PORTLAND, Ore. (KOIN) — With the fall season underway, you may have noticed the cooler temps, the bloom of colorful leaves, and the slight uptick in rain across the city. October is also the time of the year where meteorologists dust off their crystal balls to get a look into what may come our way this winter.
Portland is no stranger to tough winter weather. In just the last five years, the city has had its fair share of citywide snow and ice storms. In January 2024, just two winters ago, the city was blasted by a powerful ice storm for five days, causing power outages, city closures, and damage from more than 675 downed trees.
So what are the odds that this winter delivers another gut punch of power outages, school delays, or snow packed interstates?
This winter will be influenced by weak La Niña pattern, which tends to bring cooler and wetter-than-normal weather into the Pacific Northwest. It’s a setup we saw just last year. But each winter always brings its own twists and turns.
I was born and raised in the Pacific Northwest and this will be my eighth winter forecasting in Portland. Since then, I’ve collected and analyzed decades of snowfall data and trends to produce a winter report card every year. This is not my first rodeo. If you’re a numbers person, you’ll likely enjoy this article. But if not, I hope you’ll still take away the general idea of what to expect in a La Niña winter in Portland.
What is La Niña?
A key influence on how each winter unfolds is from the El Nino Southern Oscillation (ENSO). It is one of the many global climate patterns that researcher’s study.
ENSO looks closely at the relationship between changing sea surface temperatures in the eastern Pacific Ocean and its impact on the atmosphere. Each winter, we land in one of these three phases: El Niño, La Niña, or neutral. For this upcoming winter, the Pacific Northwest will enter a weak La Niña phase. Last winter, we were also in a weak La Niña.
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 to shift north and direct more storms into the northwestern parts of the U.S.
In the Pacific Northwest, La Niña conditions can lead to more active winter weather, setting the stage for citywide snow events and heavy Cascade Mountain snowpack.
Comparing La Niña Winters in Portland
First of all, check out average snow amounts in Portland across the last eight decades (1940 to 2020). You’ll notice a decreasing trend in the average amount of snowfall in Portland.
Seasonal averages in the 1950s were closer to 9.0 inches of snow per year. With our climate’s warmer trend over the last five decades, Portland’s average winter snowfall has dropped closer to 4.0 to 4.5 inches per year. Because of this, I have chosen to use data in Portland from 1970 and beyond to best model our recent snow trends in this report.
The plot below shows seasonal snowfall totals every winter in Portland since 1970. The blue dots are all La Niña winters. There have been 23 of them since 1970. The red dots are all El Niño winters and the gray 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 5.2 inches.
What also sticks out is the variation of snowfall amounts each winter since 1970. Regardless of the ENSO phase, some winters saw little to no snowfall. Some extreme winters saw 10 to 20+ inches of snow, like in 2008-2009 when 23.9 inches fell that winter.
Additionally, five of the last six consecutive La Niña winters all produced above-average — if not double the average — snow amounts in Portland. Last year’s weak La Nina winter did not fit the trend, only producing three inches of snowfall, which was below-normal.
This histogram groups snowfall events during La Niña winters into ranges.
Most of our La Niña winters in Portland (11 of them) have seen snow totals in the zero to three inch range. While La Niña is associated with above-average snowfall in Portland, many winters still experience relatively low snow accumulation. This lines up nicely with the median average for La Niña winters, which happens to be 3.0 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. We saw that just last winter. Portland collected 3.0 inches of snow, all falling in the month of February.
Beyond that, last winter was uneventful with no widescale icing events or prominent arctic blasts. While a few La Niña winters have produced extreme snowfall, most La Niña winters fall closer to or below the median average of three inches.
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 and February.
Why do we tend to see below-normal snowfall in the month of January during a La Niña winter? It’s hard to say. KOIN 6 Meteorologist, Steve Pierce, a lifelong resident of our area, theorized that if our first blast of snow-primed temperatures arrives sometime in December, it sometimes takes a month or so for the atmosphere to bring back the next round of cold and snowy weather.
“Lets say the first or second week of December we get into our first little arctic intrusion and draw the cool continental air through the gorge,” Pierce said. “I’ve noticed that snow patterns in Portland tend to take about 30 days to cycle through. So if we get a shot at snow and the right set up…it may take about 30 to 40 days to get into that cycle again.”
Of course, this is just a fun theory that’s not backed by research. It seems like every winter, we get one to maybe five moments where Portland braces for a possible snow event.
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 zero to three inch range.
- The most extreme snowfall events (10 inches or more) occur most frequently during La Niña winters.
- Portland has seen measurable snowfall for ten winters in a row. That has never happened in recorded history. We are well-overdue for snowless winter.
Given these points, I think Portland will see a winter with below-average snowfall again.
This winter will be another weak La Niña winter. Perhaps it will turn out like last year’s setup in which we saw below-average snowfall amounts and a short period of wintry weather in mid-February.
Our first cold snap could arrive in December, but it will be after the new year that we see our first chances for measurable snowfall in Portland in one or more snow events.
I would not be shocked if one of those snow storms becomes a moderate to major event, but I think we’re in for another zero to four inches of snowfall this year sometime between mid-January to mid-February. That tends to be our most active snowy window.
And as always, I put numbers to my prediction just for fun. But for what it’s worth, weather is famously unpredictable.
Anyway you put it, a dusting of snow is enough to impact the city of Portland. Please remember: This prediction is based solely on historical records, not current modeling. We will gauge the threat of snowfall as individual storms approach this winter.
Arctic Blasts & Ice Storms
I shared these stats in last year’s report and the points still stand. Last year’s winter was quite tame. We saw our coolest daytime high of 35 degrees in mid-February.
In recent years, however, our region experienced several major icing events that have been devastating with lasting impacts in our communities. The photos below are from the mid-January ice storm in 2024 that shut down the city for a week. We did not measure much snowfall that winter. It was citywide icing that brought in devastating impacts.
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.
The chart below shows the coldest daytime high temps observed during some of Portland’s most prominent arctic blasts since the 1970s.
Arctic blasts can happen during any kind of winter, often varying in scale and intensity. However, the data show that most of these prominent blasts have occurred during La Niña winters. Seven of the eight last notable arctic blasts all occurred during La Niña winters with daytime highs as cold as 25 degrees.
Mt. Hood Snowfall Outlook
La Niña winters have a noticeable impact on Cascade snowpack, delivering above-average seasonal snowfall. Here’s a chart comparing average snowfall over winter types since 1981 at Mt. Hood Meadows (elevation 5,300 feet).
The average opening date for ski season tends to fall around Thanksgiving weekend.
Even with the price of a lift ticket continuing to skyrocket, if you’re itching to buy your season pass, the odds are good for an abundant snow season in the Cascades.
Stay with the KOIN 6 Weather Team for the latest updates as the winter season approaches.
Kelley Bayern
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