Waves of Cool Air to Erase Warmth in Midwest, Northeast

By By Alex Sosnowski, AccuWeather.com senior meteorologist.
April 20, 2015, 10:57:37 PM EDT

A weather pattern favoring waves of progressively cooler air will set up across much of the Midwest and Northeast this week and could continue into early May.

The cooler weather will arrive after a storm impacts the area then moves eastward. The same storm produced snow and high winds across parts of the West this past week.

The storm will send rounds of rain and chilly Atlantic Ocean air into the Northeast early this week, following the potential for severe storms in part of the Midwest and East.


According to AccuWeather.com Long Range Expert Paul Pastelok, a southward dip in the jet stream will develop and will be centered around the Great Lakes much of the time during the latter part of the month.

The jet stream is a fast river of air high above the ground, around the altitude where planes fly, that often marks the dividing line between chilly air to its north and warm air to its south.


"The pattern will deliver several days of cooler-than-normal air and unsettled weather from the Midwest to the East Coast to end the month," Pastelok said.

Temperatures can recover to near- or above-average levels in between each wave of cool air, especially over the Ohio Valley and the Interstate-95 corridor. These areas are likely to experience the most sunshine.

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The most pronounced cooling and the greatest number of cloudy days are likely from the Great Lakes to the central Appalachians, New England and neighboring Canada.

Temperatures during some of the chilliest days in the pattern could be in the upper 40s to lower 50s in the northern tier states to the central Appalachians. A handful of days can bring highs in the 50s as far south as the Ohio River and the mid-Atlantic coast.

According to AccuWeather.com Chief Meteorologist Elliot Abrams, "It's possible part of the Great Lakes region receives some wet snow during the middle of the week."

As the pattern continues to evolve, there could even be some some wet snowflakes in northern New England and as far south as the central Appalachians.

The details on the magnitude of the chill and timing of the most unsettled days will unfold during the pattern this week.

As cool as the air will be near the ground, the air aloft will be much colder. Cold air aloft that accompanies the pattern often generates a considerable amount of clouds and sometimes rounds of showers and thunderstorms with hail. This activity tends to be the most common during the afternoon hours and diminish during the evening.

"The pattern, which is likely to linger into the first part of May, could also bring a round or two of frost," Pastelok said.

How widespread the frost will be will depend on the extent of nighttime cloud cover.

Where skies are clear and winds are light at night, parts of the Midwest and Northeast could experience a frost. A frost is possible in a portion of the Midwest during the middle of this week. The risk could expand into part of the interior Northeast late in the month and into early May.

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