Salem had a toasty high of 85° today!! The next several days are going to be much warmer than normal with highs in the mid 80s as we end September and begin October. I imagine everyone will be doing their best to enjoy the nice weather because we all know our wet season is just around the corner…

Since fall is here, even if it doesn’t totally feel like it, I figured it could be both fun and a good time to share a few thoughts on this upcoming winter. I’ve never done something quite like this before and to be honest some years, like last year, are more of a crapshoot; however, this year we are expecting a moderate La Nina which gives us a few extra hints as to what type of weather we are likely to see this winter.

For this discussion I analyzed 11 La Nina winters which had similar strength to the one being predicted this year. I’ll also be referring to the months of November through March which I consider to be our primary storm/winter season. There are some years where the storm season really gets going during mid October, and this could be one of those years, but the statistics I looked at and the focus of this discussion are centered on the months of Nov – Mar. This first chart shows those 11 La Nina winters and how they fared in terms of precipitation for Salem, whether or not there was a valley flooding event, and Salem’s total snowfall in inches during each of those winters.

1.) Perhaps the number one thing that stands out is how wet La Nina winters typically are in the valley. 9 of the 11 La Ninas surveyed gave Salem above normal precip. That lends pretty solid confidence we will end up wetter than normal. As is the case every winter, Salem should still see a number of dry days mixed in. The key thing to remember is that overall statistics favor a wetter and rainier than normal winter for the Willamette Valley.

2.) Not shown on the chart, but odds also favor an above normal or at “worse” an average mountain snowpack this year which is great news for skiers/snowboarders and our water supply. One caveat is there have been a few La Nina winters which got off to a slow start in the snow department meaning Nov and Dec weren’t necessarily real good in terms of mountain snow; however, the vast majority of those winters still saw an excellent second half to the ski season as snow ramped up nicely in Jan and Feb of those years.

3.) This next one is not good news. Keep in mind I’m strictly talking odds here by looking at what happened in past La Ninas, but for this one the odds are not in our favor. Of the 11 years surveyed, 8 saw a notable (either minor or major) valley flooding event. The percentage of La Nina years with significant flooding events is high when compared to non La Nina winters. Below is a list of historic flood events on the Willamette River in Salem. This list only contains floods occurring since flood control dams were built in the 50s. It’s no coincidence that 10 of Salem’s 13 worse floods occurred in La Nina winters, and while it’s far from certain, one would be wise to keep this in the back of their mind, especially if you live in a flood or mudslide prone region as the odds of seeing some sort of flooding event this year are higher than normal….

4.) Perhaps the most anticipated question is whether or not it’s going to snow here in the valley. Well, 11 of the 11 La Nina winters I reviewed in detail produced at least some snow here in Salem. Woo hoo! Breaking it down further, 6 of those years produced enough snow for sledding or building a snowman in (highlighted in purple on the chart). The other 5 only saw minor accumulations of a slushy inch or two. Take it for what you want, but odds are high we at least get an inch or so of snow, and odds are higher than normal we see a respectable/decent snowstorm at some point this winter. Far from a slam dunk as I like to say, and we are talking statistics, but it does provide some extra hope for us snow lovers. Definitely better odds than last winter! 🙂

So yes, may the odds be ever in our favor, and with how 2020 has gone I really do mean that. A quick recap for you:

1.) Odds favor a wetter/stormier than normal winter overall.

2.) Odds favor a good mountain snowpack and good year for ski resorts.

3.) Increased odds for a significant valley flooding event.

4.) Higher than normal odds for some valley snow.

For reference, here are all La Nina winters (regardless of their strength) since 1960. Again, the pattern is the same. Almost all of them ended up wetter than normal, many of the years had flooding here in the valley, the majority of these years had a good mountain snowpack, and all of them produced at least some measurable snow (albeit some years it was no more than an inch or two) down to the valley floor.

The odds definitely favor a more active winter, but only time will tell, so be ready for anything, and then I guess just sit back and see what happens…