Snow lovers, you have a shot at redemption.
After last winter’s minuscule 0.4 inches of snow in Washington — the city’s third least snowy winter on record — initial outlooks are calling for significantly more of the white stuff this coming winter as well as dramatic swings in temperature.
Whereas last winter the storm threats were few and far between, forecasters are expecting this winter’s moderate to strong El Niño to help generate a more active wintry weather pattern, especially later in the season. Experts queried unanimously anticipate near or above-average winter snowfall for the city.
El Niño, however, is far from the only factor that can tip the scales toward — or away — from a snowy winter. El Niño is only one of several large-scale atmospheric patterns, known as teleconnections, that meteorologists consider when making seasonal forecasts.
Expert forecasters weigh in
We talked to five seasonal outlook specialists who are considering teleconnections and other factors as they develop winter forecasts. Their initial forecasts are relatively optimistic for snow lovers, especially compared to last winter’s paltry totals.
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Snowfall forecasts
All five forecasts are for near or above-average snowfall. Washington’s seasonal average is 13.7 inches.
- Judah Cohen, Verisk AER: 13.3 inches
- Todd Crawford, Atmospheric G2: 16 inches
- Paul Dorian, Arcfield Weather: 20 to 30 inches
- Paul Pastelok, AccuWeather: 14 to 18 inches
- Matt Rogers, Commodity Weather Group: 15 inches
The potential for cold and snow to favor the second half of the winter was a common theme. “That time of year is particularly productive for snowfall in this area,” Rogers said.
Temperature forecasts
The experts’ forecasts range from one degree above to as much as three degrees below Washington’s winter average of 39.7 degrees.
- Cohen: 1 degree above
- Crawford: Slightly above
- Dorian: 1-3 degrees below
- Pastelok: Slightly above
- Rogers: 1-2 degrees above
Key factors in winter forecast
The potential for a moderate to strong El Niño this winter has attracted the attention of forecasters because, on average, El Niño is associated with above-normal snowfall in the Mid-Atlantic. However, forecasters are uncertain whether El Niño will remain moderate or become strong. Its impacts can vary greatly depending on strength — moderate El Niño winters tend to be the coldest and snowiest, while strong El Niño winters tend to be the warmest and have winter snowfall ranging from almost nothing to a midseason blizzard.
“The stronger the El Niño is, the higher probability of it being a mild winter. But with the caveat that we have a small sample size for strong El Niños, so we might not fully understand the relationship,” said Cohen who expects the potential for “weather whiplash” because of temperatures swings.
Because of El Niño, Dorian is predicting a better chance than recent winters of at least one major East Coast storm. The return of El Niño “increases the chance for a ‘blockbuster’ snowstorm (or two) in the Eastern U.S., which hasn’t happened in the D.C.-to-Philly-to-NYC corridor since January 2016,” he said.
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El Niño and other teleconnections oscillate between warm and cool phases, or positive and negative phases, defined by fluctuations in ocean temperature, atmospheric pressure or wind, often at semiregular intervals. Each teleconnection can work alone or in tandem to increase or decrease the odds of cold and snow in the Mid-Atlantic depending on its phase.
Here are some of the various teleconnections forecasters are evaluating ahead of winter in crafting their seasonal forecasts:
Pacific Decadal Oscillation and Pacific North American patterns
The Pacific Decadal Oscillation (PDO) is a periodic fluctuation in sea surface temperatures across the northern Pacific Ocean. The PDO is currently in its negative phase, featuring warmer waters in the western and central portions of the northern Pacific, and cooler waters along the U.S. West Coast. It is expected to remain negative through winter, despite a sharp increase over recent weeks. Ordinarily a negative PDO might have forecasters leaning toward a warmer and drier winter in the eastern U.S., but El Niño can cancel out some of its influence.
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The Pacific North American (PNA) pattern is a periodic fluctuation in atmospheric pressure between the northern Pacific Ocean and North America. A negative PNA (which occurs more often during negative PDO patterns) typically results in mild weather in the eastern U.S. while a positive PNA can increase the odds of cold and snow. The PNA tends to change phase every week or two and typically can’t be predicted more than a few weeks ahead of time, although the positive phase usually occurs more often during El Niño.
North Atlantic Oscillation
The North Atlantic Oscillation (NAO) is a periodic fluctuation in atmospheric pressure over the North Atlantic Ocean. A negative NAO — lower pressure near the Azores and higher pressure across high latitudes such as Greenland — can increase the odds of cold and snow in the eastern U.S. The NAO can remain in the same phase a few weeks to a few months at a time and typically can’t be reliably predicted more than a few weeks ahead of formation. But the more often it’s negative, the better chances for cold and snow.
Quasi-Biennial Oscillation
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The Quasi-Biennial Oscillation (QBO) is a periodic fluctuation in winds in the tropical stratosphere. A negative QBO — winds in the tropical stratosphere blowing from east to west — can increase the odds of a colder winter in the Mid-Atlantic. The QBO is currently in the negative phase and is expected to remain negative through the upcoming winter.
And that’s not all
There are additional teleconnections over the Arctic, other parts of the Atlantic and Pacific oceans, and the Indian Ocean that can influence winter temperature and precipitation. Some research shows that Arctic sea ice, and even the behavior of October snow cover in Eurasia, can offer clues to the upcoming winter.
The uncertain strength of El Niño and mixed signals from other teleconnections can help explain the variation in the forecasters’ temperature and snowfall predictions.
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Dorian cited a negative QBO as a major factor in his forecast, the coldest and snowiest of the group. “Recent upper air observations from NASA radiosondes [weather balloons] suggest the ‘negative’ QBO phase will likely dominate during this upcoming winter season and this is strongly suggestive of colder-than-normal weather in the eastern U.S.,” he wrote in a detailed winter outlook.
Cohen called the mixed signals from teleconnections a “wild card” in the forecast, noting that “unimpressive” Eurasian snow cover “does not lend strong support for a colder/snowier winter” thus far, but that Arctic sea ice is “becoming more favorable” for colder weather.
“So in summary a tough forecast,” Cohen said.
Bottom line
We’ll probably be tracking more winter storm threats than last winter, especially later in the season, with the potential for snowfall much closer to average or even above average. The forecast remains more uncertain for temperatures, which will ultimately determine how much precipitation falls as snow in a region that perennially lives on the rain-snow line.
Stay tuned for Capital Weather Gang’s own winter outlook due out in the next week or two.
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