Storm HQ

We made it through November with just a few flakes, but your luck has run out. Mother Nature has decided to start December with a bang. We’ve got a very complicated storm coming, and for most of us, it’ll include snow, potentially a lot of it.

Today is a sunny albeit chilly day thanks to high pressure moving into southeastern Canada. As that high slides into Quebec, our sunny, chilly day will become a clear and cold night. Meanwhile the storm that’s been slamming the Rockies and Plains states for the past few days will head towards the Midwest. Normally, that would be good, as storms heading in that direction will move up the St. Lawrence Valley, keeping us mild with some rain. That’s not the case this time.

A secondary area of low pressure will develop off the Mid-Atlantic coastline on Sunday, and slowly drift south of Long Island. This will spread snow into the region during the mid/late afternoon hours on Sunday. Snow may fall moderate to heavy at times during the evening and into the first part of the overnight. As warmer air moves in aloft and at the surface, a change to sleet and then rain is expected along the coast, pushing inland as the night moves on. Precipitation should lighten up considerably toward daybreak as the low moves southeast of New England. So, that’s it, right? A quick 12-hour burst of snow and/or slop and we’re all done, right? Nope.

We’ll have some occasional flurries, drizzle, and freezing drizzle during the day on Monday as the system slowly moves out. At the same time, an upper-level low will move into the Northeast, spawning another system south of Long Island. This will bring colder air back into the region, with another period of steady snow Monday night into Tuesday morning, with everything winding towards daybreak Tuesday.

Now, there are several things that are still in doubt, that could have a significant impact on the forecast. First and foremost – the change to sleet and/or rain Sunday night. How quickly does the changeover happen and how far inland does it get? There’s at least one model that shows the change to sleet happening quickly and as far inland as southern New Hampshire, with a prolonged period of sleet for much of the evening and overnight. This is a detail that we’ll hopefully have a better handle on in the next 12-24 hours. Second problem – the second batch of snow Monday night. This is not set in stone either, and if it does occur, we’re still not sure exactly where that band sets up or how heavy it will be.

So, having said that, how much do we expect? Keep in mind, this is preliminary, and we will almost certainly update it again before the snow starts Sunday afternoon:

Cape Cod: 1″ or less, mainly with the batch Monday night:
Southeastern MA: 2-4″ (1-2″ Sunday afternoon, another 1-2″ Monday night)
I-95 corridor (Boston/Providence): 3-5″ (1-3″ Sunday afternoon/evening, 1-2″ Monday night)
North Shore/MetroWest: 4-7″ (3-5″ Sunday afternoon/night, 1-2″ Monday night)
Merrimack Valley: 6-10″ (4-8″ Sunday afternoon/night, 1-2″ Monday night)
Southern NH/NH Seacoast: 8-12″ (6-10″ Sunday afternoon/night, 1-2″ Monday night)
Central NH: 10-15″ (Mostly Sunday night into midday Monday)

Obviously, we’re staying very conservative with that 2nd batch, and we’re hoping to have better clarity on that with the next few model runs. We’ll update again tomorrow.