Snow covers parts of the Mid-Atlantic and the Northeast the morning after the Blizzard of 2016, January 24, 2016

The incredible snowstorm that buried parts of the East Coast this past weekend lived up to the hype and even exceeded expectations. Likely to be remembered as a benchmark for decades, the blizzard dropped more than a foot of snow across parts of nine states from Kentucky to New York between January 21 and January 23. Here’s a look at how this historic blizzard came to life, and why it produced so much snow.

One of the ways this was truly an unusual winter storm is that meteorologists were able to confidently predict its path and impacts almost a week ahead of time. The weather models began consistently showing a snowstorm of this magnitude the weekend before the flakes started flying. This consistency in the weather models allowed meteorologists to confidently warn the public well ahead of the storm, giving people more time than usual to prepare.

The GFS weather model’s forecast for the jet stream on Friday, January 22, 2016, showing a deep trough sitting over the eastern halves of the United States and Canada. Image credit: Tropical Tidbits

The blizzard formed from a disturbance that came ashore in the Pacific Northwest on Wednesday, January 20. The disturbance quickly moved east, and a sharp trough in the jet stream developed as the feature made its way east over the Rocky Mountains the following day. A trough is an elongated area of lower air pressure—the lift produced by the combination of a trough and strong winds in the upper levels can lead to the development of a low-pressure system at the surface.

After producing heavy snow and ice in the Mid-South, the system approached the Mid-Atlantic and began to develop into a nor’easter off the coast of the Carolinas. Tapping the right mixture of cold air flowing south and moist air surging north from the tropics, the impressive storm cranked out heavy snow that continued for more than 24 hours in the hardest-hit spots.

Water vapor imagery on January 23, 2016, shows dry air (orange/red) swirling into the low-pressure system that produced blizzard conditions from Washington D.C. to New York City. image credit: NASA

The blizzard is a classic example of a nor’easter, or an intense low-pressure system that moves parallel to the East Coast with strong winds and heavy precipitation. The northwestern part of a nor’easter is the classic “comma head” that makes these storms look so ominous and beautiful on satellite imagery, as seen in the water vapor image above.

This comma head, known as the “deformation zone,” is a region of the storm where intense dynamics in the atmosphere create very heavy bands of snow that can linger over the same communities for many hours at a time. This blizzard was a textbook example of how the deformation zone in a nor’easter typically sets up along and west of Interstate 95 during major storms.

A comparison between the National Weather Service (NWS) Weather Prediction Center’s snowfall forecast the night before the blizzard and observed snowfall totals. Image credit: Dennis Mersereau

Both forecasters and the guidance produced by weather models did a good job pinpointing the bulk of the heavy snow near Washington, D.C., but they fell short in that neither humans nor a majority of weather models predicted that the very heavy snow would extend as far north as it did. The northern edge of the snow was always predicted to be very sharp, with just a few dozen miles separating a dusting and crippling amounts of snow in most cases. Sleet and freezing rain on the south side of the storm also kept final totals down.

New York City quickly bypassed its original predictions of 6 to 12 inches of snow, ultimately seeing more than 2 feet of snow across the city by the time the skies cleared out. This is in sharp contrast to a storm in January 2015 where predictions of up to two feet of snow there fell short after that nor’easter shifted a few dozen miles to the east, proving that the track of a storm is everything when it comes to major snowstorms on the East Coast.

National Weather Service analysis of observed snowfall totals from the Blizzard of 2016. Image credit: Dennis Mersereau

Snowfall records fell across the region as the white stuff piled up. New York City’s JFK Airport was the blizzard’s surprise winner among the major cities, recording an astounding 30.5 inches of snow by the end of the storm, which is an all-time record for the site. The city’s LaGuardia Airport, about 10 miles to the northwest of JFK, also shattered its all-time record with 27.5 inches. The weather observing station in Central Park fell one-tenth of an inch shy of tying its all-time snowfall record of 26.9 inches, falling just a few flakes short of unseating a snowfall in February 2006 as the top event. 

The blizzard was the second-largest on record at Washington, D.C.’s Dulles Airport, dropping 29.3 inches of snow at the airfield that sits about 25 miles west of the city. Washington’s National Airport, just across the Potomac River in Arlington, Virginia, is facing a bit of controversy after weather observers at the airport improperly measured the snow, losing a snowboard required to accurately take measurements every six hours. The site reported 17.8 inches of snow, which will stand as the airport’s official total despite really having had more snow than that. The CoCoRaHS weather observer at The White House a couple of miles away measured 21.9 inches of snow from the nor’easter.

The snowstorm was the largest ever recorded at Baltimore’s international airport, blowing past the old record of 25.2 inches with a final measurement of 29.2 inches. Philadelphia, no stranger to major winter storms, didn’t crack the top five this time around, but it ended up with a formidable 22.4 inches of snow by Sunday morning nevertheless.

Snow wasn’t the only hazard presented by the storm. Strong winds coinciding with a full moon led to extensive coastal flooding at high tide. Parts of Delaware and New Jersey recorded record high storm surges from the blizzard, and the surge in Cape May, New Jersey, was higher than that recorded when Hurricane Sandy came ashore in 2012.

The blizzard will likely rank as a category four—or “crippling”—on NOAA’s Northeast Snowfall Impact Scale (NESIS), a five-category index used to objectively rank the impact of snowstorms in the northeastern United States based on the number of people affected by heavy snow. Pending the final results, the last time we experienced a NESIS Category Four snowstorm of this magnitude was the President’s Day Blizzard of 2003, likely placing it in the top five of all storms ranked with the scale since 1956.