What does El Niño mean for the coming winter in the Portland region?
PORTLAND, Ore. (KOIN) – Make some room for the chill of winter. The cold season is coming and will arrive faster than we know it.
Could this winter bring us another citywide snowstorm? The meteorologist in me says, "BRING IT ON!" and the rational, working, adult human in me says, "no, thanks..."
In recent years, our region has gotten a mess of impressive snowstorms over the winter. We all remember the one back in February this year, when a record 10.8 inches of snow fell over Portland and shut down the city. Check out some photos from the storm below.
If you have any real trauma in place from last year's snow crisis, you may be in luck. This winter, we have an El Niño climate pattern in place, which can bring in warmer and drier weather into the Pacific Northwest over the winter months.
Read along as I dive into Portland's historical weather data and climate indicators, like the El Niño Southern Oscillation, to give insight into what we can expect as winter approaches. I hope to dive into three main areas for you:
- What is El Niño and why everyone talks about it
- How El Niño winters impact Pacific Northwest weather and how they compare to normal winters
- The snowfall outlook in Portland - what our winter weather may look like in the coming months
El Niño Explained
First of all, what is El Niño or La Niña? They get brought up every year... and that’s because they can affect the weather worldwide, especially during the winter months.
During an El Niño pattern, warmer-than-normal ocean water in the Pacific pools up along the equator in the eastern parts of the Pacific ocean. This causes the jet stream, or the storm track, to dive south, causing wetter and stormier weather across portions of the southern U.S.
In the Pacific Northwest, El Niño conditions tend to lead to warmer & drier winter weather. With the jet stream directed south of our region, that can translate to fewer storms marching into the region, and a quieter pattern across the winter months. Fewer storms could result in less rainfall, which may lead to less opportunity for citywide snowfall.
To get a better idea of El Niño impacts, lets take a look back at previous El Niño winters in Portland to see if there is a below-normal snow trend.
Comparing El Niño Winters in Portland
First of all, it is easy to see the drastic decrease in seasonal snowfall in Portland across the decades. Seasonal averages in the 1950s were close to 9" of snow falling every winter in Portland, and dropped to 4-5" per winter from the 1970s to now. I chose to analyze only the El Niño winters after the 1970s, since they provide a better representation of snowfall received in Portland these days.
The chart below shows seasonal snowfall amounts in Portland since the winter of 1980-1981 to last year. The red dots indicate El Niño winters and there have been 13 of them since 1980.
Normal snowfall in Portland every winter is 4.2 inches. This value is based off the last three full decades. In this case, “normal” means the 30-year average from 1991-2020.
Our last El Niño occurred during the winter of 2018-2019, when Portland received 7" of snowfall. It was an impressive, above-normal amount for the season. However, the six El Niño winters prior to that year each brought well below-normal snow to the city.
Taking into account all of our El Niño winters since 1970 (there were 18 of them) puts that average closer to 3.2" per season.
Here is another way to look at the data. Below is a histogram of El Niño winters since the 1970s. This graph shows the distribution of El Niño winters based on how much snow fell that winter. For example, seven El Niño winters brought 0" to trace amounts of snowfall to Portland. Three El Niño winters brought 3-4" of snowfall to the city... and so on.
More often than not, El Niño winters skew towards the lighter, below-normal side of snowfall. The median average also dropped that amount to just 2" of snowfall during El Niño winters. (This suggests that the mean average is skewed high by several anomalous winter storms, like the winter we received 12-13" of snow.)
Looking back at the histogram, you can clearly see this trend. The majority of El Niño winters produce 2-3" of snowfall or less.
Of course, any snow storm aimed at Portland that advertises a dusting can halt the city. Even a “tame” winter will have impact. Here are some of the odds of snowfall at PDX this winter:
- 6% chance of 10 or more inches
- 33% chance of above-normal snow amounts
- 77% chance of below-normal snow amounts
- 39% chance of trace or zero snow amounts
Impacts of a "strong" El Niño
A “strong” El Niño is also forecast this winter. Does the intensity of an El Niño influence the amount of snowfall we see during the winter?
Our last strong El Niño occurred in 2015-2016 when 1.4" of snow fell. And before that, the strong El Niño of 1997-1998 brought 8.7" of snow to Portland. The numbers are all over the place...
Take a look at the graph below comparing all El Niño winters and the six strong El Niño winters that have occurred since 1970. There doesn’t seem to be any major influence based off of the intensity of an El Niño. Average snow amounts are still below what's normal for a winter in Portland.
Snowfall by the Month
El Niño winters may also favor an early start to the season. Records show above-normal snowfall across the month of November, which is normally a month that we don't receive any snowfall at all.
December and February also see lower snowfall amounts during El Niño winters. January has relatively similar snowfall in both normal and El Niño winters, with only a small difference.
Snow Outlook - What could we see this winter?
El Niño winters tend to bring in below-normal snowfall to Portland with an early start to the season - so that's what I predict this winter.
Perhaps we see our first winter weather threat in November with a quick dusting down to the valley floor. Just trace amounts, nothing measurable. Then the rest of the winter is pretty quiet.
If I had to paint the winter picture, I see plenty of chilly, dry, and cloudy days. Expect daytime highs in the 40s and overnight lows in the 30s. Expect foggy mornings and inversions. That means the valley gets stuck under a dense blanket of fog and low clouds, and the mountains and coastline shine under the sun. We could get stretches of dry days, where we may see a week or more with no rainfall.
Here's my prediction for snowfall each month this winter:
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. Take this prediction with a grain of salt.