As Boston prepares for its first big winter storm of the season, temperatures were struggling toward 30 degrees Friday, in spite of brilliant sunshine. This cold air will be in place to provide the first significant snow of the season over the weekend.
The challenge to the forecast is going to be how much marine air comes in from the ocean during the first part of the storm. I'm confident that snow will be falling overnight Saturday, and into the first part of Sunday will be heavier and wetter. The rain-snow line placement will be critical to determine who receives the most amount of snow. Obviously, where it's raining the whole time, snow is not an issue; but where the transition occurs, amounts can ramp up very quickly.
MassDOT has advised the public to plan ahead if traveling this weekend, as snowfall will make driving challenging and lead to poor visibility. Construction on the MBTA's Green Line extension has been cancelled Sunday, meaning regular service will operate between North Station and Medford/Tufts. MBTA officials say regular weekend bus service will operate on Sunday, but if the forecast changes, some bus routes may operate on their snow routes.
"We did have a few spots of it last year, but bigger storm like this — it's been it's been a little bit of time," MassDOT Highway Administrator Jonathan Gulliver said at a press conference Friday. "So people aren't used to driving in this kind of weather. And we're asking them just really, really be careful. More so than usual, even."
Notice on my snow map below: I've highlighted a rough area of least confidence. This is because the rain-snow line will be fluctuating in this zone. The storm is just under two days away, and we'll get additional data Friday afternoon and Saturday morning, which will help refine the maps further. Suffice to say that Sunday looks like an unsettled morning with some improvement taking place in the afternoon.
Low pressure will traverse south of New England and then out to sea Sunday night. On this track, a rain-snow line will be present, eventually slipping south and east so that even portions of Cape Cod and the islands should see a few snow showers at the end of the system.
The heaviest snow will occur in the early morning hours of Sunday up through late morning. In the afternoon the snow will taper, but likely last in the air for much of the day. This second half of the storm will be giving us lighter, fluffier snow, which is able to pile up a little more.
The wind will be noticeable during Sunday — especially in the morning, blowing the snow and helping it to stick to the trees and wires. Where the snow is heaviest and wettest, there could be some scattered power outages. I suspect that as we get into the afternoon and it turns colder, the outages will decrease.
Because of all this, the National Weather Service has issued a winter storm watch. Some of these areas will convert over to warnings where it looks like six inches or more is likely; other areas will end up with a winter weather advisory where under six inches of snow are going to fall.
While we have this storm to contend with, there's another one on its heels for Tuesday night and Wednesday. This one looks significantly warmer, with another 1 to 2 inches of precipitation. This will exacerbate snowmelt and could cause some flooding. We'll have to take a look at this next week, but if you're susceptible to that type of flooding, it's a good idea to make sure your sump pumps are in working order this weekend.
In a press conference on Friday, Boston Mayor Michelle Wu said that based on the current forecast, she doesn't anticipate major problems with Monday morning's commute or any school delays or cancellations.
GBH News' Bob Seay and Matt Baskin contributed to this report.