Chilly air, frosts ahead for Midwest and Northeast into early May

AccuWeather meteorologists say that a late-month cool spell could erase the waves of warmth that have washed over the Midwest and Northeast during much of April, and how long the chill could last.

So far in April, it has been especially warm for most communities across much of the Great Lakes and the Northeast.

In Harrisburg, Pennsylvania, the first 23 days of the month brought temperatures of 6.7 F degrees above the month's historical average and surpassed 80 degrees four times, which is a temperature more typical for early June. Albany, New York, was even warmer when compared the the historical average, with a 7.1 F-degree departure from the normal temperature.

Cities along the Interstate 95 corridor have also been extremely warm for those same days, including Philadelphia, New York City and Washington, D.C., which have all averaged 6.5 F or greater departures from historical average.

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Into early May, AccuWeather meteorologists say that an active pattern is expected to bring episodes of invading chilly air with frosts and freezes in the North Central states and the Northeast's interior.

"Two main features in the atmosphere will combine to bring calm winds, but also down chilly air from high up in the atmosphere. Together, this could be the prime conditions for frosts and freezes" said AccuWeather meteorologist La Troy Thornton.

At the start of Tuesday, a frost and/or freeze was ongoing across much of the Upper Midwest and the interior Northeast. Subfreezing temperatures extended as far south as western North Carolina, with temperatures in the 30s in eastern Tennessee and northern Georgia. While this chilly air isn't unheard of in April, it is a stark change from the prolonged warmth earlier this month.

Through midweek, overnight low temperatures could drop down to the freezing mark from Minneapolis to Columbus, Ohio. Some cities like Madison, Wisconsin, and Lansing, Michigan, are forecast to experience temperatures in the upper 20s F.

For parts of the Ohio and mid-Mississippi Valleys, the growing season has already begun, putting sensitive plants at risk this week.

Home and business owners in the Midwest and Northeast who may have already purchased annual flowers and vegetable plants may need to cover their investment or bring them indoors, forecasters warn.

Recent warmth has caused bud-break and leaf-out much earlier than usual, putting some tender vegetation, such as fruit trees, bushes and vines at risk for damage during multiple nights of frost.

Across the Northeast, the normally colder spots are the locations more likely to see any frost, especially those in the Appalachians. Closer to the coast, major metro areas are likely to stay in the middle to upper 30s most nights, with minimal frost risk.

Even still, the stark contrast from the mid-April temperatures will be quite noticeable along the Eastern Seaboard.

In Boston, temperatures since the start of the month have flipped 57 degrees Fahrenheit from as low as 31 on April 3, to as high as 88 on April 13. In New York City, temperatures have ranged from 37 on April 8, to 91 on April 14, for a 54-degree difference. Hartford, Connecticut, had temperatures soaring into the mid 90s less than two weeks ago. This week, the city will be lucky to reach 60 degrees each afternoon.

Unlike in previous shots of cool air in the last few weeks, this one is likely to keep temperatures below typical late-April levels through the month without much relief. In fact, even more cool air could move in later in the week.

"For interior parts of the Northeast, the coldest air may wait to arrive until next weekend," said AccuWeather meteorologist Brandon Buckingham, who warned there may be a storm that arrives at that time, bringing a reinforcing push of cold air.

"Daytime temperatures may be more like March while clouds may keep temperatures elevated within the reaches of the storm," AccuWeather Senior Meteorologist Alex Sosnowski said. "In the wake of that storm, where the sky clears and winds drop off, frosts and freezes may again occur next week."

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