Forecasters expect more snow than last winter in Washington, D.C.

We interviewed via email seven forecasters who either own forecasting businesses or represent larger companies. All but two predicted just 10 inches or so for the winter. The two outliers are calling for more than 20 inches, offering a glimmer of hope for area snow lovers.

Most of the forecasters we queried named La Niña as the primary reason snow amounts may be somewhat depressed.

During La Niña events, characterized by cooler than normal ocean waters in the tropical Pacific Ocean, the prevailing storm track is typically north of Washington. Such tracks draw in mild air when precipitation threatens, meaning more wintry-mix events and rain, rather than snow. Also, storms that track north of Washington usually produce less precipitation than storms that come up from the south.

Historically, La Niña winters have produced slightly less snow than El Niño winters, when storms more frequently approach from the south.

Five of the seven forecasters we reached out to called for a milder-than-normal winter for the sixth season in a row. (Our last colder-than-average winter was in 2015.) However, several noted that while La Niñas often draw mild air into the area, they can be volatile and sometimes involve brutal blasts of Arctic air.

The official outlook from the National Oceanic and Atmospheric Administration favors a milder than normal winter in Washington, largely due to the La Niña influence on the prevailing storm track.

The two forecasters who called for snowy and/or cold winters pointed to the fact that the configuration of weather systems in the northern Pacific Ocean and high latitudes, from Alaska to Greenland, can override the effects of La Niña. They see early indications this could be the case in the upcoming winter.

The Capital Weather Gang will issue its outlook for the 2020-2021 winter in early November.

Below, we summarize the outlooks from the seven meteorologists we contacted:

Joe Bastardi, WeatherBell

Predicted snowfall: 10 inches

Temperatures: Somewhat above normal, by two degrees

In his outlook (behind a paywall) posted at the end of September, Bastardi writes that the basis for his forecast is the historical behavior of developing (first-year) La Niña events. While they’re associated with warmer than normal weather in the Mid-Atlantic, he says they often feature “big cold outbreaks” and are volatile.

“This is kind of a high-risk forecast,” he writes. “I am more concerned about a colder, rather than a warmer look, in the longer term.”

Regarding snow, Bastardi cautions, “even in warm winters, one or two storms … can sneak in and provide significant snowfalls.”

Todd Crawford, the Weather Company (owned by IBM)

Predicted snowfall: 7 inches

Temperatures: Above normal

Crawford said he believes La Niña will suppress snowfall. “The last 8 La Niña winters have seen snowfall totals range from 2 to 14 inches, all 8 events *below* the standard 30-year normal of 15 inches,” he writes. He adds that zones of high pressure in the high latitudes required for sustained cold will be “relatively infrequent” if computer models are correct.

Judah Cohen, Atmospheric Environmental Research

Predicted snowfall: 9 inches

Temperatures: Near normal

For over a decade, Cohen has worked to refine his winter outlooks by investigating how snow cover in Siberia and sea ice in the Arctic during autumn influences the winter stability of the polar vortex. When the polar vortex fractures or weakens, it favors frigid outbreaks of Arctic air into North America, including the Eastern United States. His hypothesis is that above-normal Siberian snow cover during October increases the likelihood of polar vortex disruption in the winter.

Cohen sees signs that snow cover in Siberia will increase later this month. “It is early in the process but the prospects for a PV [polar vortex] weakening look intriguing based on the weather forecasts,” he writes.

Paul Dorian, Perspecta Weather

Predicted snowfall: 20.5 inches

Temperatures: Slightly colder than normal

Despite La Niña, Dorian says, numerous factors point to an alignment of weather patterns over the oceans and high latitudes that will favor cold, snowy weather. “Many signs point to colder than normal conditions … and the virtually snowless winter of last year is quite likely not going to repeat itself,” he concludes.

Paul Pastelok, AccuWeather

Predicted snowfall: 10 inches (range of 7 to 12 inches)

Temperatures: Above normal

Pastelok says La Niña is the main driver of AccuWeather’s forecast, and he foresees fast-moving “clipper-like” weather systems zipping across the northern United States. Usually, these don’t contain much heavy precipitation and produce little snow in Washington. In the second half of the winter, he says, juicier systems may track from the Southern Plains to the Ohio Valley, but that would place the Mid-Atlantic on the mild side of storms. He cautions there’s a chance that warm waters offshore in the Pacific Northwest might shift the storm track to bring colder and stormier conditions to the Mid-Atlantic but that as of now, “this is just a risk.”

Matt Rogers, Commodity Weather Group

Predicted snowfall: 10 inches

Temperatures: Somewhat above normal (by one to two degrees)

Rogers says to expect a winter “both colder and snowier than last year, but also still marginally warmer and less snowy than the 30-year normal.” Historically, he says, La Niñas start off cold but trend milder during the second half of winter. He anticipates plenty of volatility. “If you don’t like the weather one week, just wait one and we’ll probably flip it again!” he writes.

(Note: Matt Rogers is also a contributor to the Capital Weather Gang.)

Dave Tolleris, WxRisk

Predicted snowfall: 22 inches

Temperatures: Near normal

Tolleris warns it is a “mistake” for forecasters to solely rely on La Niña in their outlooks and that other factors support a snowy forecast. Notably, he says, warm ocean temperatures offshore in the Pacific Northwest are “dramatically different from anything I have seen over the last 20 years.” If these warm waters persist, Tolleris expects a zone of high pressure to build over the Western United States, which would cause the jet stream to dive south in the East. “This would … favor below-normal temperatures and a stormy weather pattern,” he writes.

Contrary to Rogers, Tolleris says winter will start off quite mild in December and January but turn much colder in February and March as he expects La Niña to rapidly weaken and its influence to wane. “There is some correlation to weakening La Nina events during the second half of the winter season into the spring that produce really cold weather patterns and usually moderate or above-normal snowfall in the Eastern U.S.,” he says.

Source Article