After a brief interlude of more spring-like weather with milder temperatures and some rain late last week and over the weekend, colder air is on the march southeastward from Canada and will become the dominant air mass over the Northeast until further notice.
In the wake of the cold front that moved through Friday night, the air wasn’t initially all that cold, and that was a blessing. Why? Well, several times this year we have seen mild, damp weather followed immediately by a direct discharge of pure arctic air, which turned surfaces shiny and firm … a gentler way of saying it became pure ice! This time, the incoming air mass was not cold enough to keep daytime temperatures below freezing, and surface conditions, while certainly more moist than the wonderful packed powder we have enjoyed much of February, were very carveable for the most part. Many states were wrapping up school vacations, while others were getting theirs underway, and from a business standpoint, the relatively mild temperatures were a very positive development for skiers, riders, and the resorts.
Now that cold air has returned, the surfaces have firmed up, to be sure, but over the next several days, there will be several ways for light snow to be generated over the Northeast and that will help morph the surfaces back to packed powder by later this week. As a new upper level trough develops over the region, the cold pool aloft associated with that trough will help trigger rather persistent mountain snow showers the next couple of days. Meanwhile, a series of fast moving upper level disturbances will race from west to east across the country in what has become a very fast moving split flow jet stream pattern. They will contain very limited moisture and thus have limited potential for producing significant snow, unless the northern and southern branches of the jet come together and phase. That combination of jet energy would help dig a deeper trough along the eastern seaboard, which would in turn help any surface low pressure center that forms to our south hug the coast to a greater degree, which would spread snow further inland. The first shot at such a system will come midweek, and right now, it looks as though the surface low will pass too far southeast of New England to be much of a storm for the resorts. That said, I think we will see a light to perhaps moderate snowfall develop because of a phenomenon known as a “Norlun” trough. The name Norlun comes from the two NOAA meteorologists (Steve NOguiera and WeiR LUNstedt) that did the research and identified the parameters necessary for one of these events. In short, a Norlun trough is an extension of a low pressure area that misses too far offshore.
The counter clockwise circulation around the ocean low helps pump moisture northwestward and onshore. If the air aloft from roughly 5,000 to 20,000 feet over the land is colder than normal, as it will be this week, it becomes unstable, which helps jack up the snowfall rate. The result is often a narrow band of snow that can become quite heavy for a period of time. The band tends to propagate from southwest to northeast as the low heads toward the Maritimes. The best conditions for a productive Norlun trough are found over Maine, as the surface low is generally stronger when it gets to that latitude, and it has had a longer time to generate the onshore fetch that moistens up the atmosphere. While this doesn’t look like an ideal set up, we should see light snow over much of New England and eastern New York on Wednesday, and that will help with the process of softening the surfaces.
The next shot at snow will come over the weekend, when a disturbance in the southern branch of the jet stream will approach the eastern seaboard and spawn a surface low in the waters down by North Carolina. There is a real question as to whether or not the system will be able to turn the corner sharply enough to impact the Northeast…right now I would lean against it. As was the case early in February when the polar vortex made an approach to the Great Lakes from the north, the cold air will tend to suppress the storm track, and my feeling is that while the Northeast will pick up fresh snow here and there in the next week, any heavier snow will be found in the central Appalachians and mid-Atlantic regions. Next week, when the PV will retreat somewhat to the north, I think we will have a better chance at seeing a substantial storm run the coast and bring us a late season powder day. Longer term, the signs are strong that another cold trough will develop over eastern North America about two weeks from now, which should keep the season chugging along by keeping temperatures cold enough to preserve snow and present us with more opportunities for sizable storms. March looks colder than normal to me, much like last March was, and there will be enhanced potential for snowfall over the next two to three weeks, so make your plans to make another trip or two to the slopes … spring is nowhere in sight!