Like a bad reality TV show, winter’s last stand looks to have several unwanted episodes as we head into early April. Having already seen our first event out of this newly active pattern, our attention now turns to the next two threats for winter weather which are on the horizon in the coming week.
Our first shot at winter weather arrives tonight in the form of a weak burst of warm air aloft which will set off some light snow in the mountains. This activity will also be associated with the push south of cold air at the surface in the form of a backdoor cold front. The combo of surface cold front and mid level warm front will lead to light snow in the overnight hours across the north country. Mainly snow is expected with light accumulations.
This light snow will provide the first ingredient for late week trouble: cold air. A sprawling Canadian high pressure system will build south behind this backdoor cold front delivering more cold air. This won’t be Arctic air but it will be cold enough to make precip that falls when low pressure approaches from the west fall in the form of snow/sleet/freezing rain for many as opposed to rain. Guidance is still struggling to figure out how long the cold will last but seeing as this is looking like a nearly classic Cold Air Damming (CAD) situation, I think it best to go with the old rule of thumb: CAD will always last longer than you think, even if you think it will last longer than you think. The long and the short of it is, cold air in Maine leaves when it’s good and ready, not when warm air tells it to and it’s about as motivated as a teenage boy.
Here’s the setup late Thursday evening as low pressure approaches from the west. Cold, dry air will be in place shown by isobars bending over our area and shades of Grey appearing in the Precipitable Water (PWAT) fields. The scale on the right shows how grey colors represent low PWATs and thus dry air. The image also shows sea level pressure which shows high pressure anchored to our NE feeding cold air south. The wavy nature of the warm front also signals the lack of a concentrated push north of warm air as well as the potential for redevelopment of low pressure offshore. The secondary coastal storm is something that guidance is hinting at and with the strong high pressure trying to ‘split’ the storm in two, this seems like a reasonable possibility. This is unlikely to lead to a strong coastal storm and precip is likely to remain light to moderate through the duration but it would help to keep that cold air locked in across the area.
In terms of impacts, this one will be a mix of snow, sleet, and freezing rain for most of the area with the far north possibly holding on to mostly snow and the coast seeing a change to rain at some point. Everyone will see slick travel Friday during the morning commute and roads are likely to remain slick for the evening commute away from the coast. While it is still a little early to call exact amounts, I expect a widespread 1-3″ of snow with coatings along the coast and 4 or 5″ possible in northern Franklin and Somerset counties. In terms of ice accretion, light to moderate amounts are likely and in some areas, especially inland, it could be enough to threaten power lines. This does not however look to be a major ice event. With the storm weakening and possibly splitting, there does not look to be enough precip to cause major issues.
I’ll have more info in the coming days on the Friday event.
Another round of wintry weather is possible early next week. While it is still a week away, there are reasonably strong signals we see some sort of precip. As always this far out, any and all solutions are on the table from snowstorm to rain storm to sunny day. More on that as we get closer.