Why the West Got Buried in Snow, While the East Got Little

This year’s snow season is a tale of two starkly different winters: A cold and snowy one in the West, and a warm and relatively snowless one in the East.

The Western United States received a lot more snow than usual this season, much of it unleashed by punishing storms that battered California especially hard throughout the winter. Parts of the Eastern half of the country, however, saw much less snow than normal amid unusually warm winter temperatures.

It’s not uncommon for the two coasts to experience opposing weather conditions. This can happen when the jet stream, a band of winds that blow from west to east around the planet, starts to meander into a wavelike pattern. This wind pattern results in cooler conditions where it dips southward and warmer conditions where it arcs northward.

The timing of precipitation and freezing temperatures also influenced this year’s unsettling winter season, said Karin Gleason, a climate scientist for the National Oceanic and Atmospheric Administration.

In some cases, precipitation just happened to fall at the same time that temperatures were cold enough for snow to form, Ms. Gleason added. But, if temperatures were too warm, more precipitation may have fallen as rain, rather than snow.

“It’s a conspiring of different factors,” she said.

A Cold, Snowy Winter for the West

Percent of average cumulative snowfall

A succession of atmospheric river storms pummeled Western states from late December to January, and again in March. These storms were largely responsible for dumping record amounts of snow across much of the West. The Western United States also experienced colder-than-normal temperatures this winter, which helped snow to fall and stick to the ground.

Some of that winter snow fell at unusually low elevations, from a range of 500 to 2,000 feet, a rare sight in regions like the hills overlooking the San Francisco Bay Area. Warming temperatures over the past decades have generally resulted in snow that is concentrated at colder, higher elevations, said David Simeral, a research scientist with the Desert Research Institute.

Colder-than-normal temperatures across much of the West also helped build up and sustain a deep snowpack in California’s Sierra Nevada and parts of the intermountain West, including northern Arizona, western Colorado, Nevada and Utah.

April 1 is a benchmark date for when water managers expect snowpack to peak. On that day, the average statewide snowpack levels — as measured by the amount of liquid water available in the snow — were more than double the historical average for California. In the southern Sierras, which generally receives less snow, average snowpack levels reached 62.6 inches, nearly triple the historical amount.

Healthy snowpack and replenished reservoirs have helped ease California out of its long-term drought, the driest three-year stretch on record. The extremely wet Western winter has also improved the long-term precipitation shortfalls that had accumulated over several years, bringing parts of western Oregon, southern Idaho, Nevada and central Utah out of extreme drought.

Though the record-deep snowpack will bring welcome water supply benefits to large swaths of the West in the spring, it also poses a greater risk of flooding as the snow melts, especially if temperatures rise quickly.

A Warm, Rainy Winter for the East

Percent of average cumulative snowfall

A different pattern occurred in the East, where snow has been elusive for many cities that regularly expect it. Instead, warmer-than-normal winter weather brought more rain than snow.

After 328 consecutive snowless days, New York City finally recorded 0.4 inch of snow on Feb. 1. Baltimore, Philadelphia and Washington, D.C., also went more than 300 days without measurable snow — defined as at least a tenth of an inch.

“This winter hasn’t been unusual in terms of total precipitation,” said Aiguo Dai, an atmospheric science professor at the University at Albany, SUNY. But the warmer weather has meant that more precipitation than usual in the Northeast has fallen as rain, rather than snow, Dr. Dai said.

The phenomenon is known as a warm snow drought, and it is likely to occur more frequently as a result of warming temperatures, experts say.

When temperatures were cold enough, precipitation did not always fall in large amounts, which was the case when a bitterly cold wind chill gripped the Northeast in early February.

Though much of the Northeast urban corridor had been spared harsh winter weather this season, a deadly blizzard early in the winter dumped several feet of snow in Buffalo. Snow also piled up in portions of upstate New York, northwestern Massachusetts and southern Vermont in a winter storm in mid-March.