WeatherWatcher: Winter Outlook

 

Snow in Lake Forest Park, February 13, 2021
Photo by Carl Dinse

I've been asked already when I expect to see our first snows this winter. It's very hard to say, but I will point out what I've been seeing with some consistency. There are a couple of sites that forecast longer range, both have been somewhat consistent with an indication of more winter type variety weather (Yes, the snow word) in the second half of December.

It’s important to remember that any of these forecasts going out beyond even a few days really start getting into the weeds of uncertainties. That is to say these forecasts start having a much higher percentage of becoming an inaccurate forecast.

Beyond a forecast, here’s my current ideas on how winter will play out for Shoreline and Lake Forest Park.

We have two main factors I generally consider. There are many more, but I like to watch the two most measured and somewhat biggest impact cycles that occur in our weather patterns. 

• The primary one that everyone talks about is the El Niño-Southern Oscillation (ENSO) cycle. This cycle is typically annual or seasonal, switching during the spring and summer months to either El Niño, La Niña, or neutral conditions.

• The second significant influence on our weather trends, particularly in the winter season, is the Pacific Decadal Oscillation (PDO). This cycle is not seasonal, or annual, but functions more on a 20-to-40-year cycle, flipping between a warm phase, and a cold phase.

So, this winter, we are in a strong El Niño, but we also have a moderate to strong cold phase PDO. This tells me that this winter isn't as likely to be the widely forecasted drier and warmer than normal winter pattern.

What does this mean for Shoreline and Lake Forest Park?

Chances of snow events will likely increase middle through late December, and I think after December our next big chances will likely be in the middle January and/or into February time frame. It could easily become another 2019 winter, where we waited until February to get all our snow. 

Our chances of a snow event for the entire winter season are slightly lower than normal, but can still happen, and can still be capable of being a large storm.

In general, I think we'll see dry stretches like the one we just finished, with stormy periods in between and heavier than normal precipitation during the active periods. We'll see if the heavier precipitation equals out the average at the end of the season or if we do end up drier, or wetter than normal.

El Niño winters with a cold phase PDO not unlike this winter that are noteworthy from Sea-Tac (unless noted):

• 1951-52: 10 inches, in December and January
• 1953-54: 23.3 inches, January, and March
• 1965-66: 22 inches, December, January, and March
• 1968-69: 67 inches, December, and January
• 2018-19: Shoreline: 20.7 inches, February, and March (snow measured in Shoreline)

There are a lot of other El Niño winters with a cold PDO phase that produced decent snow events, so in my opinion, backed up by the data I have from Sea-Tac, it is probably more likely than not that we'll see at least one or two snow events this winter season. 

They tend to show up late December, January, and February on average for this kind of set up. Other similar years have had smaller snow events, but still, multiple snow events occurred.

Seattle's record for most snow in one winter was 1968-1969 and it was an El Niño winter, with a cold phase PDO. The only other recorded winter that comes close was 1949-1950 at 64 inches of snow. Most fell in a January blizzard (Seattle’s only officially recorded blizzard). The 1949-50 winter, however, was a La Niña winter, but also with a cold phase PDO. 

For current weather conditions visit www.shorelineweather.com