With the days rapidly getting shorter and the first major system of autumn only hours away, I’ve been getting more and more excited for the beginning of storm season. There’s nothing I love more than a good Pacific Northwest lowland snowstorm, and windstorms, mountain snow, and heavy rain aren’t far behind.
So when I caught wind Thursday evening that the Climate Prediction Center had issued a La Nina watch, I was naturally happy to hear the news. La Ninas tend to bring us cooler and wetter-than-normal winters, with significantly more snow in the mountains and a greater-than-normal chance of snow in the lowlands.
According to the Climate Prediction Center’s latest El Nino/Southern Oscillation (ENSO) Diagnostic Discussion, sea-surface temperatures in the central and eastern Equatorial Pacific have decreased from slightly above-average to slightly below-average over the past couple months.
Credit: Climate Prediction Center/NOAA
Additionally, both low-level and upper-level trade winds are above average (albeit in different places), convection is enhanced over Indonesia and suppressed over the central/western tropical Pacific, and ocean temperatures have decreased below the surface. These are all things we’d expect as we transition into a La Nina in the Tropical Pacific.
Credit: Climate Prediction Center/NOAA
Models are split on whether our current pattern (which, while showing La Nina characteristics, is not strong enough to be considered a La Nina) will transition into a full-fledged La Nina over the next several months. The statistical and dynamical models from Columbia University’s International Research Institute for Climate and Society show us remaining in ENSO-neutral conditions for the winter, while most models/ensemble members from the North American Multi-Model Ensemble show us transitioning to La Nina conditions in the next couple months
Credit: Columbia University/CPC
Because the atmosphere is currently in and continues to trend toward a La Nina pattern, forecasters give a 55-65% chance of La Nina forming during the winter compared to a 35-45% chance for Neutral conditions. If I had to guess, I’d say our most likely outcome for this winter is a weak La Nina developing in October/November and persisting through February.
La Ninas are known for bringing cooler and wetter-than-average winters to the Pacific Northwest, giving us above-average mountain snowfal. This is due to the tendency for a large ridge of high pressure to form in the NE Pacific, pushing the jet stream north into Alaska where it can tap into a cooler air mass before coming back over the ocean and sending storms into the area.
Credit: Climate Prediction Center
That being said, there is more year-to-year variability during weak La Nina (and El Nino) years than strong ones. So while the chances are in our favor for a snowier-than-average winter in the mountains, I wouldn’t go placing any bets on it.
As previously mentioned, La Ninas also give us a greater chance of lowland snowfall! They are far better than El Nino years, which squash the hopes and dreams of schoolchildren everywhere.
Credit: Nick Bond, retrieved from Scott Sistek’s 2016 Winter Forecast Blog Post
Sizable (though not record-breaking) flooding is also more frequent during La Nina years, as are strong windstorms. Our very strongest windstorms have all occurred during neutral years, however.
It’s worth mentioning that last year was also a weak La Nina, and last winter was pretty darn epic (particularly in the snow, freezing rain, and forecast bust departments). If this winter is even half as exciting as last winter, consider me satisfied. But there’s nothing I’d love more than for the winter of 2017-2018 to put last year’s winter to shame.
Finally, if you want a more in-depth explanation of how La Nina and its brother El Nino work, click here. I can’t think of any feature that has a larger impact on weather not just in the Pacific Northwest, but across the entire world.
Have a great Sunday!
Charlie
4 Comments
Great write-up, Charlie! I’m more familiar with La Niña/El Nino effects on the East Coast and California. Good to know that chances are better for snowfall here in the PNW during La Ninas! My snow board is ready to go. I received 16.0″ here last year, mostly from the surprise 10-incher in January. We live on a long, steep hill at 600′ and I got home just in time at the start of that storm as the roads were getting quite slippery. I was able to enjoy it all from the comfort of home compared to my 7-hour drive home from work during the smaller December snowfall – ugh! #notenoughsnowremovalequipment, #nosaltallowed.
I’m so ready for the shift in weather. Hoping we get a la Nina winter! Great post.
Super post. Lots of information. Me, as much as I hate winter, I’m hoping for a no on the full-blown la Nina….but like everyone else, I get what I get. Thanks again, for the info.
Patricia, you deal with MUCH harsher winters in Michigan than we do in Portland, so I completely understand! For us, La Ninas just mean 44 degrees and rainy instead of 45 degrees and rainy, and there’s nothing skiers love more than low snow levels 🙂
Thank you Laura and Jeff! I am definitely looking forward to the shift too. They’ll allow salt on the roads this year, but I don’t think it helped with the surprise January snowstorm – there’s not much you can do once the snow has already compacted onto the ground.