Portland’s 2024-25 Winter Weather Outlook

PORTLAND, Ore. ( KOIN ) —  With a chill finally back in the air in Portland, it’s starting to feel a little more like fall. The rain will start to pour, temperatures will continue to drop, and darkness will soon arrive before 5 p.m. Before we know it, the winter season will be here with the chances for snow and ice knocking on our door.

This winter, we have a weak La Niña climate pattern in place, which tends to influence a cooler and wetter-than-normal weather pattern in the Pacific Northwest over the winter months. That may sound like horrible news, especially after last season’s major ice storm that wreaked havoc across Northern Oregon and the Portland metro area. That storm brought $72 million in damage across 16 counties here in Oregon and Southwest Washington during Jan. 13-17, 2024.

So what are the chances that something like that happens again? Read along as I dive into Portland’s historical weather data and climate influencers, like La Niña, to give you insight into what conditions we can expect this winter. Your eyeballs may hurt while reading this. There are a lot of numbers and charts in this article. So, please bear with me! My hope is to enlighten you with statistics and help you understand the likelihood of another snowstorm in Portland.

What is La Niña?

One of the most influential characteristics of an upcoming winter season is the El Niño Southern Oscillation or “ENSO” for short. ENSO is a large-scale climate phase that the globe enters based off of sea surface temperatures observed in the Pacific Ocean. Each winter, we are in one of these three phases: El Niño, La Niña, or neutral. This winter, the Pacific Northwest will enter a weak La Niña pattern, coming off of last winter’s very strong El Niño.

During a La Niña pattern, cold ocean water is upwelled in the Pacific Ocean and starts to pool up along the equator in the eastern parts. This causes the Polar jet stream, or the storm track, to shift north and direct more storms into the northwestern parts of the U.S.

In the Pacific Northwest, La Niña conditions tend to lead to more active winter weather and can easily set the stage for snow events. Let’s take a look at previous La Niña winters to see what trends we can find.

Comparing La Niña Winters in Portland

First of all, I like sharing this chart because it shows the decrease in seasonal snowfall in Portland across the decades. Seasonal averages in the 1950s were closer to 9 inches of snow per year. This was likely the case when temperatures on average got colder, and stayed colder. However, over the last five decades, Portland’s average winter snowfall has moved closer to 4 to 5 inches. In my analysis, you’ll notice that I have chosen to use data in Portland from 1970 and beyond for consistency.

The plot below shows seasonal snowfall amounts every winter in Portland since 1970. The blue dots are all La Niña winters – there have been 22 of them since 1970. The red dots are all El Niño winters and the black dots are neutral winters.

The average snowfall in Portland across all winters since 1970 is 4.5 inches. You’ll notice how the average snowfall in Portland across La Niña winters is greater , at 5.3 inches. And the average snowfall in Portland across El Niño winters is much lower than average at 3.2 inches.

What also sticks out is the variation of snowfall amounts each winter since 1970. Some winters saw little to no snowfall as well as some extreme cases seeing 10 to 20 inches of snow, like in 2008-2009, when 23.9 inches fell that winter. Also, the last five consecutive La Niña winters all produced above-average, if not double the average snow amounts in Portland.

Here’s another way to look at the data. This histogram groups snowfall events during La Niña winters into ranges.

What’s noticeable here is that most of our La Niña winters tend to fall in the 0 to 3 inch range. This indicates that while La Niña is associated with above-average snowfall in Portland, many winters still experience relatively low snow. This lines up nicely with the median average for La Niña winters, which happens to be 3 inches. That shows that while some winters can produce extreme snowfall, most winters fall closer to or below the median average of 3 inches.

This also suggests that the data is skewed by some of our most extreme snow events, like February 2023’s “Snow-pocalypse” that brought a record 10.8 inches of snow to Portland, the second-largest single-day snowstorm in recorded history.

These outlier events raise the average, making La Niña winters appear snowier overall. But many La Niña winters can actually be quite tame!

On the flip side, El Niño winters often produce below-normal snowfall amounts in Portland. For example, last year was icy, but we only received 1.6 inches of snow throughout the winter. And seven of the last eight El Niño winters since 2000 have also brought in below-normal or zero snow to the city.

Looking at snow data on a monthly basis, La Niña winters tend to bring near or above-average snowfall in the peak winter months of December through February. Notice the above-average snowfall in the month of December. Perhaps we’ll see an early start to the snow season with a wintry storm near the holidays? February is also a standout with a noticeable increase in above-average snow during La Niña winters.

My Portland Snow Outlook

So, what can we conclude from all this data? Here are the main takeaways:

• La Niña winters are associated with above-average snowfall in Portland.

• The majority of La Niña winters since 1970 have produced snow events in the 0 to 3 inch range.

• The most extreme snowfall events (10 inches or more) occur most frequently during La Niña winters.

I hate to say it, but given these trends, I think it’s very reasonable to predict another winter in Portland with above-average snowfall .

Every winter, we usually receive all of our snowfall within three to five storm systems, or events that are cold enough to bring snow down to the valley floor. This year, I bet we see one small snow event before the new year that drops a dusting to an inch of snow. Then, after the new year, we could see one to three more events between mid-January to late February . Maybe one of those is a moderate to major event.

If I had to put numbers to my prediction, this is my guess. And let me be clear, I really hope this does not come true!

Anyway you put it, a dusting of snow is enough to impact the city. Please remember, this prediction is based solely on historical records , not actual weather data and observations or current modeling. We will gauge the threat of snowfall as individual storms approach this winter.

Arctic Blasts & Ice Storms

When it comes to winter, our city is no stranger to the snow. In recent years, our region has experienced several major icing events that have been devastating, with lasting impacts in our communities.

Snow or ice storms in Portland usually start the same way, with a frigid airmass dropping out of Canada. This arctic air slides its way south through eastern Washington and Oregon and rushes through the Columbia River Gorge into Portland. Once this dry and dense airmass arrives, it pools into the valley. We tend to see daytime high temps in Portland falling into the 20s, sometimes sitting below-freezing for days at a time. This is what we call an arctic blast.

This chart below shows the coldest daytime high temps observed during some of Portland’s most prominent arctic blasts since the 1970s.

The data shows that, although arctic blasts can happen during any kind of winter, most of these prominent blasts have occurred during La Niña winters. In recent winters, we’ve seen daytime highs as cold as 25 degrees. The all-time coldest days on record at the Portland International Airport (period of record 1940-2024) was from the arctic blasts of December of 1968, when Portland hit only 14 degrees for a daytime high and then again in February 1989, when Portland only reached a high of 15 degrees. Brrrrr!

Our KOIN 6 meteorologist Steve Pierce , has lived through decades of Pacific Northwest winter storms and I love picking his brain when it comes to our winter synoptics. Here’s what he had to say about the set up of ice storms in Portland:

“After a few days of below freezing temperatures in the valley, the cold arctic air will slowly erode from the top down by a much warmer pacific frontal system riding in from the ocean. The warmer air is forced up and over the colder arctic dense air that sits on the surface in the valley. As the water droplets fall into the shallow cold layer near the surface, the water droplet does not have enough time to reform into an ice crystal (snowflake). In this case, the water droplet is super-cooled and freezes on contact with the surface. That is the classic set up for an ice storm. There are many of these events that have been well-documented over the decades in the Portland area and there will be more to come.”

Mt. Hood Snowfall Outlook

Last but not least, let’s talk about mountain snowfall in La Niña winters. As an avid skier and snow-shoer, I love keeping an eye on our snowpack well into the spring season. Snowpack in the west is so important. It’s not only needed for winter recreation, but for nature’s ecosystems and water supply in the drier months, helping to fill up reservoirs in many states.

Thankfully, La Niña winters tend to provide the powdery goods with above-average seasonal snowfall. Here’s a chart comparing average snowfall over winter types since 1981 at Mt. Hood Meadows (elevation 5,300 feet).

El Niño winters tend to provide below-normal seasonal snowfall. However, that is not always the case. Last winter was an El Niño, and the Mt. Hood Meadows team was happy to report that the resort received 479 inches, which was more than 3 feet over the seasonal average and one of the highest totals for an El Niño season on record.

The average opening date for ski season tends to fall around Thanksgiving weekend. With a La Niña winter in store, we may be able to ski off the turkey this year. The odds are good for an abundant snow season in the Cascades!

For the latest news, weather, sports, and streaming video, head to KOIN.com.