As if the pandemic were not enough, a blast of arctic air and snow is headed for the Northeast this weekend.
The cold snap will interrupt a spell of spring weather that had been something of a salve and had driven people out of their homes to golf courses and parks.
The National Weather Service has predicted that, beginning Friday night, the Arctic blast will move into the Northeastern states, bringing record cold temperatures. Parts of western Massachusetts could get up to two inches of snow, and temperatures in Boston are expected to plummet to 36 degrees with wind gusts of up to 25 miles an hour that will make it feel much colder.
In and around New York City, a damp Friday was predicted to descend into a rainy, blustery and maybe even snowy night, with temperatures falling below 40 degrees and wind gusts nearing 30 m.p.h.
The storm is the result of an unusually cold air mass from Eastern Canada that will travel southward into the Eastern states, bringing March-like temperatures from New England to as far south as Alabama and Mississippi, according to the National Weather Service.
“I would characterize the upcoming cold snap as highly unusual,” said Greg Carbin, chief of forecast operations at the Weather Prediction Center, part of the Weather Service. “We’re going to see a large number of record-low temperatures from the Gulf Coast to Maine.”
Mr. Carbin said that while daytime temperatures will most likely set records in many parts of the East, cloud cover will keep nighttime temperatures from being that extreme.
The weather will feel punishing after a mild winter and a spring so pleasant that it drew crowds to parks in New York City, raising concerns about social distancing. One silver lining of the frigid forecast is that it may keep people indoors as government officials continue to try to control the spread of the coronavirus.
In New York City, where temperatures soared to 80 degrees on Sunday, the temperature on Friday night is expected to drop from the high 50s to about 38 degrees. The Weather Service forecast wind gusts of up to 28 m.p.h., with rain likely and a “slight” chance of snow overnight in the region.
With the drop in temperature, advocates for homeless people feared that men and women kicked out of the subway during its overnight cleaning would be left to shiver in the cold if they refused to enter shelters, where the virus has spread. The Metropolitan Transportation Authority said that it would provide some buses for homeless people to stay in during the cold snap.
Should it snow, the Weather Service predicted only little accumulation: one to two inches in West Milford, less than an inch in White Plains and Paramus, and not even that in New York City.
On Saturday, temperatures during the day will warm up to only 50 degrees — 15 to 20 degrees below average for mid-May. It also predicted a 20 percent chance of showers in the afternoon, and even stronger winds, with gusts as high as 40 m.p.h. The air moving over New York City “was over the Arctic Ocean last week,” the service said.
Though those winds are expected to eventually clear the skies, temperatures will again sink to below 40 in New York, the service said.
The cold snap may feel shocking even to New Englanders, but snow in May is not unheard-of in that region. In May 1977, parts of Massachusetts received more than a foot of snow.
Cold air masses traveling south from Canada are common. But this late in the spring, more direct sun makes it less likely that the air will remain so cold. That is what makes this cold snap different, Mr. Carbin said.
“This time of year it’s really hard to sustain cold temperatures,” he said. “It would be very hard to get much more unusual.”
Mr. Carbin said the cold temperatures were a result of changes in the polar jet stream, the ribbon of high-altitude, fast-moving air that normally circles the globe over the Arctic. The jet stream has dipped to the south over the Midwest and Northeast. Such a dip is often called a blocking pattern, and when it brings cold Arctic air into more temperate areas, it is referred to as a polar vortex.
Mr. Carbin likened this jet stream pattern to a roller coaster, with the top over northwestern North America. As it moves to the southeast, the jet stream will pick up very cold air in the Arctic and in central Canada. “That air mass is what will be taking that roller coaster ride and down into the dip,” he said.
This jet stream pattern has persisted for most of the past month, he said, and has contributed to unseasonably warm temperatures in much of western North America. The upcoming cold snap is a result of the pattern becoming “amplified,” or more extreme, he said.
“It’s now jumped to where you’re bringing in the coldest air,” Mr. Carbin said. “And it’s doing it quickly.”
There is currently debate among scientists as to whether changes in the jet stream can be linked to climate change, specifically to the decline in sea ice in the Arctic Ocean that has contributed to rapid warming in that region.
Mr. Carbin said it was not unusual in spring months to see this kind of blocking pattern.
“It’s tough to pick out drivers for these weather regimes,” he said. “It’s possible that warming plays a role in favoring a more blocking pattern in the spring.”
Alan Yuhas and Nikita Stewart contributed reporting.