As first seen in 5280 Magazine.

Message from Andy – I think it’s important to stress that forecasting large-scale weather phenomena like the ENSO cycle and its effects on our weather months ahead of time is not 100%. The ENSO connection to Colorado is not great and can vary widely from one corner of the state to the next. With that said, we do have info information for it to be useful in climate forecasting.

You may be aware that the planet has been experiencing a La Niña weather pattern for the past two years. That has meant differing things for Colorado: The 2020-’21 winter produced above-average snow for the Denver area—primarily due to a spring blizzard—but many mountain locations ended their seasons with snow totals below, or well below, average. Likewise, this past winter produced below-average snow totals for numerous mountain locations, most notably the San Juans.

La Niña conditions typically persist for nine to 12 months, but they can last longer. And, indeed, climatologists at the National Oceanic and Atmospheric Administration in Boulder are predicting that the current La Niña weather pattern will continue for a third year for only the third time since 1950 when researchers started keeping official records on La Niña and El Niño. Here’s what that could mean for Colorado.

First things first: What is La Niña (and El Niño)?

The La Niña weather pattern is just one part of what’s known among climatologists as the El Niño Southern Oscillation (ENSO). ENSO has three phases: Neutral is the default phase, in which temperatures in the equatorial waters of the Pacific Ocean are near normal. El Niño, “little boy” in Spanish, means there are warmer waters in the equatorial Pacific, and La Niña, or “little girl” in Spanish, means cooler waters in the equatorial Pacific.

“ENSO (El Niño/Southern Oscillation, the whole La Niña and El Niño system) has the greatest influence on weather and climate during the Northern Hemisphere cold season, so forecasters pay especially close attention when it looks like ENSO will be active in the winter.” Emily Becker says who writes the current ENSO Blogs.

How could cooler water temperatures in the Pacific Ocean affect the weather in Colorado?

The cooler waters off the western coasts of the Americas affect global weather patterns. You will often hear about how La Niña can enhance the hurricane season in the Atlantic basin. La Niña also bends the jet stream to the north in the Northern Hemisphere during the winter. This creates wet weather in the Pacific Northwest and drier weather in the southwestern part of the United States.

Deepening drought conditions, wildfires, and more severe weather, in general, are typical impacts one might see in the southwestern United States during a La Niña weather pattern. For Colorado and the surrounding region, that’s never great news—but it’s especially bad when the phenomenon lasts as long as it already has. One can easily imagine the impacts a dry and hot summer could have on the region—larger wildfires and water rationing, for starters—only to be followed by a warm, dry winter.

Why is this particular La Niña such a big deal?

Since 1950, when official record-keeping for ENSO began, there have only been two instances where a La Niña persisted for three winters in a row. The first started in the spring of 1973 and ended in the spring of 1976. The other began in the summer of 1998 and lasted till spring 2001.

This would be only the third time since Harry Truman was president that a La Niña lasted three winters in a row. This past spring, water temperatures in the Pacific not only continued to run below normal but in fact appeared to be decreasing. We’ve continued to see La Niña conditions through the summer months. La Niña doesn’t typically strengthen in the spring, leading climatologists to believe we are headed for a rare so-called “triple dip,” or a third fall and winter of La Niña conditions.

The biggest concern for those of us in Colorado would be the lack of snow this coming winter, exacerbating already distressing drought conditions in the Centennial State and the southwestern U.S. The last winters of the only two “triple-dip” La Niñas produced much less snow than normal for mountain locations. See below for map data. The winter of 1976-’77 left most mountain locations with a four- to the seven-foot deficit by the end of the season. The winter of 2001-’02 left most mountain locations with a two- to four-foot deficit. Denver had a 1- to 2-foot deficit during those two seasons.

Are there any benefits to the continued La Niña conditions?

There are: The cool waters of the Pacific tend to keep global temperatures down. That’s a good thing. As for Colorado weather, as we all know, it’s hard to predict. As we prepare for what may be a quieter winter based on forecasts, Coloradans could make a special request to Ullr, a Norse god associated with skiing and cold-weather sports, for a snowy 2022-’23 winter.

Here are some images of how the winters of the two analog years compare to normal in terms of snowfall by the end of the season. I pulled some quick data showing the last ~30 years (including 1 triple dip La Nina occurrence) and their total snow compared to normal. *Note* this is for the Denver-Central Park climate station.

Here’s the departure from mean snow and the percent of mean snow for the first Triple Dip occurrence on record back in the 70s. This is the snowfall for the season of the third year of La Niña – 1976-1977.

Lots of oranges and reds which mean deficits.

Here’s the departure from mean snow and the percent of mean snow for the second Triple Dip occurrence on record back in the early 2000s. This is the snowfall for the season of the third year of La Niña – 2001-2002.

This year also delivered less than normal snow statewide )with the exception of near Grand Junction).

We only have two analog years for Triple-Dips which is hardly enough to make forecasts off of but with all the other years in play, more times that not, La Nina is not amazing for our mountains and water supply.

~ Andy

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