A wintry mix moving in could make roads slick on Thursday

The upcoming forecast overnight and into Thursday evening provides nearly every type of winter precipitation imaginable, from snow to sleet, rain to freezing rain — and even freezing drizzle. Where you are will determine what you experience over the next 36 hours.

Many of you will see nothing more than rain and, other than wet roads, really no impact. However, a large percentage of us will experience at least some frozen precipitation Wednesday evening. Roads could become icy as temperatures fall later Thursday.

Meteorologically, the setup is a warm front for the divide between cool and warm air pushing northward late Wednesday night. This contrast and temperature will create what we call lift, building clouds and precipitation.

I expect a mixed bag of everything to arrive this evening between roughly 5 p.m. and 9 p.m., from western areas to the North Shore. Because temperatures will be above freezing during this time, even if you see some sleet or snow, it shouldn’t accumulate on the roadways.

If you are in northern Massachusetts and up into Northern New England, there will be more snow and sleet. This is where somewhat significant accumulation is likely, and ski country should do fairly well out of this system. However, it will not be a blockbuster snowstorm.

One of the reasons for the mixed bag is a warm nose of air at higher levels of the atmosphere this evening.

The chart below is what we call a sounding. It’s a profile of the atmosphere from the ground all the way to the jet stream. The 32 degrees Fahrenheit line, which is important, runs at a 45-degree angle. In the graphic below, notice the area where the predicted temperature is to the right of this line, or above 32, is actually higher up in the atmosphere. This warm inversion will melt any snowflakes coming out of the clouds and that’s why we’re going to experience rain, freezing rain or even sleet.

Once a snowflake melts into a raindrop, it can never become snow again. But if it’s cold long enough, it turns into an ice ball known as sleet. If it’s just cold right at the ground and the liquid freezes on contact, that’s freezing rain. Because the structure of the atmosphere right above where you are is so critical in these situations, 10 or 15 miles can make the difference between what type of precipitation falls where you live.

I think most of the significant weather is over Thursday morning. However, during the day and especially in the afternoon, temperatures are going to slowly fall below freezing. There can still be some light drizzle or freezing rain. As this happens, any residual moisture will freeze and this can create a glaze of ice on the roads. I can see the potential for some sanding needs Thursday afternoon and evening.

On Friday morning, the sun is back out and we have Arctic air in place for a couple of days. Temperatures will actually be below average on Saturday, only reaching the 20s. There may be more storminess next week as March arrives.

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