Will it snow in Boston this weekend?

A look at how a cold weather pattern may play out in the coming days.

Snow swirled in Boston last winter. –Craig F. Walker/Globe Staff/File

After a mild slug of air passes through on Tuesday and Wednesday, things are going to turn colder as we head into the weekend. As we head into the winter months, cold turns always bring with them the thought of snow. So let’s look at the chances of that over the next 10 days or so.

You may have noticed there have been some major fires across the West Coast. The warm and dry weather out West are connected to our upcoming cold.

Here’s why: The upper-level jet stream, which drives weather systems and air masses, takes on various configurations throughout the years. When the jet stream bulges further north, we call it a ridge, and when it dips further south, we call it a trough. Ridges and troughs meander across the country in somewhat regular fashion, but sometimes these patterns can become stuck for weeks at a time.

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During the upcoming 10-day period, it looks as though a trough will be stuck here in the eastern part of the United States, with that ridge persisting out west. This will keep average temperatures cold in New England but milder across the West Coast.

Troughs are conducive to storm development. The exact position of a trough, its depth, and its orientation all play a role in whether or not storms form. A shift of just 100 miles can mean the difference between a storm occurring over land or out over the ocean. These storms form as pieces of atmospheric energy at 18,000 feet or higher rotate around the flow.

via GIPHY

Credit: Tropical Tidbits

As we get into this weekend, several storm systems will be trying to develop along the boundary between cold and warm air on the right side of the trough. Forecasting exactly when the storms will form and just how close to the coast they will come is difficult within a couple of days of the storm, but even harder when we’re looking at five or seven days away.

There’s no doubt the temperatures are going to be slightly below average during the next 10 day. But how much precipitation we see in this time is questionable. Back in 1985, Boston was very cold during December but didn’t have much snow. This is because as storms moved into southern New England, the rain-snow line was far enough west of the coast that those areas were spared significant snowfall. I bring that year up because in some ways this December may end up mimicking that year as well.

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Another factor to consider is the dry weather we have had for the past six weeks. When we get into these dry patterns, and they continue through the first part of the winter, it can mean less-than-average precipitation, including lower snowfall totals.

Notice on the animation below there are areas of precipitation moving up along the coast later this weekend and into early next week. A shift of just 100 miles to the west means there would be some significant rain and/or snow for southern New England, but the storms could also stay offshore and keep us dry.

via GIPHY

Credit: Tropical Tidbits

Complicating matters is the fact that the models have not been consistent. At times a few days ago it looked like we might see some significant snow this weekend, but now it appears that may not come until sometime next week.

The bottom line? We are definitely going to turn colder and be on the edge for possible snow, but it’s just a bit too early to say definitively whether our world will be turning white anytime soon.

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It's snowing in parts of Maine
November 13, 2017 | 12:53 PM