Balmy weather has prevailed over much of the eastern United States during March, but the month’s final weekend promises a return of more wintry conditions. The lion and lamb seem to have traded places.
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Temperatures this weekend into early next week are to expected plummet 10 to 20 degrees below normal over much of the eastern third of the nation. Snow is expected in the higher mountains of the Mid-Atlantic and Northeast, as well as downwind of the Great Lakes. Along the Interstate 95 corridor, low temperatures will plunge below freezing.
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Milder weather will try to return by the middle of next week, but, on balance, chillier-than-average weather may hang around for the next seven to 10 days or so.
How cold and when?
Chilly air will begin spilling into the eastern United States on Friday, but the core of the cold arrives over the weekend and lasts through early next week. That’s when temperatures will generally be about 10 to 20 degrees below seasonal norms. In some areas on Monday, the departures from normal could be as much as 30 degrees.
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These departures translate to the following temperatures in these cities:
Chicago: Highs near 40 Saturday through Monday, with lows in the 20s. Cincinnati: Highs 40 to 45 Saturday through Monday, with lows in the 20s. Nashville: Highs in the mid-to-upper 50s Friday through Sunday, with lows in the 30s. Raleigh: Highs in the mid-to-upper 50s Saturday through Monday, with lows in the 30s. Washington: Highs near 55 on Saturday, 45 to 50 Sunday, and near 45 Monday. Lows near 30 Sunday and Monday (20s in suburbs). Buffalo: Highs near 35 Sunday and 25 to 30 on Monday. Lows near 20 Sunday through Tuesday. Some accumulating snow is possible Sunday. New York: Highs 45 to 50 Sunday and 35 to 40 on Monday. Lows 25 to 30 Monday and Tuesday. Boston: Highs near 50 Sunday, near 35 Monday and near 40 Tuesday. Lows in the 20s Monday and Tuesday.
These temperatures are much more typical of late February or early March, rather than late March.
On Sunday and Monday, the Upper Midwest, Great Lakes, Ohio Valley, most of the Mid-Atlantic and Northeast will all endure freezing early-morning temperatures. In Washington, these temperatures will probably end the peak bloom of the cherry blossoms.
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Gusty winds will intensify the cold. Forecast wind chills on Monday morning dip into the teens in the northern Mid-Atlantic and single digits in much of the interior Northeast. Subzero wind chills are even possible in the mountains.
Where snow is possible
A vigorous high-altitude disturbance will drop from the Upper Midwest on Friday into the northern Mid-Atlantic on Saturday. It will generate periods of snow in the central and northern Appalachian Mountains and also enhance lake-effect snow bands downwind of the Great Lakes on Friday night and Saturday.
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Even at lower elevations, ice pellets or graupel could mix with rain showers, including along the I-95 corridor from Washington to Boston on Saturday afternoon.
As a second disturbance passes through the Northeast on Sunday, more snow showers are possible downwind of the Great Lakes and on the westward facing slopes (upslope areas) of the Appalachians.
At least several inches of snow could fall downwind lakes Erie and Ontario, as well as in the high elevations of the Appalachians. Amounts will tend to increase with elevation.
The cause of the cold pattern
Weather systems are favorably configuring themselves for this wintry pattern. Significantly, a blocking zone of high pressure is setting up over Greenland. That’s forcing the jet stream, which divides cold air and warm air, to dive south over eastern North America. This is reflected by the negative phase of the North Atlantic Oscillation (NAO). When the NAO is negative, the weather over the eastern U.S. tends to be colder than normal.
Such a pattern was seldom seen during the core winter months, which resulted in generally above-normal temperatures.
Weather models show this negative NAO pattern persisting for a week to 10 days, although it will probably be strongest through early next week. As it weakens after that, forecast models simulate more variable temperatures in the eastern United States.
While the East shivers amid this pattern, the West will simmer. Temperatures are forecast to be 10 to 30 degrees above normal from the western Plains to the Pacific Coast Saturday through Monday.
Record highs in the 80s and 90s are forecast over interior California and southern Arizona on Friday. Over the weekend, record highs well into the 70s are predicted to spread through Nevada and southern Idaho on Saturday to parts of Wyoming and Colorado on Sunday, including Denver.