One of our family friends is a brilliant oceanography professor and extremely accomplished skier, and he has a t-shirt that says “Viva La Nina.” It’s a perfect shirt for an oceanographer (since La Nina is a coupled oceanic/atmospheric phenomenon) and a Pacific Northwest skier, as La Ninas tend to bring above-average mountain snowfall to our corner of the world. We haven’t seen prodigious amounts of snow so far this year in the mountains, but beginning on Wednesday the 30th and persisting through at least the first week of January 2021, we should stay in a wet, cool pattern with tons and tons of snow in the mountains.
It isn’t a coincidence that we are ringing in 2021 with a transition to a cool, wet, and blustery pattern. La Nina’s effects on our weather are relatively subtle during November and December but usually become much more pronounced from January through March. During La Ninas, we tend to get a ridge of high pressure in the Northern Pacific and some troughing along the BC Coast south towards Northern California, and this gives us cool, moist, WNW flow – a very efficient pattern for producing heavy snow in the mountains.
Credit: NOAA
So far this winter, we have NOT seen such a pattern, despite having a moderate-to-strong La Nina in the Pacific. The bottom chart shows the 500mb height anomalies from 11/1/2020 to 12/26/2020, and you can see how there is broad ridging over the West Coast, pushing the storm track well to the north. But again, this is not particularly surprising, as La Nina’s effects on our weather often don’t become apparent until January.
However, we will see a more typical La Nina pattern to ring in 2021. A system on Wednesday will bring us an initial shot of rain and mountain snow, and another, even wetter system will swing through on Friday. Another strong system will bring heavy rain/mountain snow and blustery conditions on Saturday/Sunday, and models show several more moderate/strong systems making landfall next week!
A quick look at the “spaghetti chart” below tells you all you need to know. All those green lines mean lots of rain is expected, and with the “ensemble mean” temperature (blue) being near or below climatology (pink), this precipitation should be in the form of snow at pass level.
How much snow are we looking at over the next two weeks? Well, the “gold standard” of weather models, the European ensemble mean (i.e. the average of all the individual forecasts from the European ensemble forecasting model), is predicting 4 feet of snow at Stampede Pass (3,671′) over the next two weeks. That’s a lot for Stampede Pass. I wonder how much Mt. Baker ski resort or Paradise Ranger Station will see!
And the upper-level pattern over the next two weeks? Classic La Nina, with ridging in the North Pacific, weak troughing along the West Coast, and strong, persistent westerly flow with frequent moderate/strong storms.
Credit: StormVista Weather Models
In conclusion, enjoy the dry weather Tuesday, because it’s likely the last dry day we’ll see in some time. And if you are a skier or boarder, be sure to make the most of all the fresh snow in the mountains! Remember, you can always follow me on Facebook or Twitter for concise, real-time updates on storms as we enter this active pattern.