Frigid air led to record-breaking snowfall in US Northeast

Washington [US], December 19 : The 30 to 45 inches of snowfall in a 350-mile swath from north-central Pennsylvania to New Hampshire has created a new record that will be studied for years to come.
While the meteorologists were not expecting three and a half feet of snow, according to a report by The Washington Post, a number of records were set in the past days, including what is potentially Pennsylvania's greatest 24-hour snowfall, 43.3 inches in Alba, a small town in the north-central part of the state.
Despite the quantity and the speed of snowfall that led to vehicles being buried and roadways disappearing in at least four states, surprisingly there were no power outages seen, except for about 30,000 ice-related outages in Virginia.
While during the winter season the word "bombogenesis" is generally used for most of the Northeast's storms, the storm on Wednesday was nothing of this nature. It was rather a weak system but had plenty of moisture to work with, contributing to a localized zone of extreme snowfall, The Washington Post said.
"The four to five-inch an hour rates observed in this event are extremely rare...It's even rarer to sustain such snowfall rates for several hours (about 5 hours in this case)," said Alex Lamers, a meteorologist at NOAA's Weather Prediction Center.
The Washington Post quoted Jared Klein, a meteorologist at the Binghamton Weather Service office, as measuring 3.2 inches in 5 hours, 31.7 inches in 9 hours, 36.5 inches in 12 hours, and 41 inches in 18 hours at his home nearby.
Meanwhile, the snow on Wednesday and Thursday was fluffy that soon stacked up. "The warmer the temperature, the more likely there will be supercooled water (liquid water at temperatures below freezing) that 'sticks' (refreezes) to the snowflake. This makes snow more dense," Lamers was quoted as saying.
He further said, "Temperature and moisture also affect the natural structure of snowflakes...It turns out the 'fluffiest' snowflakes (called "dendrites") commonly form with high humidity and temperatures between zero and 10F."
He said that the wind can "create stresses that fracture snowflakes as they fall, making them smaller and denser as they reach the ground" leading to fluffy snowfall.
During the height of the snow in Binghamton, the temperature hovered between 15 and 16 degrees, with dew points -- a number that corresponds to how much moisture is in the air -- at 12 or 13 degrees meaning that the air was frigid but also nearly saturated, the perfect recipe for dry fluffy snow, The Washington Post said.
While these factors led to hefty snowfall, but the reason behind "lone, stubborn snow band" lies in temperature "but at the mid-levels of the atmosphere," Matthew Cappucci, the author of the article opined.
He said, "Between roughly 5,000 and 10,000 feet, a sharp temperature gradient, or change with horizontal distance, existed over the northern Appalachians. That "frontogenesis" acted akin to a cold front, as the focal mechanism to lift the air and squeeze the moisture out of it. That band didn't move much with time; instead, it pivoted as the instigating storm system swept northeast offshore of New England."
The stretching at the mid-levels because of converging air, called "deformation," helped enhance upward lift in the lower atmosphere, Cappucci explained.
"This stretching, or pulling apart of air at the mid-to-upper levels, has a vacuum-like effect; the air is forced to rise from below to fill the newly created void. That, combined with other factors, helped kick the snow band into overdrive," he added.