For the third time in two weeks, a powerful nor’easter is bearing down on the the Boston area. For the third time this winter, we’re using the term bomb cyclone to describe the storm.
But neither of those facts are what’s got meteorologists glued to their radar maps today. They’re watching the snow. There’s going to be a lot of it.
“This one’s main impact is going to be snow,” NWS meteorologist Kim Buttrick told the Associated Press of the storm.
A blizzard warning is in effect for coastal Massachusetts, where total snowfall accumulations of up to nearly two feet are expected. The snow is is falling fast, at rates of up to 1-3 inches per hour, which, combined with wind gusts veering well into tropical storm-force territory, sets the stage or whiteout conditions that could make travel “very dangerous,” the National Weather Service warns.
In Boston proper, more modest snowfall totals of 17 to 18 inches are expected. That’s still no fun to dig your car out of, mind you.
Boston is no stranger to snowy winters. ““We don’t see snowfall rates of 1-3 inches per hour every day in New England, but neither are they unheard of,” Weather Underground meteorologist Bob Henson told Earther via email. “Likewise, the expected accumulations are impressive but not necessarily record-smashing.”
But combined with the fact that this is the third nor’easter the region has seen in the past few weeks, and combined with the fact that meteorologists are already talking about a potential fourth, March 2018 is almost certainly going down as one of the snowiest in Boston’s history.
“We’re definitely seeing an anomalous event for this time of the year with respect to snowfall,” meteorologist Ed Vallee told Earther, noting that Boston’s number one snowstorm for March and April, on April Fool’s Day ‘97, saw about 22 inches of snow.
Vallee told Earther that the city has already seen seven inches of snow this month and that he’d add “at least another foot” after today’s storm.
“Especially late in the winter, it often takes a highly dynamic system to chill the atmosphere to snow-producing temperatures, and those strong dynamics can also lead to very heavy snowfall rates,” Henson said.
So let’s talk about those dynamics a bit. Henson told Earther the volley of storms we’ve seen in recent weeks is likely connected to a record strong phase of the Madden-Julian Oscillation, which NOAA describes as “a major fluctuation in tropical circulation and rainfall that moves eastward along the equator and circles the entire globe in a span of 30–60 days on average.”
This atmospheric disturbance is distinct from the El Nino Southern Oscillation, which is stationary in the tropical Pacific.
As Henson explained, a strongly active MJO “fed into a split of the stratospheric polar vortex in February” that’s still having atmospheric reverberations, including the recent “Beast from the East” cold outbreak over Europe and record cold in Siberia. The MJO is also a strong contributor to Arctic air outbreaks across the central and eastern U.S., according to NOAA.
In addition to the legacy of the MJO, another atmospheric pattern called the North Atlantic Oscillation (NAO) veered into record low territory earlier this month. A negative NAO is characterized by a ridge of high pressure air over Greenland, something meteorologists call the Greenland block.
Vallee explained that the Greenland block leads to a trough of low pressure further south and west. “That’s a very conducive pattern for nor’easters to form,” he said, noting that the Greenland block not only enhances the pressure gradient fueling these storms, but can slow their progress out to sea.
The nor’easter that drove massive coastal flooding in Boston at the beginning of the month was slow to get out of the city’s way thanks to the Greenland block, Weather Underground reported at the time.
This time around, at least, the coastal flooding risk for Massachusetts is fairly low. Weather Underground reports that the strongest winds from today’s nor’easter will be further offshore, with peak land gusts of about 60 miles per hour forecast to blow across Cape Cod and Nantucket.
This storm, unlike its predecessors, also happens to coincide with some of the lowest astronomical tides of the month.
So, while Massachusetts will wind up buried in snow today, at least folks’ basements won’t be flooding, too? Small miracles, I guess.