Another storm is on the way for tomorrow and I’m delighted to say it should put on a pretty good show with heavy snow and gusty winds. The leadup to this storm will be a bit unconventional as southwesterly flow around a low pressure system over Quebec brings milder air into the region. Normally we look to see high pressure over Quebec feeding cold air into the region ahead of a potential snowstorm but alas. Maybe next time.
This map shows several different analysis and observation products but most relevant for most of are the temperature observations which are all the little numbers. Note that our area is embedded within the warm sector of a low over Hudson Bay which means temps are generally in the upper 30s to mid 40s. A cold front is noted over the Great Lakes and behind it, temps are much cooler (10s/20s).
Today, we’ll be mostly feeling the warm air moving north ahead of the northern upper-level disturbance on the map above. Any time warm air is trying to root out some pre-existing cold air, we have to look out for clouds and some light precipitation.
That’s exactly what forecast model guidance is expecting across the area today, with the best shot of some light rain/snow up in the mountains. Showers could expand towards the coastline this evening but overall precip will be spotty and light today as high temps rise towards the mid 30s up north and mid 40s along the coast.
By tomorrow, the disturbances mentioned above will join forces off the Virginia Capes and we’ll have ourselves a rapidly intensifying storm headed northeast. The loop below shows a model forecast for energy around 20,000 feet aloft.
For those with a meteorological background, this loop contains a treasure trove of information about the storm’s forecast. But even if it just looks like pretty colors to you, hopefully you’ll find it a satisfying rendition to illustrate the merging of the disturbance over the Great Lakes with the disturbance over Missouri into a big storm approaching Cape Cod.
Precipitation will begin moving into the area tomorrow morning in the form of a cold rain. However, as the storm intensifies, it will draw cold air down into the region from Quebec. Additionally, we’ll get to enjoy a process known as “dynamic cooling” where furious upward motion and heavy precipitation northwest of the storm’s center drives a chain reaction of thermodynamic processes from the expansion of air parcels to the transfer of latent heat that allows the storm to manufacture its own cold air locally.
Thus by tomorrow afternoon, almost everyone except for the immediate coast south of Portland (east of the Turnpike) and Midcoast (south of Rt 1 especially) will be enjoying heavy snow with temps right around or just above freezing.
During the afternoon and evening, a process known as “frontogenesis” or the creation of a new frontal boundary will be helping to support very heavy precipitation. Where snow is falling, it will accumulate at a rate of 1-2″ per hour despite the relatively meager surface temperatures. Believe it or not, you can get rapid snowfall accumulations with surface temps above freezing! We last experienced this phenomenon on April 9th of this year when over a foot of snow fell across much of central Maine despite temps through most of the event sitting around 32-34F.
Because our storm will be driven by two disturbances joining forces, it will undergo bombogenesis which means its central pressure will drop by more than 24mb in 24 hours. What’s the upshot of that?
Not only will the snow fall heavily at times, but we’ll also have to deal with gusty winds. Winds will be sustained around 20-30 mph across the region tomorrow afternoon with gusts higher than that, especially along the midcoast. Normally this is a little below my threshold for talking power outages, but once you paste the trees and power infrastructure with heavy wet snow, it doesn’t take all that much wind to bring stuff to the ground. With that in mind, everyone should be ready for power outages tomorrow night that might drag on for a little while.
So how much snow do I expect? Here’s a look.
It’s always tough to tell where exactly the rain/snow line sets up and obviously that’s a pretty important part of the forecast. Right now, I’d draw it from the York County coast to Brunswick-Bath-Damariscotta-Belfast. Northwest of that line, snow totals will quickly ramp up to 8-12″ (or maybe a little more). But you won’t have to go very far southeast of that line to end up with bare ground. The big winner with this one will be the Sugarloaf area which could end up with as much as 18″. The snow up there won’t be the same cement that the coast will see but it won’t exactly be blower pow either. Honestly though, that’s good news. We want to build a dense base now so we’re not scraping rocks when the fluffier stuff hopefully shows up in January and February.
I’ll have an updated look at the storm forecast tomorrow morning.