PORTLAND, Ore. (KOIN) – Now that we have put a cap on our endless summer across the Pacific Northwest, let’s fast forward straight to the cold season. Imagine waking up to a white Christmas in Portland. Oh wait… We did that last year!
Unfortunately, it’s far too early to forecast snow in December or in any part of winter with any accuracy. However, we are at a point in the year where oceanic and atmospheric patterns provide signals for winter season activity, even if the snow is still a few months away.
In this article, I hope to provide insight into our upcoming winter based on historical snowfall data and current conditions. There will be lots of numbers and graphs to go over, so stick with me as best you can. My best guess for snow totals in Portland this winter can be found below. But first, we will start this analysis by looking at the Pacific Ocean.
What is La Niña?
One of the most defining characteristics of winter season activity is through the lens of the El Nino Southern Oscillation (ENSO). If you don’t know what that is, they are climate phases that the globe enters based on sea surface temperatures 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 its third-consecutive La Niña.
The La Niña phase tends to turn our weather cooler and wetter in the Pacific Northwest across the winter months. Frigid, deep ocean waters surface in the eastern Pacific and cause the polar jet stream to push north, bringing a parade of strong storms into the Pacific Northwest. La Niña winters can easily set the stage for snow events, so let’s start by taking a look at previous La Niña winters to see if there’s a trend.
Comparing La Nina Winters in Portland
Oregon Climatologist Larry W. O’Neill told KOIN 6 that he expects the forecast La Niña winter to be milder than those seen in the previous two years. This would mean a slightly colder-than-normal winter for Western Oregon, with slightly above-average rainfall and normal to slightly above-normal snowpack in the Cascades.
While scientists use trusted equipment and historical weather data to develop these predictions, O’Neill said that climate change has made annual weather forecasts less predictable in general.
“It is important to remember that these historical analogs occurred before climate change became more apparent,” he said. “Winters during recent La Niña events in the last 10 to 15 years have not been quite as cold or wet, which has led to significant year-to-year variability in the snowpack.”
Larry O’Neill makes a good point. We have seen a drastic change in the amount of snow that used to fall here in the 1950s compared to recent decades. Take a look at the graph below. Seasonal averages in the 1950s were closer to 8 to 9 inches of snow per year, versus the 4 to 5 inches of snow over the last 40 to 50 years. This is why I chose to analyze a smaller and more recent set of snow data spanning only the last 40 to 50 years here in Portland to further refine my own winter outlook.
Let’s start with a look at seasonal snowfall amounts in Portland through every winter since 1980-1981.
Average snowfall in Portland every winter is 4.2 inches. The last four La Niña winters (blue dots) have all provided above-normal snowfall amounts of 6 inches or more. There was one freak La Niña winter of 2008-2009 that brought 23.9 inches to the city – quite the impressive anomaly.
Taking into account all of our La Niña winters since 1970 (there were 16 of them) puts that average closer to 5 inches per season.
Since we will be in a La Niña phase, this data might suggest another winter with above-average snowfall.
There’s another thing to point out here and that’s the median average of 2.6 inches of snow per season. This suggests that the mean is skewed high by some of our larger and anomalous winter storms. More frequently, over 50% of the time actually, our La Niña winters have brought us only 2.6 inches of snow or less. Looking back at the plot, you can clearly see this trend between 1998-1999 to 2011-2012. Each of those La Niña winters brought about 3 inches of snow or less to the city. La Niña winters seem to either be aggressively active or somewhat tame.
Of course, any snowstorm aimed at Portland that advertises a dusting can halt the city. Even a “tame” winter will have an impact. Here are some of the odds of snowfall at PDX this winter:
- 19% chance of 10 or more inches
- 44% chance of above-normal snow amounts
- 56% chance of below-normal snow amounts
- 6% chance of trace or zero snow amounts
To gather more insight for my snow outlook, I use a method that involves “analog” years. This method takes a specific group of La Niña winters from the past that closely resembles our current ENSO pattern based on the Oceanic Nino Index (ONI). The ONI value maps the ocean temperature anomaly in a sector of the equatorial Pacific. This value classifies the strength of the ENSO pattern for that season.
An ONI index of -0.5 to -0.9 shows a weak La Niña, -1.0 to -1.4 is moderate, and -1.5 to -1.9 is a strong La Niña. This year, we are skirting along a moderate La Niña phase with an ONI index of -1.0.
You can see how the current index and forecast (dotted black lines) have a very similar trajectory to my chosen analog years.
- 2021-2022: back to back La Niña winter
- 2011-2012: back to back La Niña winter
- 2000-2001: triple La Niña winter
- 1975-1976: triple La Niña winter
- 1971-1972: back to back La Niña winter
Stacking my set of analog years with La Niña winters and the climate norms (1991-2020) shows a promising start to the winter season. Perhaps snow could be on the menu again sometime this December. On the flip side, seasonal snow across my analog years came out just 2.8 inches, fairly below average. The analog years also show quiet winter weather after the new year with very little snowfall from January and beyond.
La Niña winters tend to favor an early start to the season with near to above-average snowfall in the late winter and spring months.
Lowland Snow Outlook
In general, La Niña winters tend to bring near to above-normal snowfall in Portland with a good signature of snowfall arriving in December. Even though larger snow storms have occurred in our most recent La Niña winters, especially in January and beyond, I’m still leaning on my analog outcomes.
I predict we will see near to below-average snow amounts in Portland this winter. I bet we see one smaller snow event before the new year and little action after the new year. Any snow event in January and beyond may bring a short-lived dusting of snow across roads, maybe an inch or less, but nothing that shuts down the city like the Valentine’s Day weekend storm in February 2021. I’m calling for a tame winter ahead. And still, in the back of my mind, we are overdue for a quiet winter.
Do remember that this prediction is going off of historical records only, not actual weather model data. We will gauge the threat of snowfall as storms arrive. So take this prediction with a grain of salt.
Mountain Snowfall Outlook
Good news for skiers, snowboarders, and back-country enthusiasts. La Niña winters have historically given above-normal snowfall throughout the winter. Data provided by Mt. Hood Meadows shows seasonal snowfall since 1980 with average yearly snowfall totals around 436 inches at their base (around 5,300 feet) every season. Data is collected only when the resort is open for business from late November to May.
Some La Niña winters, like last winter, have a false or slow start with more consistent snowfall ramping up quickly after the new year. Last year brought in 499 inches for the season with an active storm cycle in January, a snow drought in February, and cold, heavy snowfall late into April and May. The past nine La Niña seasons have provided above-normal snow to the north Cascades of Oregon, some seasons providing good skiing well into springtime.
Skiing always improves as storms arrive across the region each week. We can’t see specific storms that far out. But it’s a good bet that we’ll have a healthy snowpack this year with quality skiing come January. That’s all I need to hear to get excited.
Mt. Hood Meadows has set their opening date this year to November 25, the day after Thanksgiving. I’ll see you up there!