The back-to-back La Niña year may trigger well-paid rain, snow results

Eye on Climate

PORTLAND, Ore. (KOIN) – It was about this time last year that we all started to prepare the winter gear for the return of La Niña. The excitement was there because it was coming off a neutral year and an El Niño year before that.

La Niña is an exciting word in the Pacific Northwest (PNW) because it suggests we are in store for more mountain snow. This is the forecast that skiers and snowboarders are constantly keeping an eye out for. The storm track during a La Niña winter tends to favor more action. More action typically leads to the production of snow. Well, fast-forward to our first week of November, and here we are discussing back-to-back La Niña winters. What does this mean for you? Can we solidify a busy winter?

There have been a handful of neighboring La Niña years, some more recent than others. We can look back as early as the winter of 2016-2017, followed by 2017-2018, as adjacent La Niña seasons. You can find a list of some of the years in the graphic below. For the record, we had 11.2 inches of snow from Oct. 1, 2016 through March 31, 2017 timeframe in Portland. The next winter brought in 7.6 inches of snow for Portland. Those are two La Niña winters that brought in above average (4.3 inches 1991-2020) snowfall for Portland. That was NOT the outcome for the previous consecutive La Niña winters.

You may look at that list and assume that there have been more La Niña winters, but according to the historical data that is collected by the Climate Prediction Center, there have nearly been the same amount of El Niño years versus La Niña years (favors El Niño by 2). That doesn’t mean that we have as many back-to-back El Niño seasons. There is an excellent article from about the reasoning behind back-to-back La Niña year phases over El Niño.

Now that we have built up the base to this topic, we can look at a few graphics that are depicting the composite precipitation anomalies during a second-year La Nina winter and compare them to our long-term average from 1991-2020. According to the National Integrated Drought Information System (NIDIS) drought update, “historical composites from the seven back-to-back La Niña events on record illustrate that during a second La Niña year, the areas that benefitted the most from increased precipitation are those that are already showing some recovery from the current drought (the Pacific Northwest on the western side of the Cascades and Rocky Mountains).” 

If more precipitation is expected, then this may help with our struggling drought conditions. A topic we will explore below, keep reading! 

Based off the anomalies, that second winter of a back-to-back La Niña year may trigger more rain and mountain snow than the long-term average. It should be noted that this sort of outcome isn’t set in stone. A winter forecast is fluid! Washington State Climatologist Nick Bond agrees, he says, “what has happened more often than not in the past is not guaranteed to happen in the future, with the upcoming winter’s weather a great example.  As the season progresses, we should be able to refine how our crucial snowpack is liable to end up”.

Because of the La Niña winter coming, it is expected for above average precipitation in the Pacific Northwest (PNW) until March. You can see the sequence of 3-month maps from the CPC below. The first graphic is November, December, and January, followed by December, January, and February and finally January, February, and March. Each sequence depicts a similar forecast, which is essentially the typical outcome for a La Niña weather pattern.

If that is the case, there is a strong possibility that we can cut our drought, allowing for improvements in the PNW. The featured outlook from NIDIS, suggests the next 3 months will be enough to likely remove the drought in the northern Willamette Valley. That is represented in the graphic below by a green shade, which extends south and north into Washington. Everything in the khaki or sand color is expected to keep the drought conditions but should see an improvement. It may a pivotal time for a back-to-back La Niña to come knocking at our door, as drought conditions continue to hamper a large swath of the United States.

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