After Potentially Record Warmth, Weekend Storm Could Bring Widespread Snowfall

BOSTON (CBS) – Gas up the snow blowers and dust off the shovels, winter is about to make an appearance.

Thus far, we have had very little impact from cold and snow. Sure, we have had a smattering of cold days and even some light snow accumulation here and there, but true New England-style winter has yet to rear its head.

Let me be clear, there are no blockbuster snowstorms in the forecast just yet, but a definite change to a more "typical" December weather pattern is on the way.

Before we get there though, we make one final run at 60 degrees and possibly a record high on Thursday. From coast to coast, the weather is highly volatile right now. A powerful storm is carving a path through the middle of the country and it will bring severe weather to areas where there is currently a solid snowpack (southern Minnesota), several inches of snow on the western side (Dakotas and northern Minnesota) and abundant wind and record warmth to a large part of the central and eventually eastern U.S.

Temperatures here in New England will top out in the low to mid 60s Thursday (the record in Boston currently sits at 64 degrees), and barely drop at all Thursday night. We will start in the 50s Friday morning and hover there until later in the afternoon when the colder air finally starts to pour in.

That brings us to this weekend. This isn't one of those will it hit or miss situations, a storm is coming. The difficultly lies with the marginal temperatures and who gets rain vs. who gets snow. The marginal temperatures aren't just at the ground level, but also aloft.

Many models are indicating a warm layer (above freezing) several hundred feet off the ground. And while it may seem rather innocuous, essentially the entire atmospheric column of air is cold enough for snow except this one tiny layer with temperatures barely above 32 degrees, that is really all you need to mess up a good snow forecast.

The precipitation comes out of the clouds as snow, falls for thousands of feet as snow, but then runs into a layer of air warm enough to melt the snow to rain…as it comes out of that layer and back into cold air, it would likely refreeze into sleet or freezing rain (once you lose the snow, there is no going back).

The forecast will come down to this layer of air, somewhere around 4,000-8,000 feet above our heads. If it warms above 32 degrees, you can just about kiss any meaningful snowfall goodbye. If it stays just below freezing, we have a widespread light to moderate snowfall accumulation, and you will be shoveling or plowing Sunday morning.

The worst-case snowfall scenario looks to be around 1-to-3" just outside Boston (north and west), a coating to an inch or so right at the coast and 3-to-6" north and west of 495 (north of the Mass Pike and certainly north of Route 2). Again, this is if and only if, the warm "nose" of air doesn't get involved.

If the warm layer materializes, we would likely get very little snow, perhaps scattered coatings to a few inches right off the bat (north and west) quickly transitioning to rain and sleet in all of southern New England.

Storm timeline:

First flakes and drops: late Saturday morning/midday

Peak: late Saturday afternoon through about midnight (worst travel)

Last flakes and drops: around dawn Sunday

Clearly there are some things to work out, typically as we get within 48 hours of a storm these small details tend to come into better focus. We will keep you updated with all the changes leading up to and during the event on WBZ-TV, CBSBoston.com and CBSN Boston.

Currently next week looks chilly and quiet with the general storm track moving well to the south of New England. So, this COULD be our last chance at a White Christmas.