Like just about everything — and everyone else — these days, the atmosphere continues to have an adversarial relationship with normality.

After a short-lived flirtation with May, a decided chill has resettled across the region, and frost could reappear on Mother’s Day weekend, when temperature readings might fall into the 30s.

“It’s a possibility,” said Dean Iovino, a lead meteorologist at the National Weather Service office in Mount Holly.

Visitors walk and ride on the Schuylkill River Trail on Sunday, when it actually felt like May.
YONG KIM / Staff Photographer
Visitors walk and ride on the Schuylkill River Trail on Sunday, when it actually felt like May.

Saturday likely will be among the chillier May days on record, with highs forecast just past 50. That’s about where they should be on Thanksgiving weekend; the record low maximum temperature for a May 9 is 49 degrees.

The atmosphere often is described as an “ocean of air,” and on Saturday afternoon it might sound like it, with 20-plus mph steady winds and near gale-force gusts, and the weather service says it likely will issue a wind advisory.

At a time when we should be talking about heat indices, wind-chills on Sunday morning will be near freezing.

Temperatures next week could average 12 or more degrees below normal, said Jack Boston, a meteorologist with AccuWeather Inc.

On Monday, when the “normal” high would be 72, readings might stay in the 40s, with a daylong cold rain if a storm develops as expected. “Monday might qualify as the most miserable day you could have in May,” he said.

In the meantime, the daytime highs this week, ranging from the mid-50s to mid-60s, will be 7 to 15 degrees below normal as “spring” continues to make a mockery of the long-term outlooks.

As an Arctic air mass spills southward, areas in northern Pennsylvania could see some wet snow on Friday, the day the state is due to lift some of the coronavirus-related restrictions in those regions.

Snowflake sightings are possible as far south as the Poconos early Saturday, the weather service says, and by Sunday morning temperatures are expected to fall into the mid-30s in Philadelphia.

May, we hardly knew ye

Despite temperatures well into the 70s during a spectacular weekend, readings since April 14 have averaged close to 5 degrees below normal, said Boston.

Since mid-April, a broad area of upper-level low pressure, a trough that favors cooler weather, has dominated the East. And this week and next, the region will be visited by an atmospheric celebrity, the polar vortex.

After spinning rather quietly in the high latitudes all winter, damming up cold air and depriving the East Coast of significant snows, the vortex has been dislodged, said Boston. It is being forced southward by strong air pressure systems over northwestern Canada and the North Atlantic that extend all the way to the Arctic.

The chill is forecast to persist and deepen by the middle of next week, with a few rough mornings for some of the region’s vulnerable plant life.

“There could be some problems with some of the stuff that’s already popped out of the ground,” Boston said.

When do we store the sweaters?

“We’ve got a pretty big pattern change coming,” said Boston, but “I wouldn’t look for any weather that’s going to require air-conditioning until the 20th of May.”

He said he sees a return to — dare we say, normality — by Memorial Day.

Then again, in both its mid-March outlook and March 31 update, forecasters at the government’s Climate Prediction Center said that the odds favored above-normal temperatures around here in April. The month finished 2.4 degrees below normal, despite quite a warm start.

As for AccuWeather, it called for April temperatures to be 3 or more degrees above normal.

The AccuWeather long-range forecast for April.
AccuWeather
The AccuWeather long-range forecast for April.

Much of the country ended up experiencing April temperatures below long-term averages.

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