Warming trend triggers severe weather outbreak across Northeast

Sunshine and rising temperatures the past few days have given the Northeast a desperately needed reprieve from the chilly and dreary weather that pestered the region during much of April into May -- with some locations even getting the latest snowfall ever recorded. Even though the polar vortex will retreat and winterlike cold is not expected to return, unsettled weather will dampen the region and keep it cooler than normal much of next week.

The soggier stretch kicked off with a bang as severe thunderstorms threatened portions of the Northeast Friday afternoon and evening. On Friday afternoon, a tornado watch was issued across parts of five states as the atmosphere grew more volatile. For parts of central New Hampshire, the tornado watch was the first issued for the area in nearly five years.

On Friday evening, power outages in New York state peaked at over 66,000 customers out of power, according to poweroutage.us. National Grid had the vast majority of customers out of power in the state. The number of customers out of power in the state is decreased to around 40,000 as of early Saturday morning. The outages then tracked into Massachusetts, putting over 31,000 customers out of power.

The warmth and humidity helping to fuel these strong storms arrived just a day and half after widespread frost and even some freezes in parts of the interior Northeast, AccuWeather Senior Meteorologist Joe Lundberg noted.

Guests watch "Trolls World Tour," in the rain at the Four Brothers Drive In Theatre amid the coronavirus pandemic, Friday, May 15, 2020, in Amenia, N.Y. (AP Photo/John Minchillo)

“New York City and Philadelphia experienced their warmest days of the year so far on Friday. Philadelphia had its first 80-degree day of the year,” AccuWeather Senior Meteorologist Dave Dombek said.

“For New York City, Friday marks the second 80-degree day so far, after just nudging the 80-degree mark back on May 3,” Dombek added.

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On average, the first 80-degree reading in Philadelphia occurs on April 19. In New York City, the average first 80-degree day happens on April 26.

Forecasters say that Saturday will be one more gem of a spring day, as high pressure briefly slides across the Northeast, bringing sunshine and warmth along with it.

Temperatures will climb to near 80 in both New York City and Philadelphia. Widespread highs in the 60s and lower 70s are expected elsewhere in the Northeast.

"Anyone who wants to take full advantage of the weather and get outside amid the COVID-19 pandemic should do so on Saturday as a turn to a stretch of rainy and dreary weather is on the horizon," according to AccuWeather Senior Meteorologist Kristina Pydynowski.

Sunday will mark another shift in the pattern as an area of low pressure moves through the Great Lakes with its sights set on the Northeast and mid-Atlantic, where it will stall for much of next week.

"The wettest weather on Sunday will be around the Great Lakes," according to Pydynowski. "A couple of showers may also spread to the I-81 corridor, but most of the I-95 cities will be dry."

Drenching rain and thunderstorms from the Great Lakes will move into northern New England on Sunday night before sinking southward and stalling as an "upper-level" low pressure area.

"The upper-level low pressure area that develops early next week is not an uncommon feature in mid- to late spring," explained Lundberg.

"They form when disturbances ‘break off’ from the main flow higher up in the atmosphere. Around the periphery of these features, the weather is quite nice with sunshine and warmth. Underneath them, though, it can get quite cloudy, cool and wet."

Such will be the case where this feature stalls from southern New England into the mid-Atlantic and portions of the Carolinas and eastern Ohio Valley for much of next week.

Along the coast, onshore winds will be strong enough to cause coastal flooding around times of high tide. Early in the week, what is expected to become Arthur offshore of the Southeast coast could also add to the rough surf farther north along the mid-Atlantic coast.

"AccuWeather meteorologists are also closely watching the budding tropical system for where it tracks beyond Monday," according to Pydynowski. "The storm may head out to sea, but it is not out of the question that it or its moisture gets pulled into the mid-Atlantic or Northeast by this second storm. That would further enhance the risk of heavy rain and flash flooding."

Where clouds and rainy weather persist, temperatures by day will climb no higher than the 60s, with some of the coolest spots stuck in the upper 50s for a day or two, mainly across interior portions of New England, New York and northern Pennsylvania. The normal high temperature for this time in May in Boston is 67, and it's 68 in Burlington, Vermont, 72 in New York City and 71 in Scranton, Pennsylvania.

Temperatures so far in May have already been suppressed well below normal in these same locations, with the average temperature falling 6 degrees or more below normal in Burlington, New York City and Scranton and nearly 4 degrees below normal in Boston.

"A key difference to this pattern from the pattern we're just exiting is that nighttime lows will be much warmer," said Lundberg. "It's not an Arctic air mass but rather a large pocket of cool and moist air, so frosts and freezes will not be a returning concern."

Weather conditions are expected to improve toward Memorial Day weekend, when warmer air and sunshine are predicted to make a comeback in the Northeast and mid-Atlantic.

"Often called the 'unofficial start of summer', Memorial Day is expected to feel rather summerlike for most of the East," Lundberg said.

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