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Fox News Weather Center

Mid-April Pattern Change May Yield Rain for California, Erase Persistent Chill in Northeast

A significant change in the weather pattern is anticipated for much of the United States during the middle of April.

The pattern change could bring some rain and cooler conditions to California and the Southwest, snow for the high country of the Sierra Nevada and Rockies and colder weather for Alaska, according to AccuWeather long-range meteorologists.

The pattern change could erase the persistent chill in the Northeast. The number of days with near- to above-average warmth could outnumber the chillier-than-average days in much of the mid-Atlantic, central Appalachians and the Ohio Valley.

According to AccuWeather Meteorologist Ben Noll, "If the pattern evolves as we suspect, it will also likely cause outbreaks of severe weather over the Central states as the storms move from the Rockies and onto the Great Plains."

Warm, moist air will flow northward from the Gulf of Mexico on a regular basis, which would fuel potential thunderstorms.

"There will still be some tendency for chilly air to occasionally dip into the upper reaches of the Northeast, from the eastern Great Lakes to northern New England and neighboring Canada, but these areas should get a break as well," Noll stated.

The setup could lead to late-season wet snow events in the upper reaches of the Northeast. While temperatures will trend upward in the region, it could be just cold enough at times for snow during a part of the storms that come calling.

"As we get farther along into April, the chances of a rapid meltdown increase following any big snowstorm, and there seems to be that risk in northern New England and upstate New York," Noll said.

Several indicators are suggesting that the jet stream will shift position from its persistent or re-occurring southward plunge in the East.

"A northward bulge in the jet stream is likely to develop in the East with a southward dip in the west about a week or so into April," Noll said.

The jet stream is a high-speed river of air high above the ground that separates cold air to the north from warm air to the south. This change in the jet stream position will set the pattern change into motion.

According to AccuWeather.com Meteorologist Mark Paquette, "We expect an area of high pressure over the western part of the Atlantic to get stronger and create a south to southwest flow of warm air in the East."

"Lengthening daylight will erode the cold air over central Canada, which has been a stubborn source region for the chill in the Northeast," Paquette said.

The longevity of the overall pattern, once it begins, is a question.

There is the possibility that after a week or two into the new pattern it could regress or flip back-and-forth between chill in the East versus the West.