This evening not a lot has changed from my earlier thinking this morning. The timing of the storm is still such that the heaviest snow will fall later tomorrow morning and especially from about 3PM until 11PM.
The heaviest snow still will occur west of Route 128 and Route 495 especially in the Worcester hills. Here’s an updated map, but it’s very similar to what I drew this morning.
I have updated the snowfall map a bit, thinking the rain line may be a bit further west. Winter storm warnings are posted for areas in pink with the less severe winter weather advisories in blue closer to the coast.
The radar image below shows where the rain will be about 7AM tomorrow. If you are traveling tomorrow and you leave early you can avoid the worst of the storm.
EARLIER BLOG BELOW
A lot of clouds will be in the sky today, but it’s going to be mild. Highs will reach near or slightly above 60F. It’s hard to imagine many of us will be shoveling snow in 36 hours, but that is indeed the case.
A low pressure system is going to develop along the coast and move northward as a nor’easter. This storm will bring the typical weather associated with a storm on this track. Heavy snows inland, rain over Cape Cod, a mix in the middle, and high winds again mostly over Cape Cod and the Islands. The map below is a forecast for where the storm will be tomorrow evening.
The precipitation falls mostly from about 8AM Wednesday until about 1AM Thursday. The strongest wind will be later Wednesday and Wednesday night.
The image below shows projected radar around 1PM tomorrow. Notice the blue area, this is where it is forecast to be snowing. The exact position of the rain/snow line will likely fluctuate, but the further west of Route 128 you travel tomorrow, the higher the likelihood of snow.
The precipitation winds down very early Thursday morning. The next image shows the radar at around 1AM on Thursday, notice by then most of the precipitation has ended.
West of Route 495 snowfall will be heaviest. In these areas 6 to 10 inches of snow can be expected with more in isolated pockets. East of this region the snowfall will decrease until you get to the south coast where mostly rain will fall.
A closer look at the most populated areas.
The forecast is based on the predicted position of the boundary of something meteorologists call the coastal front. Below I have drawn where I expect the coastal front tomorrow evening at the height of the storm. If the front is 10 miles further west or east it will dramatically affect the amount of snow forecast.
To the east, the right side, of the front marine air will keep the precipitation mostly rain. These areas could see a bit of slush at the end of the storm, but it’s mostly a rain event. To the left of the front, we have a rain to mostly snow situation. The earlier the rain changes to snow, further west, the more snow you will have by the end of the storm. The models know about the coastal front, it’s just hard for them to pinpoint it. You can see how dramatically the snowfall numbers increase on either side of the front on the image below.
I have seen a 4 to 5 inch difference on either side of a coastal front. This means Logan Airport could see mostly rain or a slushy inch or two of snow while Brighton receives 3-5 inches of snow. It’s going to be a very close call.
I’ll be updating on Twitter and here as I receive new data.
Logan airport will likely only see delays. I don’t expect this is a situation where the airport closes. Flights in and out of Burlington, Vermont, Manchester and Portland, Maine will be impacted by the snow.
Amtrak trains run close to the coast and this storm, even if it was all snow, isn’t enough to halt operation on the rails.
Highways will be wet initially as the snow begins. As the snow comes down harder and harder secondary roads will become snow covered and then the highways. If you do need to travel tomorrow afternoon and you have choice which roads to take, try to stay closest to the coast.
The entire storm is over well before sunrise Thursday and that day is cold and a bit blustery with some sunshine breaking through the clouds.
When I make my snow predictions it’s for the grassy surfaces. What you end up shoveling might be quite different. The roads have quite a bit of heat built up from the past few days of warm weather. This means the first inch or two or even more could melt on the road before it accumulates. This means somewhat less to shovel.
The ground isn’t frozen and won’t be frozen when the snow begins. As the snow ends the snow will melt a bit from the bottom up. This is another factor is what you see on your lawn and the official total numbers.
Could We Get More?
I am quite confident with the snowfall prediction for areas west of Route 495 and areas south of Plymouth. In the metro-Boston area, if the coastal front were to move west past Route 128, this would be a rain event for many of you in that zone. If the coastal front stays off the coast, Boston and even Logan Airport would see 4-7 inches of snow. This is the part of the forecast that I will be refining later today and even early Wednesday morning.