After a beautiful day today, some big changes are on the way for Friday — especially Friday afternoon and then continuing into Saturday morning. Not only is the forecast messy with a combination of rain, sleet, and snow, but it’s also messy trying to pinpoint where most of that mixing happens. First we’ll give you the cliff notes of the Friday forecast and then we’ll get a little nerdy, because why not!?
You’ll probably wake up to a little sunshine tomorrow morning with clouds thickening through the morning before the ‘mess’ arrives Friday afternoon. Highs tomorrow will return to the 30s and back above freezing. That’s all part of the forecast challenge. When everything is said and done, the highest snow totals from Friday afternoon through Saturday morning will be where there’s very little contamination with sleet and most, if not all, of the precipitation falls as snow. That is northern Worcester county, the Merrimack Valley, and southern New Hampshire where we expect widespread 4-6″ of snow. Where some mixing happens, we’ll see 2-4″ which includes most towns down the pike from Worcester to Boston and down the South Shore** (note the asterisks there, we’ll come back to that). Along and south of Route 44, not only is the precipitation straight rain at times, you’ll have periods of sleet too, so not much accumulation down there.
Alright, let’s get a little nerdy and talk about some finer details. First let’s address the asterisks on those South Shore snow totals. Friday afternoon and evening, I’d expect a lot of sleet on the South Shore from Hingham down to Marshfield. When it’s mainly sleet you won’t accumulate much, if anything, especially with temperatures in the 30s. When you go to bed Friday night, don’t expect that snow to be on the ground there. In fact, for all of us, don’t expect the full amount to be on the ground when you go to bed Friday night. But for the South Shore specifically, at like 2 or 3 AM as the storm exits it will wrap in colder air behind it and change the precipitation over to snow for everyone, even down to Buzzards Bay and the Cape — hence your coating to inch possible. But for the South Shore specifically, when that happens you’ll get some ocean enhancement with a north wind. That enhancement will help give you a few inches of snow during the overnight and Saturday morning.
That’s actually a good note for everyone, actually. The timing of the snow starts Friday afternoon and initially it’s pretty light. With temperatures above freezing and lighter precipitation rates, there’s really not much accumulation before sunset. Then as the sun goes down and temperatures cool off, that’s when the accumulation starts or ramps up. I know we are billing this as a Friday storm, but the accumulation doesn’t finish until Saturday morning — and for some of us could be late Saturday morning (more on that later).
Before that changeover to all snow happens, there’s that period of sleet. In some cases there’s a clear signal that there won’t be much sleet — like our northern spots with the higher accumulations. And on the flip side, there’s areas where there’s no question about sleet and it’ll even rain (southern spots with lower numbers). But for some, like Boston, how much sleet is quite a big question mark. These are cross sections of the atmosphere Friday as seen from three different hi resolution models. We’ll continue discussing below the images, but as you scroll, see if you notice one big glaring difference between the three… “one of these things is not like the others“.
Ah, yes, not hard to miss. The third one has three glaring purple dots in the middle. What these images are is the temperature as you gain height in the atmosphere. Anything purple is above freezing. Now, at the ground, the precipitation can survive a tiny period of above freezing temperatures. I’m sure you can think of a few times where it’s been snowing at 34°. So it can snow, it’s just hard to stick. However, if the falling precipitation encounters above freezing temperatures on its way down, it’ll melt.
The difference between sleet and freezing rain, as you may know, freezing rain falls as rain and freezes on contact with the ground giving us black ice. Sleet is the actual ice balls that fall and the third cross section is a perfect example of sleet. As the snow falls, it melts in the warm bubbles, then re freezes as an ice ball as it exits that warm layer. Notice the other two don’t have that purple bubble. That means it’s snow all the way down to the ground. All snow means higher accumulations. All of this nerdiness to say there are still a few questions to be sorted out later tonight and tomorrow morning. I don’t expect DRASTIC changes, but the bands may wobble a bit depending on where we can or cannot pinpoint where it’s all snow and where there’s sleet.
Ok, that was fun, but enough rambling. Back to the forecast. The bulk of the storm will exit overnight Friday into Saturday but Saturday could have lingering on-and-off snow showers during the morning hours Saturday. For all of us, that may account for 1/2″ to 1″ of that total accumulation, or like the South Shore, a good chunk of it (previously discussed). The snow should taper off in the afternoon with a cloudy day Saturday. We’ll get a little sun and a tiny bump in temperatures Sunday before our next round of snow on Monday.
You may have heard grumblings about that Monday storm potential because it’s a coastal storm and those always have the potential to give us something big. Every time we deal with those coastal storms, you know that fine print we always give… IT DEPENDS ON THE EXACT TRACK OF THE STORM. This is no different, but we’re a little more confident in this track than some of the others we’ve had this winter. There’s pretty good agreement that the track will be far enough off shore to keep the sizeable and significant precipitation offshore. That said:
A) It still bears watching because it is close! And a little trend off to the north and this becomes something very different especially for the Cape and Islands.
B) That doesn’t mean we will have NO snow, it just means the big time stuff will be off shore.
I do think we’ll have snow showers around during the day on Monday. Those snow showers will be steadiest and heaviest the closer to the storm you are. Right now accumulations for most of us seem to be on the minor side, but a couple or few inches would be possible, maybe like a 1-3″ ballpark. The Cape and Island would have the potential of something like 3-6″, but that’s just eyeballing right now with the current track of the storm.
As we get closer to the storm, we’ll have those finer details and probably have an actual snow map this weekend, or perhaps even by tomorrow night. Stay tuned for that one!
