PORTLAND, Ore. — The National Oceanic and Atmospheric Administration's Climate Prediction Center is predicting a weak La Niña will emerge this fall and will persist through the winter.
La Niña winters for Portland statistically favor cooler than normal temperatures with a good Cascade snowpack and near normal to above valley rainfall.
The flow pattern is typically active with the jet stream entering the Pacific Northwest, bringing a high number of weather systems delivering precipitation.
This winter's ENSO Cycle favors a developing La Niña, but leaves the door open for a neutral pattern. Notice strong and moderate La Niña winters favor above normal rainy season precipitation totals for Portland, but a weak La Niña favors a drier than normal period.
A La Niña winter season brings good news for the Mount Hood and Cascades snowpack. La Niña seasons heavily favor near normal to above mountain snow and are often the snowiest winter periods for higher elevations of the Northwest.
Valley temperatures, specifically Portland, average below normal temperatures for La Niña winters. One of the main reasons to expect cooler than normal temperatures with a La Niña is a heightened chance of seeing an Arctic blast. With an increased chance of seeing a prolonged period of freezing weather comes an increased chance of snowstorms dumping eight inches or more over the city. La Niña winters typically see more valley snow than ice which would be the opposite of last winter.
The conclusion is that La Niña winters most often produce a good snowpack in the mountains and colder than normal temperatures in the valley. Valley precipitation totals decrease with a weak La Niña and increase with a stronger La Niña. Valley snowfall chances are elevated, including the chance of a major snow event.
Recent La Niña seasons include:
- 2008: December saw 19 inches of snow and had a record depth of 10 inches of snow on the ground Christmas Day.
- 2017: January had 6.5 inches of snow in Portland and 15 inches in the West Hills at Pittock Mansion.
- 2021: February had 10 inches of snow in Portland.
