The weather during the past month over the northeastern United States has been strongly influenced by two main atmospheric features: a “negative” North Atlantic Oscillation (NAO) and a “positive” Pacific North American Oscillation (PNA). These two features have had a significant impact on the upper-air flow pattern, and have generally allowed for average to slightly below-average temperatures over the Northeast, courtesy of periodic cold-air outbreaks from Canada.
However, the weather pattern over the past month has also generally been dry, with very little in the way of storminess. This has largely been a result of the structure of the jet stream. (The jet stream is an area of strong winds that are concentrated in a relatively narrow band in the upper levels of the atmosphere). There are two branches of the jet stream: the northern branch and the southern branch. When the two branches of the jet stream do not interact, the moisture-rich southern branch stays to the south, and we tend to have dry winter weather in the Northeast; however, when the two do interact (or “phase”) we are more likely to experience snow and Nor’easters in the Northeast.
While cold air has been in place with little interaction between the two branches of the jet stream, Williamstown has only seen two significant snow-producing storms so far this winter. The first snowfall, which brought 8 inches of wet snow between December 7 and 8, arrived courtesy of an area of low pressure that developed over the central part of the United States and tracked north and east. The second, more recent snowfall occurred almost exactly a month later. This snowfall, January 6-7, was brought to us by an early-season Nor’easter. A Nor’easter often begins as an area of storminess or energy (low-pressure) over the Gulf Coast states that treks north and east, eventually transferring its energy to a new area of low pressure that forms off the East Coast. However, the Nor’easter that took shape January 6-7 formed slightly further west, or inland, than usual. Therefore, the axis of precipitation also shifted west, shifting the area of heavy snow further west, into east-central New York, northwestern Pennsylvania and Western Massachusetts and allowing precipitation to fall only as rain over the big cities along the I-95 corridor.
Here in Williamstown, we had 13 inches of snowfall. Albany hit the regional snowfall-jackpot with over 17 inches. While these numbers sound high, this was not a particularly strong Nor’easter. The main limiting factor was the speed of the storm; with a very “progressive” flow aloft, the Nor’easter simply sped by. Had it slowed down somewhat, we might have seen widespread snowfalls of one to two feet or more. I won’t complain, though, since the 13 inches that fell were nearly perfect snow (very wet) for snowball fights and snowmen, and, of course, greatly aided the base of snow at local ski resorts.
While we have seen slightly below-average snowfall so far this winter, we are not too far behind, contrary to the grumbling of some snow-lovers at Williams. We have seen 22 inches of snowfall so far this season in Williamstown, while, on average, 27 inches of the white stuff has fallen by this time of the year. However, we look to continue close to normal temperatures over the meteorologically foreseeable future; thus, we still have plenty of time to reach our average seasonal snowfall of around 65 inches, but it’s going to take a couple of big storms to do that.