Philly broke a high temperature record Monday, but a showery holiday weekend is expected

The Philly region is well acquainted with sequences of days with highs in the 90s. Usually they are polite enough to wait until June and July.

The temperature reached 96 degrees, topping the 64-year-old record of 94. Another high-temperature record — 96 degrees, also set in 1962 — could fall Tuesday, Pennsylvania’s primary election day.

It also could challenge the all-time official high for any May day of 97. That was set in 1991 during what was the most intense May hot spell on record and foreshadowed one of Philly’s hottest summers on record.

In addition to a heat advisory, a code orange air quality alert was in effect through Tuesday for the region for ground-level ozone, a hazardous cocktail brewed by the sun in combination with auto emissions and other pollutants. People with respiratory and other conditions are advised to limit time outside.

And just in time for the Memorial Day weekend, a radical cool-down is due to start Thursday, with showers possible Friday and Saturday and temperatures several degrees below normal.

In the short term, readings are forecast to be 20 to 25 degrees above long-term averages through Wednesday.

“It won’t be a really long heat wave,“ said Bob Oravec, a lead meteorologist at the Weather Prediction Center in College Park, Md., but ”everyone will be complaining."

At least it won’t be followed by a freeze, and if you can’t wait for relief, you might consider Wyoming. It’s snowing out there.

One reason the temperatures are reaching record heights is related to the overall dryness as rain deficits continue to grow. The lack of moisture in the foliage allows the sun to go to town to bake the ground.

And with moisture wanting for evaporation, the air won’t be as sultry as it often is midsummer. Heat indexes won’t be much different from the air temperature, said Nick Guzzo, a meteorologist with the National Weather Service Office in Mount Holly.

That’s why the weather has issued a “heat advisory,” in effect through 8 p.m. Wednesday, as opposed to a warning.

Wednesday’s temperature outlook is a bit more problematic.

A cold front will be approaching the region and it could arrive early enough to set off thunderstorms during the afternoon that would shave some degrees off the thermometer.

For now, highs are expected to be in the mid-90s.

The planet continues to warm, and the “normal” temperatures for April and May have crept up in recent decades.

While 90-degree readings in April and May are hardly the norm around here, they are not all that unusual, said Oravec.

This hot spell is the result of classic summer pattern in which high pressure off the Atlantic coast is importing hot air from the south. Winds circulate clockwise around centers of high pressure, thus areas to the west of the center experience winds from warmer places.

As so often happens, said Oravec, what happens out West is the opposite of what is happening in the East. The planet has only so much hot and cold air to distribute.

It’s quite cold in the northern Plains, he noted, and parts of Wyoming are under a winter storm warning with temperatures about 30 degrees below long-term average.

None of that wintry weather is heading this way, but by Thursday daytime highs may be as much as 25 degrees lower than they were Monday through Wednesday.

And the weekend may get off to a wet start, with showers likely Friday and Saturday, with more showers possible Sunday and Monday. Highs should be in the 70s, and cooler at the Shore.

Jersey Shore veterans have seen this movie more than a few times.

Looking ahead, the government’s Climate Prediction Center has the chances favoring above-normal temperatures the rest of the month.

And Oravec sees a 100% chance that we haven’t seen the end of the 90s.

“We’re heading for summer,” he said, “so we’re going to have more and more heat.”

Only 33 days to the summer solstice.