As with any storm, particularly in the winter, details become more clear as we approach the actual event.

The two things we are most confident in right now:

1. Ski Country

Pretty much any way you slice it, Northern New England does great with this storm. Most spots see a foot or more of snow.

2. Wintry Mix South

We have high confidence that Southern New England will flip from snow Saturday night and early Sunday, to a wintry mix of rain, snow, sleet and potentially freezing rain during the day Sunday.

What we don’t yet know: just how much, or just where, mixing occurs.

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Jeffrey McWhorter/AP

With that in mind, let’s dive into some of the factors that we are still sorting out, and will impact the final forecast.

1. Storm Track

It’s a simplified way of looking at it, but the final storm track really is key to what happens on Sunday.

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If the storm passes south of New England, more cold air will remain locked across the area. This would allow more snow, including around Boston.

By contrast, a storm that comes farther north, or through New England, would draw in slightly warmer air that would result in lower totals in Southern New England than we currently anticipate.

2. Sleet vs. Freezing Rain

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This, arguably, is one of the biggest questions to figure out. Who in Southern New England sees snow versus sleet versus freezing rain when we do flip to the "wintry mix."

Sleet, the small balls of ice, accumulates much more slowly than snow. And freezing rain doesn’t accumulate at all—it just coats everything in ice. So, nailing down what falls in any given spot is tremendously important.

If cold air remains locked at the surface, but a lot of warm air rushes in at higher levels of the atmosphere, we’ll see more freezing rain. This would cut down on the expected snow, but it would make travel even worse.

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If the cold air at the surface is a little more intense, and less warm air surges in aloft, we may end up seeing a good deal of sleet around Greater Boston. That would also cut down on totals to some extent and be a little less menacing than freezing rain on the roads.

The extent of the warming aloft comes back to the first point—the storm track. The farther north the storm comes, the more warm air comes along with it.

As I said before though—we are confident that we go over to a wintry mix, we just have to nail down what type of mix it is, and how far north it goes.

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All of these questions will become better answered as we get closer to Sunday.

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