An El Nino likely will make the Pacific Northwest warmer than normal this winter and cause drought to persist east of the Cascade Range, the National Oceanic and Atmospheric Administration predicted Thursday, Oct. 19.

An El Nino shifts the Pacific jet stream, meaning the northern U.S. will get less cold air than usual from upper Canada and the North Pole, NOAA chief forecaster Jon Gottschalck said.

“The anticipated strong El Nino is the predominant factor driving the U.S. winter outlook this year,” he said.

“The greatest odds for warmer-than-average conditions are in Alaska, the Pacific Northwest and northern New England,” he said.

An El Nino is triggered by warm Pacific Ocean temperatures along the equator. The last El Nino was in 2019. A La Nina, triggered by cool seas, prevailed the past three winters.

NOAA rates the chances of a strong El Nino forming at 75% to 85%. The El Nino can be expected to have its strongest impacts in January, February and March, according to forecasters.

Northwest snowpacks have varied during previous El Ninos. Washington’s 2014-15 “snowpack drought” occurred during an El Nino. The El Nino was stronger the next winter, but the snowpack was above average.

NOAA Chief Scientist Sarah Kapnick cautioned against expecting the upcoming El Nino winter to be like any past El Nino winter. “No two El Ninos are alike. And the impacts of those El Ninos are not always alike,” she said.

Gottschalk said “sub-seasonal” weather patterns could preempt El Nino. The atmospheric rivers that flooded California last year occurred during a La Nina winter, which are typically dry in the southern U.S., he said.

Sub-seasonal patterns that have a stronger impact than an El Nino or a La Nina have been particularly noticeable in the western third of the U.S., he said.

“This is something that has been happening more and more in, say, the last five to 10 years,” he said.

While Oregon, Washington, Idaho and California are expected to be warmer than average, the outlook for rain and snow is more mixed.

Western Washington and most of Oregon have equal chances of average, below-average or above-average precipitation.

The odds favor a wet winter in Northern California and a dry winter in Eastern Washington and most of Idaho.

Over the entire West, drought is most prevalent in the Pacific Northwest and desert Southwest, NOAA drought forecaster Brad Pugh said.

“For both of those areas, we’re expecting drought to persist, although the drought is expected to improve along coastal areas in Washington and Oregon,” he said.

Most of the southern tier of the U.S. is expected to have above-average precipitation. Drought conditions should improve in Louisiana and Mississippi, two states suffering “exceptional” droughts, NOAA predicted.

No part of the U.S. is expected to have a colder-than-average winter.