Snow falls at the U.S. Capitol in Washington on March 21. (/J. Scott Applewhite/AP)

December is a little more than a month away and, before we know it, forecasters will be tracking winter storm threats. If long-range prognosticators in the private sector are correct, these threats will come often.

We reviewed winter outlooks from six organizations, and the consensus is that this winter will be snowier than normal in Washington. In fact, all of them predicted 20 to 30 inches of snow, which is substantially more than the average of 15.4 inches.

The primary rationale for the snowy outlook is that an El Niño event is expected to develop, and, on average, more snow falls during El Niño in Washington than during its opposite phase, La Niña.

The snowy predictions, culled consulting meteorologists and companies such as AccuWeather and the Weather Company, differ some from the National Oceanic and Atmospheric Administration outlook, which was less enthusiastic about the snow potential.

Although the NOAA outlook gently leans toward above-normal precipitation in the Washington region, it wasn’t too bullish on snow prospects. Mike Halpert, deputy director of NOAA’s Climate Prediction Center, told reporters that snowfall has typically averaged near to below normal in Washington during weak El Niños. (Note that NOAA does not produce an official snowfall forecast, just a general precipitation and temperature outlook.)

The strength of the El Niño event, assuming it develops, could play a key role in how snowy our winter ends up. Although weak El Nino events haven’t — on average — produced especially snowy winters, several of our snowiest winters on record have coincided with moderate to strong El Niños. These bigger El Niño events tend to help fuel storms that track across the southern United States and turn up in the East Coast.

NOAA is calling for a weak El Niño, but some computer models suggest a moderate event could develop.

Paul Dorian, meteorologist with Perspecta Weather, noted it’s not just the strength of El Niño that matters for the snowfall outlook, but also its particular location in the tropical Pacific Ocean. In his outlook, he noted that this is El Niño is likely to be “most pronounced” in the central tropical Pacific which increases chances for a snowy winter.

“In recent history, strong El Nino’s that were ‘eastern-based’ generally have been associated with warmer-than-normal winters in the eastern US whereas “centrally-based” weak-to-moderate El Nino’s have been often correlated with cold and snowy winters,” he wrote.

Many of the other private-sector outlooks we reviewed pointed to additional factors that could tilt the odds toward more snow, irrespective of El Niño.

Paul Pastelok, long-range forecasting specialist at AccuWeather, said both El Niño and a sprawling area of warm waters in the Northeast Pacific Ocean, sometimes referred to as “the blob” — would favor a cold, stormy pattern in the Mid-Atlantic.

“I see a favorable track this year for snow across the northern-central Mid-Atlantic from D.C. to southern Pennsylvania into New Jersey,” Pastelok said in an email.

Dorian along with Dave Tolleris, who runs the WxRisk forecasting company, and Matt Rogers, president of the Commodity Weather Group, agreed that this blob could configure the jet stream in a favorable position to deliver cold air to the eastern United States — which is necessary for snowstorms.

Tolleris, Rogers, Dorian, and Todd Crawford, senior meteorological scientist at the Weather Company, mentioned the sun as another factor that could boost snow prospects. The sun is approaching a minimum intensity in its 11-year cycle. Some winters near such a solar minimum have featured cold and stormy conditions such as in 1995-96 and 2009-10.

Crawford and Rogers predict that the winter may begin on the mild side but come on strong in January and February.

“We expect a sharp reversal to colder and stormier conditions after the New Year and especially by February,” Crawford said in an email.

Another check in the column for a cold, snowy winter? The European weather prediction model, Tolleris said.

“The last four runs of the European model have shown an extremely bullish signal for a cold and snowy winter,” he said in email. He added that the UKMet forecast model is also in the European model’s camp.

Joe Bastardi, chief forecaster for WeatherBell Analytics, shared similar ideas to the other forecasters in his outlook. He concluded that the upcoming winter could resemble those of 2002-03 and 2009-10, which both featured blockbuster snowstorms in Washington.

Collectively, the forecasts from the groups we reviewed showed remarkable similarity. But some groups have yet to release their outlooks and the reliability of such long-range forecasts is limited. There can be, and often are, surprises. The Capital Weather Gang’s official winter outlook will be released in the next two weeks.

Outlooks by the numbers

Keeping in mind Washington’s average snowfall is 15.4 inches, here’s what various private sector organizations predict:

Joe Bastardi, WeatherBell:

  • Snowfall prediction: 25 inches in Washington, 34 inches at Dulles
  • Temperature forecast: Colder than average

Todd Crawford, the Weather Company:

  • Snowfall prediction: 23 inches in Washington
  • Temperature forecast: Slightly colder than average

Paul Dorian, Perspecta Weather:

  • Snowfall prediction: 25 inches+ in Washington
  • Temperatures forecast: Colder than average

Paul Pastelok, AccuWeather:

  • Snowfall prediction: 30 inches in Washington
  • Temperature forecast: Near average

Matt Rogers, Commodity Weather Group

  • Snowfall prediction: 23 inches in Washington
  • Temperature forecast: Colder than average