In the winter of 2015, the northeastern United States received an unprecedented amount of snow and freezing temperatures. Boston, in many ways at the epicenter of the event, received a record-breaking 110 inches of snow (the previous record had been 107). Strong storms pummeled various parts of the country: in Colorado, at Wolf Creek Pass, which crosses the Continental Divide, 23 inches of snow came down within twenty-four hours. At the same time, temperatures plummeted: Whiteface Mountain, part of the Adirondack Mountains in New York State, measured a record –114°F. New England was battered in February by a series of Nor’easters that piled snowdrift upon snowdrift.
Nor’easters can do some real damage when a high-pressure system over New England or the northern Atlantic blocks the northern progression of a low-pressure system. As the low stops moving, its counterclockwise winds meet the clockwise gusts of the high-pressure system, battering the coastline with severe winds.
A Nor’easter storm, which begins as a low-pressure system over warm Gulf Stream waters, forms off the East Coast of the United States and moves northward into New England. These storms usually form between October and April, and as they move up the coast and encounter frigid arctic air flowing down from Canada, instability increases and the chance for heavy snow and gale-force winds is great. Most Nor’easters don’t turn into major storms, but the ones that do, such as those of 2015, live in memory and folklore for generations.
As the severe winter continued across the country, nightly television viewers were increasingly treated to comments about a “polar vortex.”
A polar vortex refers to an area of low pressure that forms near one of the poles. At the North Pole it rotates counterclockwise; at the South Pole, clockwise. Polar vortices are normally more active in the south than in the north, but 2015 presented a meteorological anomaly. The vortex probably caused temperatures across much of the northern part of the country to drop anywhere between 15°F and 35°F.
In practical terms, this meant that very little of the heavy snowfall that came down across the Northeast and Upper Midwest had a chance to melt. Instead, it piled up, defying efforts to clear it.
An additional feature of polar vortices is that they tend to deplete the ozone layer, since their chemical composition creates chlorine, a gas that causes the ozone layer to dissolve. This has created a hole in the ozone layer near the South Pole.
The strength of vortices can be increased by volcanic eruptions or by El Niño (for details, see the section dedicated to El Niño). The latter is probably responsible for the intensified northern polar vortex in the winter of 2014–2015, which brought so much misery to those living in the northern parts of the United States.