More than 30 million Americans face severe weather risks at week's end

The warm and humid conditions in the Northeast could end with a bang as thunderstorms are forecast to erupt and could trigger severe weather into Friday night ahead of dramatically cooler air. More than 30 million people lie in the zone predicted to experience severe thunderstorms at late week.

A mass of clouds with embedded showers and thunderstorms spread over much of the eastern half of the United States on Friday, May 29, 2020. Meanwhile, a lack of clouds west of Lake Michigan and northern Illinois marks the leading edge of cooler and drier air. (NOAA / GOES-East)

The warmth this week pushed temperatures in dozens of locations to smash daily record highs, as some cities recorded their highest readings ever for the month of May. Burlington, Vermont, reached 95 F on Wednesday, which set not only a record for the date but also an all-time May record. Montreal and Quebec City also set all-time May records. Scranton, Pennsylvania, tied its all-time May record of 93 on Tuesday.

Temperatures in some coastal areas have been suppressed by cool ocean air, as some places became socked in by low clouds and fog. New York City has yet to reach 80 this week due to the cooling influence of Atlantic waters and fog.

Friday marked the beginning of the end of the weather pattern more typical of late June and July, but the warm and muggy conditions will set the stage for volatile weather.

A cold front that was over the Midwest during Friday afternoon will gather momentum and strength as it pushes toward the Appalachians during Friday night, then swings offshore this weekend. The front will act as a trigger for some big thunderstorms.

A tropical air mass has enveloped the Northeast in the wake of Bertha, which made landfall along the South Carolina coast on Wednesday as a tropical storm. Bertha weakened to a tropical rainstorm as it moved over land Wednesday into Thursday. The system has diminished over southeastern Canada.

As the cooler and less humid air from the North Central states moves in, it will cause the warm and humid air to be lifted. As that tropical air cools, it will form towering clouds, showers and thunderstorms.

The greatest threat for well-organized severe thunderstorms is forecast to extend from central West Virginia and northwestern Virginia, northward to central and and northern New York state, as well as southeastern Ontario and southwestern Quebec.

There will be a couple of downpours ahead of the main severe weather zone. Pop-up showers and thunderstorms are also possible east of the main severe weather threat zone, including across portions of the Interstate-95 corridor of the mid-Atlantic and New England.

"The storms are likely to be at their peak intensity until around 9 or 10 p.m. on Friday," Bill Deger, AccuWeather forecaster, said.

Still some communities can be slammed by a weakening storm later in the evening and during the overnight hours.

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There can also be some small hail with a few of the more intense storms.

"Locally damaging straight-line winds will be the primary threat from these storms," AccuWeather Senior Meteorologist Brett Anderson said.

An AccuWeather Local StormMax™ of 70 mph is forecast for wind gusts in the strongest storms. Winds this strong can knock over trees, trigger power outages and cause property damage.

"There will also be brief torrential downpours, but the threat of significant flash flooding will be reduced due to the steady movement of the storms," Anderson added.

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