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Forecast

Two storms this week will affect travel

A man waited for the bus in freezing rain in Kenmore Square in January.
A man waited for the bus in freezing rain in Kenmore Square in January.Stan Grossfeld/ Globe Staff

The weather around New England is often complicated and this week is no exception. After finally reaching above freezing temperatures for the first time in six days on Sunday, the region is still poised to see several more bouts of wintry weather this week.

There are a few slick spots Monday morning, but the bulk of our next storm does not arrive until late Monday night and during the day on Tuesday. Warm air is going to be streaming at high levels of the atmosphere over the cold air at the surface. This will produce a temperature profile from the ground up to where the clouds are that is more conducive to sleet or freezing rain rather than snow.

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Freezing rain and sleet are the dominant precipitation types in the forecast Monday night and Tuesday.
Freezing rain and sleet are the dominant precipitation types in the forecast Monday night and Tuesday.NOAA

The problem is that as the snowflakes in the clouds start falling, they’re going to melt on their way down, and then that melted snowflake — a raindrop — will freeze on contact.

The situation has prompted the National Weather Service to issue a winter weather advisory due to icy travel later Monday night and early Tuesday.

A winter weather advisory is posted for much of the area for Monday night and Tuesday.
A winter weather advisory is posted for much of the area for Monday night and Tuesday.NOAA

Even with a tiny amount of freezing rain, roads can become treacherous. Below are three maps that show the probability of seeing a tenth of an inch, a quarter of an inch, and half an inch of ice build-up respectively. Notice that the chances of even a small amount of ice are fairly high west of the coastline, but the chances of significant icing, which I put at half an inch, are much less.

This doesn’t mean the forecast can’t change from now until late Monday when this begins, but the risk of a big ice issue is decreasing, not increasing. One or two degrees makes an enormous difference in these situations.

Probability of freezing rain.
Probability of freezing rain.esri
Probability of freezing rain.
Probability of freezing rain.Esri

The heaviest precipitation will fall between 1 a.m. and about noon on Tuesday. The trend will be that warmer air takes over.

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What usually happens in these situations is that the colder air gets stuck in some of the valleys of northern Worcester County and on into southern New Hampshire. There could also be a pocket of more serious freezing rain in interior Connecticut as well.

A mixed bag of precipitation moves into the area late Monday night.
A mixed bag of precipitation moves into the area late Monday night.Tropical Tidbits

The storm, which will be mostly rain by then, will wind down Tuesday afternoon and night, and Wednesday looks like a good clean-up day for whatever does happen. Another system moves in for late Thursday and Friday with more snow sleet and freezing rain. This end of the week system also looks fairly significant and like it’s going to cause travel issues.

I’m also mindful that many people have appointments for their first or second vaccine shots, and weather like this is not going to help the situation. Hopefully, the long lead time on these two upcoming systems means that municipalities will be able to treat roads, but I suspect that some individuals are going to end up missing their appointments, and the vaccination centers should plan accordingly.