Norlun Trough Set To Bring More Snow Tomorrow Night

Hello everyone!

More snow is on the way! A clipper system will approach the region tonight before capturing and pulling a storm from the SE US up the coast in our direction. Precip will start tomorrow morning in the form of snow across the mountains. As the cold front associated with the clipper approaches, some of that snow may be squally in nature. Then, the real fun begins tomorrow mid day as a norlun trough sets up in SW Maine. Moisture will be funneled west along this trough and it will produce a band of very heavy snow. As the coastal low pressure system develops offshore, more bands of heavy snow could rotate into the region before the storm moves offshore Thursday morning.

18Z 3km NAM Showing Our System Getting Into Place Tomorrow Mid Day. Image Credit: Tropical Tidbits
18Z 3km NAM Showing Our System Getting Into Place Tomorrow Mid Day. Image Credit: Tropical Tidbits

Here’s a look at one model’s depiction of the weather map tomorrow afternoon at 1 PM. Note the Norlun trough developing along the New England coastline as moisture from the offshore storm is funneled back into the region. This process is a sure bet, where exactly it sets up and what the temperature is along the coast while it’s going on isn’t. Right now it looks like locations near Portland will start with a light rain/snow mix before going over to snow in the early evening. Exactly when this transition happens will be crucial in determining how much snow falls.

18Z NAM Showing Upper Level Dynamics Favorable For A Storm. Image Credit: Accuweather
18Z NAM Showing Upper Level Dynamics Favorable For A Storm. Image Credit: Accuweather

The Norlun trough will then become just another band on the west side of a coastal low due to upper level dynamics favorable for cyclogenesis offshore. A trough is diving SE out of the Great Lakes this evening and will ingest a disturbance currently moving through Oklahoma. The OK disturbance will tilt the trough negative tomorrow evening allowing for moisture to stream into the region. The upper level low will then close off to our south helping to keep precip going by wrapping in moisture and precip from the NE.

18Z NAM Showing Marginal Temps As Precip Arrives Tomorrow Afternoon. Image Credit: Weatherbell
18Z NAM Showing Marginal Temps As Precip Arrives Tomorrow Afternoon. Image Credit: Weatherbell

As precip gets going tomorrow afternoon, the biggest limiting factor will be surface temps. In the mountains, things will be plenty cold enough for a fluffy snow. More pow for the ski areas! Along the immediate coast, precip will start as rain. In between, a wet snow will fall. Exactly where the rain/snow line sets up and how fast it collapses SE will determine if the coast gets 6 or 16″ of snow. Any coastal rain will quickly turn to snow as cold air moves in later in the evening tomorrow.

Snowfall Forecast Through Thursday Afternoon
Snowfall Forecast Through Thursday Afternoon

Here’s what I’m thinking with regards to snowfall amounts. There will be a sharp gradient in NH as it’s a little uncertain how far west the heavier bands get. I’ll update this tomorrow when I know more. The snow in the mountains will be of the fluffy variety and of the wet/heavy along the coast. With all the recent snow, be mindful that loads on roofs will be getting very heavy so be sure to clear off as much as you can!

If you’re getting annoyed at this pattern, do know that a thaw is coming next week. If that thought makes you sad, winter will likely return to kick off March.

Wondering what a Norlun trough is? Check out my explainer in UpPortland from last winter.

-Jack

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