Snow Saturday Evening, Ending As Rain Sunday Morning

21 below zero, that’s what the official temperature was in Norwood this morning. Many other areas were well below zero as well. This was the coldest morning for some places, but Boston stayed above zero, thanks to the heat island effect. This is when all the buildings give off some heat at night and keep the city much warmer than the surrounding countryside.

A new storm is moving quickly in our direction. This is not going to a major event, but will create more headaches. The themes for this system are: quick moving, not an excessive amount of precipitation, slick travel this evening into Sunday morning and most of the added roof weight, south of Boston.

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Across Cape Cod, where generally the precipitation will fall as rain, it will add weight to the snow. If you have less than 18 inches of snow on your roof and it’s structurally sound, I wouldn’t worry about it. Temperatures are going to be warm enough to melt some of the snow as well.

North of roughly the Cape Cod Canal there will be accumulating snow. I expect the further inland you live, you’ll have more snow. Those areas which stay all snow are still not looking at a big storm.

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Denser Snow
The snow will be heavier than past events, especially towards the end of the system. Most of what falls will be in the form of snow west of Route 128. Even if there is a period of rain, it’s not going to last very long.

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Some Freezing Rain
There’s an interesting principle of water known as supercooled water. Supercooled water is liquid, but the temperature of the water is under 32F. Typically, freezing rain occurs when supercooled water falls on an object and turns into ice. Late tonight and the first few hours of tomorrow we could still be seeing freezing rain even if the water isn’t super cooled and the actual air temperature is above 32F. This is because the roads, your car, trees and power lines are still very cold.

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In these set-ups there are often areas with just rain and other spots close-by with freezing rain. This is why both freezing rain and rain are in the forecast early Sunday.


Timing.
I expect snow to continue to become steadier and heavier this evening. The rain/freezing rain line then moves north and reaches south of Boston in the early morning hours of Sunday.

The map below is for 1AM Sunday morning. It’s about that time the snow will be getting wetter and could change to rain in Boston or points south. There’s a chance the snow never changes to rain in the city, the line will be that close.

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Between 6AM and 10AM Sunday morning, the bulk of the precipitation will be over, but a period of rain may linger over Cape Cod. Some sun could break through in the afternoon. It’s going to be a rather nice evening as well.

You’ll have a comparatively mild day to clear whatever falls tomorrow. For some of you the weight of the slush will be very heavy so take it easy. We haven’t had to clear much of the heavy stuff this winter.

Colder air returns Sunday night and most of next week. We could in fact see a few day that struggle to reach 20!

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The midweek storm is looking more like a non-event. Let’s hope this remains the case.

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