Over the years I’ve grown very averse to driving in wintry weather.
I try to avoid it at almost all costs because why would I introduce an unnecessary risk if I don’t have to? Friday morning is one of those times when I’d suggest staying home if you don’t have to go on the roads, in spite of the fact that they may be passable. Winter weather advisories are posted for much of the area tomorrow due to the freezing rain and sleet.
There’s a lot going on in the atmosphere over the next 24 hours, none of it really good. Our mild Thursday will slowly turn wet overnight with a period of steady rain developing. As the rain continues, colder air is going to be arriving. The rain will be heavy enough to create some urban street flooding before the cold air arrives.
Because cold air is heavy and dense it’s actually going to show up at the lowest levels of the atmosphere close to the ground before it shows up higher. The best way to show this is by looking at a predicted profile of what the air will look like tomorrow mid-morning. Notice below that at the surface, temperatures are forecast to be below freezing with a northerly wind but a couple of thousand feet above the ground it’s actually going to be warmer than freezing with a southwesterly breeze.
When temperatures above or warmer than they are below we call this an inversion and powerful inversions like this lead to sleet or freezing rain.
The structure of the atmosphere each hour tomorrow will be critical as to what type of precipitation we are observing. The more significant the warm layer is above, the better chance we’ll have for rain to freeze upon contact with the roads and trees and wires.
As the cold air starts to become more pronounced, the rain will have a chance to refreeze into sleet pellets. While not an ideal precipitation type it’s a lot easier to navigate and of course doesn’t cause as significant problems.
Total accumulation from the sleet and freezing rain will be a coating to an inch or so of slop with the more significant snow and sleet accumulation confined to northern New England.
The change from rain to freezing rain and eventually sleet will occur starting in Northern Massachusetts a couple of hours before sunrise, moving into Greater Boston around 8:00 a.m., and then progressing south from there.
At first the rain will freeze going from liquid to solid but eventually you’ll start to see sleet pellets mixed in. The faster the atmosphere cools down, the faster the sleet will develop and the less of a chance there will be for any significant problems from freezing rain. This is what most indicators are showing, however if the transition from freezing rain to sleet takes a little longer there will be more glaze on things like tree limbs, wires, and other surfaces.
Be sure you have a good ice scraper in your car tomorrow and put your wipers in the upright position if your car is sitting outside.
After starting in the teens on Saturday, temperatures will only reach around 20 degrees and then it’s very cold for Sunday morning with a few spots right around zero. The weekend will be dry with plenty of sunshine.