The Nugget Newspaper - News and Opinion from Sisters, Oregon

After enduring one of the worst fire seasons in modern history, Oregonians earnestly hope the upcoming winter will deliver an ample supply of much-needed moisture to extinguish the fires still burning and to ease extreme drought conditions that grip our region.

Every source of information begins by revealing current conditions in the central Pacific Ocean. Known as the El Niño Southern Oscillation (ENSO), it is the most important climate phenomenon on earth due to its ability to change the global atmospheric circulation. It exists in one of three phases: warm (El Niño), cold (La Niña) and neutral (sometimes referred to as La Nada).

In recent months, lower sea surface temperatures and an increasing trade wind have shifted the ENSO phase from neutral to a weak La Niña, and most forecasters think it will strengthen through the upcoming winter. In fact, based on the latest data, the Climate Prediction Center has said there’s an 85 percent chance of a moderate-to-strong La Niña to be in place by the November-January time frame. This is good news if you like your winters cooler and wetter than normal.

As a rule, the southern tier of states experiences warmer and drier than normal conditions during a La Niña regime, while the northern part of the country tends to be cooler and wetter, except for New England where this correlation is weaker. An active jet stream should direct several Pacific storms into the Northwest. At the same time, colder than normal air usually overspreads Western Canada, allowing for possible cold snaps when high amplitude troughs develop in the upper atmosphere.

A team of long-range forecasters at AccuWeather, led by Senior Meteorologist Paul Pastelok, recently released their winter outlook. An early start to wintry weather is expected in the Pacific Northwest.

“Mountain snow and stormy conditions may arrive in late fall for the Northwest, northern California, and northern Rockies.

“Even the I-5 corridor from Medford through Seattle will have several opportunities for accumulating snowfall before 2020 draws to a close,” Pastelok said.

The winds that circulate about the polar vortex will probably be weak in the late fall and early winter, and again in late winter, may allow excursions of arctic air into the U.S. During mid-winter, these winds should strengthen, keeping the coldest air confined to the polar regions, according to the AccuWeather team.

Pete Parsons, meteorologist for the Oregon Department of Forestry, issued his October through December outlook on September 17, 2020. He foresees normal temperatures and precipitation levels for the three-month period in Central Oregon.

Parsons relies heavily on analog forecasting — selecting past years that most closely match current ENSO values and trends, then extrapolating forward the type of winter that occurred in those years. For this forecast he used a blend of three analog years, 1959, 1970 and 1995.

“In La Niña years, it usually doesn’t get a lot wetter until November. But you start to see some significant cooling in October,” said Parsons.

Parsons believes higher-than-normal amplitudes in upper air patterns will likely emerge this winter.

“There are a lot of indicators that are pointing us to a cool, wet fall and colder, stormier winter for Oregon,” he adds.

The National Weather Service’s Climate Prediction Center issued its forecast on September 17, 2020 for the period October through December. It calls for warmer than normal temperatures and above normal precipitation in our area. By January through March of 2021 there’s an equal chance that temperatures will come in above or below normal, but it be wetter than average.

Nearly all the prognosticators agree that a robust La Niña is on the way that should produce a cooler and wetter winter, with ample snow in the mountains here in the Pacific Northwest. And we sure could use it.