The winter storm that brought a coating of snow to downtown and a couple of inches to the northern and western suburbs is departing off the Northeast Seaboard early Sunday morning. At 3 a.m. the low center responsible for the storm was south of Nova Scotia while high pressure was over the lower Mississippi Valley. A large pressure difference between the low and high is sponsoring increasing northwest winds across the Northeast. These blustery winds will deliver seasonably cold air, which will be Sunday’s most salient aspect of the weather.
Northwest winds between 15 and 25 mph will be common, with gusts to around 40 mph. The day will begin partly cloudy, but skies should turn mainly sunny by midday. The aforementioned storm will reach the Canadian Martimes as high pressure reaches the Tennessee Valley, resulting in a marked slackening of the winds under mainly clear skies.
High pressure will depart the Southeast Seaboard on New Year’s Eve Day. This will allow winds to shift and blow from the southwest delivering milder by afternoon. A disturbance in the southern branch of the jet stream over the Southern Plains will summon moisture north from the Gulf. A vigorous flow aloft will allow this moisture to streak rapidly east causing clouds to increase along the Northeast Seaboard. Although the west winds in the lower atmosphere will dry, enough moisture may make it over the Appalachians to bring a fleeting rain or snow shower to the New Year’s Eve revelers.
The heart of this disturbance will cross the Middle Atlantic States on New Year’s Day, causing a several-hour period of light snow and rain somewhere between the city and central Virginia. At this point, it looks as though a vigorous northern branch of the jet stream will dip south from Eastern Canada, which will tend to suppress much of the moisture from this southern branch disturbance to the south of the area. That would keep the area mostly dry, with just a nuisance rain or snow show.