Another winter expected to be under the spell of La Niña

Eye on Climate

PORTLAND, Ore. (KOIN) – Depending on your stance about winter, you may be rooting for one El Niño-Southern Oscillation (ENSO) phase versus another phase.

You may be a fan of El Niño or you may be a fan of La Niña for the winter months. Why? You may have learned over the years that one may mean more snow and rain and the other may lead to less snow.

Around the Pacific Northwest (PNW), when you’re a fan of snow, you usually listen for the key phrase of “it’s going to be a La Niña winter”. If you’re just learning about these terms, you can learn all about ENSO in a KOIN weather explainer article here.

As you gathered from the title, we are anticipating back-to-back winter seasons in the La Niña ENSO phase. This is cooler than average sea surface temperatures, which more often than not impacts the weather pattern globally. The development of storms and the tracking of the jet stream are typically altered from what may happen during an El Niño winter. We will just focus on what occurs during a La Niña year and what it means for Portland (and the mountain).

You can find a loop of the general La Niña setup below.

For the PNW, conditions tend to favor more rain and potential snow for the valley. This usually translates for the mountains as well, but we will discuss that in more detail below. I mentioned that the jet stream plays a factor by offering a storm track that is more often than not busy for Washington and Oregon. You can see in the graphic below that it slices straight across the PNW and down to the southeast. This is generally the track of cool and wet systems that pass by our neighborhood. The cold air from the north isn’t very far away, which allows for the mountains and the eastern sides of the state to borrow some of that cold air if the jet meanders in our direction. Once that cold air finds a way to the Columbia Basin, it just takes a shift in the wind for it to get directed towards the Willamette Valley. It’s that formula that leads to the snowfall in Portland and the valley floor (more often than not).

WHO IS READY FOR SNOW AND RAIN?

With the anticipation of another La Niña winter, we should look at the rain and snow outcomes in Portland when we’ve had a La Niña favored winter. Will it look like the photo next to us? Which one do you prefer? We’ve had some rainy years and we’ve also had some years where the snow has come down.

Before we tackle those numbers, I do want to note that each phase has different grades of strength. Just how cool or warm is the water. It is possible that some La Niña years are closer to a neutral year than others. You will notice in the lists below that we have put the phase strength next to the year. It ranges from weak, moderate, and strong.

The evidence for more snow or rain based on the sea surface temperature anomaly level will not be explored in this article.

Recent La Niña years have a range of 19.52 inches of rain in Portland (airport) to 33.24 inches of rain. That is through the window of November 1 to April 1. This is the period of time was used because that tends to be the months that Portland has seen measurable snow (although snow has fallen before in April). The average rainfall in Portland through the five most recent La Niña winters comes out to 26.55 inches of rain.

Right now, there is a 57% chance this will be a moderate La Nina and only 15% that it will be strong, said Mike Halpert, deputy director of NOAA’s Climate Prediction Center. 

As far as snow goes? If we take the same five La Niña winters, the range goes from 1.8 inches of snow to 11.2 inches. The year that provided the most rain, produced the most snow. That being said, it’s likely just happenstance. The next wettest season produced the lowest amount of snow in a strong La Niña in 2010-2011. The purpose of this article is to show the variety from one La Niña winter to the next. The average snowfall over those five years comes out to 6.7 inches of snow.

What is typically more of a talker at this time of the season is the snowfall for the mountains. If you were thinking about jumping on a pass from a local ski resort, they say these are the best years to do it. The snow total average at Mt. Hood Meadows from 1980 to 2019, shows that there is an edge in the La Niña winters compared to others. Get the skis and the snowboards ready, because if there is one thing that we do know, the mountain is always fun time.

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