Frost may become widespread concern as chilly air lingers

The month of May started off abnormally warm for cities from Chicago to Philadelphia, but AccuWeather meteorologists say the cool spell that erased that warmth could stick around for more than a few days.

After a stretch of mild conditions in the Northeast, temperatures quickly plummeted on Wednesday and Thursday, all due to a southward dip in the jet stream.

A high temperature of 72 on Tuesday in Pittsburgh was replaced with an afternoon temperature of just 58 on Wednesday. Similarly, Buffalo, New York, went from 68 on Tuesday to a chilly 52 on Wednesday. Cleveland experienced an even sharper temperature drop. Following a high of 72 on Tuesday, the temperature failed to get out of the 40s on Wednesday.

Temperatures settled in the mid-80s during the first two days of May in Chicago; however, the Windy City managed to reach only the mid-50s on May 6. A little farther north in Milwaukee, highs approached 90 on May 1, but by Thursday of this week, the high temperature managed to hit only the mid-50s.

This image, captured Saturday morning, May 8, 2021, shows freeze warnings (darker blue) and frost advisories (lighter blue) in effect during the early hours of the morning Saturday. (AccuWeather)

The chilliest day occurred on Friday in the Great Lakes with high temperatures as much as 5-15 degrees Fahrenheit below normal. Toronto, Ontario, reached a high of 50 F that day, the lowest high there so far this month, while the city usually sits in the lower 60s in early May. Temperatures began recovering in this area on Saturday, with highs in the upper 50s.

Some wet weather also accompanied the cooler conditions, helping to keep the temperatures low. On Friday, showers and thunderstorms stretched from the Great Lakes to the mid-Atlantic coast.

Low temperatures on Sunday morning resulted in the development of scattered frost in the traditional cold spots around the central Appalachians and eastern Great Lakes region, but temperatures did not dip this low over a vast area.

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Temperatures are forecast to stay below normal as the week begins.

Despite plenty of sunshine, high temperatures are forecast to reach only the middle to upper 50s through Tuesday in cities like Pittsburgh, Indianapolis and Chicago.

"The average high temperature for these three cities at this point in May usually hovers within one or two degrees of 70, so this extended stretch of chilly weather may come as quite a shock," Gilbert added.

With lighter winds forecast to accompany the lingering cold, frost may become a more widespread concern for interior portions of the Northeast.

"Overnight temperatures will be of concern for gardeners and fruit production interests across the mid-Atlantic Tuesday night, especially from western New York through far northwestern Virginia," said AccuWeather Senior Meteorologist Randy Adkins.

It is possible that some of the coldest locations could drop below freezing on Tuesday night, as Canadian high pressure settles into the region. However, this would likely be primarily in the Adirondacks of northern New York, where many trees have yet to bud. Farther south and east, the situation is different.

"With regard to fruit trees, many areas are a couple of weeks ahead of normal with regard to bud stages with some trees already post bloom," said Adkins.

He also explained that this makes the trees less tolerant to the cold.

"This raises the critical low-temperature threshold and narrows the range of temperatures between slight damage and significant damage with subsequent loss," said Adkins.

Since cold air is denser than warm air, some of the lower elevations actually tend to fall to a lower temperature than relatively higher elevations on a clear and calm night.

"Any warm-season plants that have been put into the ground will likely need to be covered, with potted plants likely needing to be brought in," Adkins said. "More cold-tolerant plants like kale, spinach or peas may be able to tolerate the cold shot."

Warmer air should begin to move into the Northeast by Wednesday. Although temperatures are still expected to be below normal for the middle of May, lows are expected to fall no lower than the upper 30s and lower 40s, which is high enough to prevent frost.

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