It would all come down to timing.
As temperatures plunged from the balmy 50s to the low teens on Monday, Massachusetts Department of Transportation crews waited for the perfect moment to treat the roads to ward against ice. Start too early, and the salt would be washed away by rain. Start too late, and ice would have a chance to glaze the pavement before crews could reach the region’s major roadways.
“We’d hate to have it all literally wash down the drain,” said Frank DePaola, highway administrator for the state Department of Transportation. “We’re watching the weather forecast very closely.”
Transportation officials monitored temperature sensors embedded in the roads through the day, waiting for that magic number, 32 degrees, to appear on the thermometer, the starting gun that would trigger herculean efforts from the region’s transportation and public utilities crews to fend off the ice.
Just after 7 p.m. they struck, as a cold front began ushering in a “polar vortex” that was expected to bring temperatures down to near-record levels.
In Boston, temperatures dropped 20 degrees between 3 p.m. and 5 p.m. The speed at which weather morphed from pleasant to frigid left crews with a narrow window before ice began to form.
Rebecca Gould, a meteorologist with the National Weather Service, said Tuesday morning temperatures would probably not reach higher than 12 degrees. The 44-degree difference between Monday midday and Tuesday morning was expected to make ice on roads and pavement a significant problem.
The forecast contained one saving grace, Gould said: As the cold front moved through Massachusetts Monday night, she expected winds to be quite gusty, which she said would dry out much of the water that accumulated from rain and melting snow Monday afternoon.
Though the winds are expected to be of some help, they will not be enough to prevent some ice. “Given the amount of water I saw on the roads today, probably there’s still a danger of icy conditions,” Gould said.
And Tuesday’s forecast?
The expected high for Tuesday was 17 degrees, though it will feel like minus 6 degrees because of the brisk winds.
“Brrrrrrrrrrrrrr,” Gould said. “And you can quote me on that.”
The iciness expected in Boston this week is reminiscent of stories from more than a century ago.
“Hard work to walk,” detailed one Boston Globe reporter in a January 1899 story. “Boston’s sidewalks again cover with ice. Combination of drizzle and freeze a woe to pedestrians. Skates the safest means of getting about. The city was like one vast bowling alley, the human pins going down in every direction.”
A little more recently, a snowstorm in February 1934 “rendered plows and snow loaders useless.” After city employees grew exhausted at efforts to battle the snow, Boston’s public works commissioner temporarily hired 880 unemployed men to carry pick-axes through the streets to break apart the ice and cart away the chunks.
Anti-ice efforts were a bit higher-tech on Monday.
Four hundred employees of the Massachusetts Department of Transportation were on call for de-icing duty Monday night. Boston’s Department of Public Works had 150 pieces of equipment on the roads for salting efforts.
As the mercury dropped, work crews focused on elevated roadways — Interstate 90 close to Boston University, Interstate 93 as it cuts through Somerville, major bridges — because they freeze more quickly as cold air runs over and under the bridges.
The Massachusetts Bay Transportation Authority made preparations, too.
Trains on the Red, Orange, and Blue lines were equipped with scrapers that clear the third rail of icy buildups, MBTA spokeswoman Kelly Smith said.
The trains are also outfitted with ice cutters during the winter to keep overhead wires ice-free.
Crews planned to treat parking lots and platforms with salt and sand, Smith said.
Because the initial freezing would happen during peak service Monday evening, the steady train traffic was expected to keep tracks clear of icy buildup Monday night.
“Overnight, we will be exercising the trains on all lines to keep them moving and functioning for the morning commute,” Smith said.Martine Powers can be reached at email@example.com. Follow her on Twitter @martinepowers.