Just two weeks after all-time January record high temperatures, winter returned to Maine as wind chills dropped to below zero readings in the weekend leading up to Monday the 22nd.

There were indications that snow showers would occur during the afternoon but most of us were caught off guard by the magnitude of the event. Light snow started to fall around noon on Monday and continued through the day. All indications were that this event would be short lived, resulting in just a dusting of snow in Portland. The snow was extremely light and fluffy and thus piled up quickly. Snow finally tapered off in the early morning hours of Tuesday, but not before dumping close to half a foot of snow in the Portland area. The snow totals of 5 to 6 inches in Portland came on only .12" of liquid equivalent- or a snow ratio of almost 40 to 1! Typically here in Portland we are talking about ratios of 10 to 1. In the winter sleet storm the week prior, the ratios were close to just 2 to 1. The event was caused by another Norlun trough, a colloquial name for an inverted trough. In an inverted trough here in northern New England, the winds will be blowing from a generally easterly direction. A normal trough results in westerly winds here in Portland. The wind direction is of ultimate importance, because the east winds bring in moisture in from the Gulf of Maine; the magnitude of the event was exacerbated by the ocean water temperatures, which were close to 2 degrees above normal. The ocean surface is much smoother than the land across southern Maine. That means the wind slows down as it crosses from the ocean to the land. This creates a zone of convergence, resulting in rising motion of the air. The air coming off the Gulf of Maine is quite moist. So as the moist air rises, clouds and snow results. The trough did not really move very far over the day, so the accumulations were focused on a bulls eye around greater Portland. These events are very hard to predict, especially given the relatively sparse data in the Gulf of Maine- the Norlun trough is a surface feature and thus can really be only diagnosed by surface observations. the GoMOOS network helps, but much more density of observation is needed for us to properly prognosticate these events.