Large Nor’easter Brings Snow Aplenty to the Northeast

The first large nor’easter of the season brought heavy rain and snowfall to the northeast U.S. to welcome in the first weekend of December.

Near the end of this past week, a strong polar jet stream merged with the seasonal subtropical jet stream to form a large superimposed upper level trough over the eastern half of the United States. As the trough became negatively tilted early Saturday, the 5^th, rapid cyclogenesis occurred along the Mid-Atlantic coast underneath the lee side of the trough. On Saturday, the cyclone “bombed” in as little as 8 hours. A cyclone “bombs” when its central pressure drops at least 24 millibars, or hectopascals, in 24 hours or less. This particular cyclone dropped 24 millibars, from 996mb to 982mb, between 9AM and 5PM EST.  The storm had eventually dropped to 976mb around 1:00AM EST. A cyclone that bombs is said to have undergone “bombgenesis” and is indicative of a rapidly intensifying storm.

The term nor’easter is derived from the strong northeasterly winds that come onshore as opposed to the storm’s geographical location. These northeasterly winds pull a great deal of moisture off the Atlantic Ocean and overland which is why nor’easters tend to be large rain and snow producers. This storm was no exception.

Seeing as though these northeasterly winds are most prominent near the northwestern quadrant of the storm, that is where we typically find the heaviest and most widespread precipitation. Heavy rainfall quickly transitioned into snowfall through Saturday morning with the heaviest of the snow falling on Maine, New Hampshire and eastern Massachusetts. Much of this area was blanketed with well over a foot of snowfall, although Vermont, Connecticut, and Rhode Island didn’t miss out either having received anywhere from a few inches to a half of a foot of snow. The highest recorded snowfall total in the region was 18.4 inches at the Mount Washington weather observatory in New Hampshire where 104 mph wind gusts were also reported. A close second with 18.0 inches was Carrabassett Valley, Maine.

As of Sunday evening, most of the precipitation had moved northeastward offshore or into southeastern Canada, though moderate snowfall is still occurring in parts of northeastern Maine. The storm is well into its occlusion process meaning it is weakening as the trough has moved well off to the east causing the storm to become “vertically stacked” and will practically collapse on itself over the next day or two. As of 5PM EST on Sunday, the storm’s central pressure is back up to 985mb and the storm will continue to weaken as it moves further over the Atlantic.