BOSTON (CBS) – You heard the phrase “anything but the sink”. That is exactly what we plan to do this week with the storm from Monday to Tuesday and the storm from Thursday to Friday. Snow, sleet, freezing rain, rain – you name it, it’s going to fall from the sky over southern New England this week.
So far this winter mainly the snow has turned. No real icing events that can often happen on a La Nina winter (like this one). Since I am referring to both freezing rain and sleet, I feel it is important to be able to distinguish between the two and understand exactly what they mean and why one is much more dangerous than the other.
CONNECTED: Some ice rinks in the Worcester area open for public skating with COVID logs
Think of the atmosphere above us as a cake. If snow is forecast, the cake on top is all below 32 degrees, easy. Things get a lot more complicated when the temperatures in the different layers vary as you climb.
Sleet occurs when you get a fairly large layer with temperatures above freezing. Normally, snow falls from the height of the atmosphere, melts into drops as it passes through the warmer layer and then freezes into small ice balls (sleet) when it falls back into a layer below freezing point. Sleet is nowhere near as dangerous as freezing rain as it usually doesn’t cling to surfaces, it just falls and collects in a layer of mini ice balls on the ground. You will hear the unmistakable “ping” of the side of the house and the car when the sleet falls.
Freezing rain is one of the most dangerous and dangerous types of precipitation. Freezing rain occurs when a large part of the atmospheric layer cake is above freezing point, but temperatures near the ground are below freezing point. So what you get is rain hitting the frozen ground, frozen cars, sidewalks, wires and freezing on contact. When it freezes a lot, it rains on these surfaces. You can measure this accretion with a ruler. Anything over 0.10-0.25 inches puts stress on limbs and lines and can lead to widespread power outages and tree damage. Some of the most devastating storms in our history are due to large amounts of freezing rain.
Ok, now that we’re all on the same page, what can we expect this week?
While we wait for the main storm to arrive, things will be easier on Monday during the day. Probably nothing will be noticed by the afternoon and even then the snow / mix will be light.
You only need to watch out for light icing in some areas until late afternoon and evening, but very little snow, perhaps a coating up to an inch north of the Mass Pike (Northern Mass. And Southern N.H.)
Our real storm comes after midnight. With milder air already present in some layers above the ground, very little snow will accumulate in southern New England.
The best chance for additional snow is in the far north of Massachusetts, western Massachusetts, and southern Vermont and New Hampshire. Even there, we’d only look at a few inches before switching to ice.
The hardest part of this forecast is determining where the sleet will fall compared to the freezing rain on Tuesday morning. At this point, I’d prefer sleet in areas east of Worcester County, including southern New Hampshire, because of the slightly colder layer cake on top.
CONNECTED: Mass. House Speaker: “Bring Teachers To The Top Of The Line” For COVID Vaccine
Further west and south, in places like Worcester County and Connecticut, freezing rain appears to be the dominant type of precipitation. As mentioned above, this increases concerns in these areas for ice build-up and tree / wire damage. We could see more than an inch of accretion in the Worcester hills and down through Connecticut.
A side note about freezing rain potential – usually our worst ice storms occur when we have a long duration of light to moderate freezing rain. In this situation, the event is of a relatively short duration with a higher intensity. If it gets too harsh, there can simply be a strong drain, making it harder to build up on surfaces (this would be a good thing). Something to consider.
Along the coast, east of I-95, it looks mostly like simple, cold rain. This includes the city of Boston, the immediate north coast through Cape Ann, and all of southeast MA.
REST OF TUESDAY
The icy mixture moves out quickly and switches off from west to east on Tuesday noon / early afternoon. Temperatures will peak in the early afternoon on Tuesday and will be above freezing to the north and west to around I-495.
However, in the late afternoon and evening, colder air enters and the entire area drops below freezing, freezing untreated or previously unfrozen surfaces.
Just after the mess on Tuesday morning, another major and messy storm comes towards the end of the week.
I won’t go into that much detail about this storm yet as it is still a few days away. But here are some points that are a little different from Tuesday.
- Seems to start everywhere as initial snow, the atmosphere is colder than on Tuesday
- A little early again for volumes, but think about something on the order of a 3-6 inch snowfall before we change the precipitation types
- The snow timing would be Thursday afternoon and evening
- Overnight we switch from south to north to sleet and freezing rain (icy mixture)
- By Friday morning enough warm air will likely have accumulated to turn ice into simple rain over the coastal plain and perhaps until after 495
- The remainder of Friday offers lighter and tapered rainfall showers. Temperatures could rise in southeast Massachusetts by the 1940s, reaching perhaps 50 degrees near or above Cape Cod.
None of these storms look like large wind producers. The Cape and Islands are at greatest risk of seeing gusts of 40 to 50 mph on both late Tuesday morning and Friday.
The tides are astronomically low this week, so expecting floods to hit the coast isn’t a big story either.
There is clearly a lot going on this week. We urge you to contact WBZ-TV, CBSBoston.com and CBSN Boston for regular updates on our weather team.
MORE: “You Can’t Hurry”: New Hampshire DOT shares Valentine’s road safety news
Follow Terry on Twitter @TerryWBZ