Can you guess Portland’s average first snow date?

Eye on Climate

A car sits in a ditch along a snowy road in the Portland metro, Feb. 11, 2021. (KOIN)

PORTLAND, Ore. (KOIN) – We know that winter is just about here, but that doesn’t mean the valley snow is. Snowflakes flying in the sky can cause quite the excitement, especially if it’s the first snow of the season. When does that typically happen?

If you’ve been around long enough, you know that some winters in Portland we don’t even have measurable snow. Portland is not on the same playing field as Mt. Hood and the lovely Cascade mountain range. So you may be thinking back to recent years, and if that is the case, well you may have come up with a response that was focused around February. Believe it or not, in the last three snow seasons, Portland hasn’t experienced our first snowfall until February and March. This is a snow event that is more that is 0.1 inches or greater.

Are we just a post-New Year snow city? Well, that’s not always the case! In fact, we’ve had a few early December snow events just going back through the previous nine snow seasons. You can see the list below, which is the date and amount of the first snowfall of the season. Yikes, both 2012-2013 and 2014-2015 were seasons that didn’t bring in any measurable snow. It’s not unheard of, but it does feel like you’re missing out on the true glory of the winter season. What I find interesting, is the first snow event tends to be light, or it is just a small fraction of a larger multi-day event. For example, we collected over 10 inches of snow through the stretch of February 11 to February 14 last winter. However, the official first snow on February 11 was 0.1 inches, just the very start to a winter storm.

Using data that has been collected by the National Weather Service in Portland, we have a general idea of the average first snow date. This is an event that is equal to or greater than 0.1 inches of snow. That average first snow date turns out to be near the end of December, coming in at December 26. Of course, there are years that we have snow earlier, or later, but this is the average across that wide timespan. Does that seem correct to you? The earliest first snowfall on record is November 11, 1955. Once again, keep in mind, this is a measurable snow event of 0.1 inches or greater. We aren’t talking about a mix of rain and snow coming to the ground.

How does that stack up over a 30-year average separated into six groups? It’s very similar, with the average first snow coming in around the last week and a half of December. The earliest seemed to be in the 30-year span of 1970-2000, with the average first snow coming in at December 23. Both the 1940-1970 and 1990-2020 range share a date of December 31. Does this mean our chance for snow on Christmas and New Years Eve is high? This doesn’t guarantee either, and if you’re interested, it’s around a 1% chance for a white Christmas Day. If you reference the list above, you will notice that there is a December 24 snowfall!

If there is ever a competition for when we may see the first snowfall in Portland, you may want to place your odds somewhere in the last week of December. I would just avoid December 25.

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