By around Dec. 8, weather systems in Alaska and Greenland may configure themselves to allow frigid air to pour southward over eastern North America. And with cold air in place, the potential for snow would markedly increase.
Such a pattern is not yet locked in, and the models could be wrong, but it has captured the attention of meteorologists who specialize in long-range forecasting.
“The pattern looks impressive to me,” said Capital Weather Gang’s Matt Rogers, a long-range forecaster. “I haven’t seen anything like this in a while.”
Wes Junker, Capital Weather Gang’s winter-weather expert, called the pattern “very favorable for wintry weather in the eastern two-thirds of the country.”
Groups of simulations from the European and American weather models show twin areas of high pressure parked over Alaska and Greenland between Dec. 8 and 16, possibly longer. Like two massive boulders placed in a fast-flowing stream, these high pressure zones — sometimes called blocking highs — would force Arctic air south into eastern North America.
The flow would potentially unleash pieces of the so-called polar vortex, the meandering ring of icy air encircling the North Pole.
Mid-latitude land areas all around the Northern Hemisphere could be affected. Judah Cohen, a seasonal forecaster at Atmospheric and Environmental Research, tweeted “it’s been at least five years” since he’s seen such a wintry looking pattern forecast for the eastern U.S., Europe, and east Asia simultaneously.
Such a pattern screams winter-weather potential. Similar patterns in the past have led to some extremely cold and/or snowy results. December 1989 and 2009, for example, featured the kind of arrangement of weather systems the models are simulating. December 1989 was historically cold while December 2009 produced a record-setting snowstorm in the Mid-Atlantic known as Snowpocalpyse.
The pattern predicted is exactly the kind Junker said was needed for a cold and snowy winter in Washington when he wrote the piece “Here’s one way D.C. could get a lot of snow in the winter” two weeks ago. The pattern is illustrated in the right panel of the image below, and closely matches the pattern forecast Dec. 8 to 13.
But it’s not a sure thing the pattern will materialize, Junker stressed. It’s too soon to say how cold it will be and exactly where and when any storms, which could turn into snow-producers, will form and track. “The models at this time range still aren’t very good, even if they’re consistent,” Junker said.
Rogers said that by later this week, forecasters should have better confidence in the outlooks. Right now, models are trying to capture a pattern 11 to 15 days into the future when they don’t have a track record of great accuracy, but they become more skilled six to 10 days away.
If the pattern comes together, the next question is how long will it persist. Rogers said the models suggest it could hang around until around Christmas. If the Alaska and the Greenland blocking highs form, “the pattern becomes a lot more durable”, he said. Last December, a blocking high formed over Alaska but not Greenland, and the resulting cold only stuck around about 10 days.
Beyond Christmas, assuming the pattern becomes established, it’s hard to say what will happen next. A La Niña event, indicated by colder-than-normal water in the tropical Pacific Ocean, is underway, and past such events have featured “a lot of winter-weather volatility,” Rogers said.