Driving school

Freezing rain and sleet make driving dangerous Friday – CBS Boston

BOSTON (CBS) — Ice cream is no fun.

I would take snow any day on what happened Friday morning. As the temperatures dropped and dipped below 32 degrees, reports of accidents increased more and more. Roads that were once just wet turned treacherous in minutes. Sidewalks, driveways, steps, all untreated surfaces transformed into skating rinks. If it hasn’t happened to you yet, it is coming.

The cold air does not just spread the area in a straight line from north to south. When it first arrives, the cold layer is shallow (cold air is dense and sinks), so it literally seeps into the mountains and hillsides and first fills the valleys. The first hours are always the most dangerous. It still seems to be raining, but the water freezes on contact with the now cold surface (roads, driveways, etc.). With the rain continuing, it is impossible to pre-treat the roads. It therefore becomes a race against time for the teams to sand and salt the freshly formed ice.

As more and more cold air infiltrates our region, the cold air layer eventually becomes thicker and higher. Thus, the raindrops fall at sub-freezing temperatures for a longer period of time. This causes the formation of ice pellets called sleet. And that’s what we see today. A brief period of dangerous freezing rain followed by a change from that sleet to sizzling. Sleet will build up a little but will NOT build up on surfaces like freezing rain.

As the cold air continues to fill in, the entire “column” of air will eventually be cold enough to contain snow. This can happen quickly enough (before the precipitation stops) north of Boston to produce snow showers and patchy coatings Friday afternoon and evening.

AND AFTER?

Almost all areas north of the Massachusetts Turnpike are below freezing at noon, and by 4 p.m. most of Norfolk, Bristol and Plymouth counties will fall below 32 degrees. Finally, last but not least, between 4 p.m. and 8 p.m., Cape Town and the islands freeze.

Precipitation becomes heaviest between 4 p.m. and 8 p.m. and from 8 p.m. to midnight the few remaining showers are over the extreme southeast of the Masse with just a few very light pockets of freezing drizzle elsewhere.

(WBZ-TV Chart)

I imagine by the evening drive most of the main roads will have some kind of ice treatment, which will make traveling a bit safer. Still, I would reduce speeds and definitely be wary of back roads, overpasses and typical colder spots.

Temperatures will continue to drop overnight into the teens for areas north and west of Boston, low 20s to the south and east.

We do not recover much on Saturday. Afternoon highs will be locked in the low to mid 20s despite good sunshine. Not much change at all on Sunday, the whole region is still stuck in the 20s, below zero. Thanks to some sunshine, despite the cold temperatures, some of the exposed ice will melt a bit during daylight hours this weekend, so you might be able to snack on a bit in the driveway.

(WBZ-TV Chart)

Finally, next week promises to be relatively quiet, just what the doctor ordered. Just a slim chance of a few rain showers brushing east of Mass on Tuesday, otherwise temps will be mostly in the upper 30s and 40s.