By Terry Eliasen, Meteorologist, WBZ-TV Exec. Weather Producer


BOSTON (CBS) – It is the calm before the two storms! OK, so the first chance of snow isn’t a biggie, but the weekend is a whole different story.

So let’s break it down.

FRIDAY SNOW

Highs will struggle to get out of the 20’s Thursday setting the stage as a developing area of low pressure in the Midwest moves into New England overnight into Friday. This will be more of a nuisance snow than anything else. Light scattered snow showers will overspread the area between 2 and 5 a.m. Friday.

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Most of the precipitation will be light, but it may create some slippery spots on untreated surfaces. I expect a transition to rain along the coast and southeast through the morning. Showers wrap up and move out early afternoon. Overall, a coating to 1 inch is possible, possibly slightly higher across the Berkshires and higher terrain of southwest New Hampshire into northern Mass. What does fall, doesn’t last long as temperatures Friday afternoon will warm up to the upper 30’s to low 40’s.

WEEKEND STORM

Next up, a much bigger storm with bigger impacts this weekend, the greatest being snow and ice!

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It has been a while since our last significant winter storm. In fact it has been more than 300 days since our last big snowfall here in Boston! (March 13-14, 2018)

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As we start to go through the details, please keep in mind that we are days away from this storm and adjustments and shifts in track are possible that will directly impact timing and precipitation types and amounts. We typically like to be within about 48 hours of the first flakes before we start throwing numbers around. However, confidence is growing with regards to several aspects of the storm and some parts of New England will see more than a foot with this one!

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When Does It Start?

Expect the first flakes between 8 p.m. and midnight on Saturday. If you have plans to be out and about that evening, I wouldn’t be too concerned. It doesn’t look like one of those cases where it comes in like a wall of snow. In fact I wouldn’t expect anyone to top an inch on the ground until around or soon after midnight.

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After Midnight, The Party Starts Crankin’

Between midnight and dawn on Sunday, the snow really starts to pick up in intensity. And this is pretty much everywhere, all the way down to the south coast and Cape (perhaps with mixing over the Islands). This is what we call a “front end thump” of snow. It is during this time frame (from about 1 a.m. -7 a.m.) when just about everyone will pick up several inches of snow accumulation.

The Sunday Morning Mix

After dawn, warmer air will try to make a push northward. At ground level it will likely only be successful over southeast Massachusetts, and perhaps along the immediate coastline, changing many of those areas over to rain. Farther inland, say around the Mass Pike, it is very likely that the cold air will remain entrenched in place at the surface and the warmer air will be shoved up higher into the atmosphere. . . this will create a large area of sleet and or freezing rain.

Ice is never a good thing, as all it takes is a trace to create slippery conditions. When you start to get heavy ice accretion, it becomes a problem for power lines and branches. This type of set up will be very hazardous for travel on Sunday.

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Finally, somewhere north and west of Boston (exact location to be determined), the precipitation will simply stay all snow. Where this happens the snow amounts will be quite significant. There is certainly reason to believe that lots of folks in the all-snow area could receive one to two feet of snow!

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Flash Freeze To End

The precipitation will decrease in intensity Sunday afternoon and taper off completely Sunday night.

However, temperatures will drop rapidly below freezing Sunday evening.

Expect the rain to change back to a wintry mix, even snow on the tail end as the system pulls away. Any wet surfaces will freeze and bitter cold conditions settle in Sunday night into Monday. If you are traveling to watch the Patriots game, be aware of slippery conditions!

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Temperatures will tumble on Monday with highs stuck in the single digits in most spots with wind chills below zero.

Wind and Coastal Concerns

Given that there is a full moon this weekend, astronomical tides are running very high. The high tide of greatest concern will be on Sunday morning (occurring around 10 a.m. in Boston).

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The track of the storm will be critical with regards to the amount of coastal flooding on Sunday. A track a bit farther west means winds out of the south-southwest (an offshore direction, very little flooding).

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A track to the east and you have a more classic nor’easter- type event with strong onshore winds and a much greater risk of minor to moderate coastal flooding.

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Winds will likely be fairly light farther inland, any wind damage that occurs would be along the immediate coastline and particularly over Cape Cod and the Islands.

However, it won’t take much wind to take down heavy, wet snow covered branches and power lines inland, as well as those encased in ice.

There is still plenty of time for shifts and adjustments in tracks with this storm. The energy for the genesis of this storm will come ashore Thursday in the Pacific Northwest. At that time, we will get a much better sampling for models (more data) and likely be able to really hone in on the details of the weekend.

As always we urge that you stay tuned to CBSBoston.com and WBZ-TV for updates leading up to and during the storm this weekend.

Follow Terry on Twitter @TerryWBZ

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