “this could end up being one of the hottest summers on record,” the Weather Channel said in its pre-season outlook two weeks ago. AccuWeather Inc. on Wednesday called for temperatures to average two to four degrees above normal across the country, with Philly experiencing 36 to 42 days of 90-degree readings or higher, well above historical averages.

The climate center’s summer outlook favors warmer-than-normal temperatures throughout the contiguous 48 states, save for a patch of the far-northern Plains.

A thermal revolution is underway in the equatorial Pacific, where a once-potent El Niño’s warming of sea-surface temperatures is “rapidly fading,” the climate center says, with the cooling especially rapid in subsurface waters.

The ocean temperatures are forecast to slip below normal during the summer — perhaps as early as June — entering the state of La Niña in August. Weather moves west-to-east, so the changes will have significant impacts across North America, and are a big reason behind those forecasts for an active and destructive hurricane season.

Precisely what effects they will have on temperatures around here are unclear, but Todd Crawford, the meteorologist who worked up the Weather Channel outlook, says he expects La Niña to add of dash to steam to summer temperatures.

In addition to the equatorial Pacific, the climate center scientists rely on models and a variety of statistical analyses.

And once again, they are looking at the trends of recent summers.

The trend of warmer summers has been more than evident in the Philadelphia region, tracking with the planetary warming trend.

“We’ve had a lot of the warmest ones in the last decade or so,” said Ray Martin, a lead meteorologist at the National Weather Service’s Mount Holly Office.

In the 150 years of record-keeping, all of the 10 warmest summers on record have occurred since 1991. Six have occurred in this century, including the warmest, with an average temperature of 79.6 degrees, in 2010, and No. 2, 2022′s 79.3 degrees.

Fortunately, in recent years the region has evaded the long-lasting, killer heat waves that characterized the 1990s. But it has been consistently hot.

As for whether a 90-degree high in April says something about the coming summer, the short answer appears to be no, based on an Inquirer analysis.

Roughly once every decade, it has hit 90 in April, according to weather service records, although Monday’s reading was the first occurrence since 2009.

On average, the Aprils with a 90-degree day were followed by just over 20 days of 90-degree or higher readings — slightly below the long-term average. They ranged from as few as five in 1960, to 43 in 2002.

April warmth can be a source of torment for pollen sufferers, and the Asthma Center reported that tree and grass counts have been “extreme” for the last several days.

And April warmth evidently isn’t much help to the people who mud-wrestle with the atmosphere for a living. They readily acknowledge that seasonal forecasting is a work in progress.

The climate center had the odds strongly favoring above-normal temperatures last summer in Philadelphia, New Jersey, and Delaware.

But the average temperature for the June 1 to Aug. 31 period, 75.9 degrees, turned out to be shockingly normal.

Dean Iovino, a retired lead meteorologist and climate specialist at the weather service’s Mount Holly office, remarked at the time, “It’s very unusual for it to be that normal.”

But not that abnormal for a seasonal outlook to miss the mark.