Are you performing your snow dance? Putting trail maps in the freezer, turning your pajamas inside out, throwing ice cubes out the window? As we enter the new year and ski resorts start opening and churning out snow, rumblings of La Niña are circulating the ski community. This complex natural climate pattern over the Pacific Ocean leads to a strengthened ocean and wind interaction that has a ripple effect on weather all over the world. For the northwestern United States and Canada, this effect can be a colder, wetter winter. In other words: more snow. After the year we’ve had, could this be a welcome gift from Mother Nature?
In the National Oceanic and Atmospheric Administration’s (“NOAA”) November La Niña update, it was determined that La Niña is present, and has a 95% chance of continuing her reign through the winter. La Niña is a part of the El Niño-Southern Oscillation, or ENSO. It is a naturally occurring climate phenomenon that results in alternating oceanic and atmospheric conditions over the Pacific every 3 to 7 years. The perhaps more widely discussed El Niño is one phase, while La Niña is the other.
During La Niña, surface winds over the tropical Pacific are stronger than the long-term average across the basin. These strengthened easterly winds cause water to pile up over the western Pacific, which in turn allows colder water deep below the eastern Pacific to upwell off the coast of South America. Imagine if the Pacific were a giant bathtub filled with water with a fan blowing air from east to west. This breeze would slosh water across the bathtub surface, raising the water level on the west side of the tub, while the east would decrease.
The resulting effect is colder water off the coast of South America, and warmer water over the western Pacific. Warm water evaporates more readily into the atmosphere, meaning more thunderstorm activity over the region, and drier conditions over the central Pacific.
It’s unclear whether the ocean or the atmosphere initiates this process. Kind of like the age-old debate of which came first, the chicken or the egg? However, some have surmised planetary Rossby waves could be the trigger. These are large-scale waves occurring in Earth’s fluids (air and water), resulting from Earth’s rotation.
Let’s get back to the reason we’re all here: snow. For those of us in North America, the east/west ocean temperature difference resulting from La Niña causes the Asia-North Pacific jet stream to shift northwestward. This is the prevailing wind pattern high in the atmosphere that usually ushers in storm systems over the U.S. West Coast.
During the winter months of La Niña, this shift in the jet stream means the moisture and instability necessary for spectacular snowstorms are brought in over western Canada instead. This results in a wave pattern across the continental U.S. allowing cold polar air to dip south across the northern plains (much like the polar vortex we’ve heard about in the past).
The cold air and increased moisture combine to bring snow storms to the northwest. Hail to the snow gods! Of course, all of this is dependent on local weather conditions as well as topography and other features. For example, a ski resort with a higher base elevation is more likely to see big dumps from a storm during La Niña than one at a lower elevation where snow might melt on its way down.
During the last major La Niña event of 2016-2017, 4 major cities in the interior Pacific Northwest had winters within the top 5 coldest, as well as top 10 snowiest, on record. That same winter, Big Sky, Montana also had higher maximum base and peak snow depths than average. During the La Niña winter of 2010-2011, Mt. Hood in Oregon had a higher base snowfall depth than the long term historical average for 4 of the winter months.
2020’s La Niña has also been labeled as a potentially “strong” event per NOAA. This doesn’t mean we’ll necessarily see stronger storms, but it does increase the likelihood of more extreme events throughout the winter. Keep those pajamas inside out – maybe 2020 will give us something good after all.
La Niña doesn’t just bring the promise of bountiful snow across the West, it affects other regions differently. The shifted weather patterns decrease wind shear over the Atlantic. This is a primary ingredient for hurricane formation, meaning more hurricanes are likely to form during a La Niña positive year (and could be stronger, too). 2020 confirmed this by serving up a record 30 named storms in the Atlantic this season.
In the southwest, dry conditions prevail due to La Niña moving the standard moisture train northward. The current drought we’re seeing across the southwest is exacerbated by these La Niña conditions. Additionally, in a changing climate this is forecast to become even worse.
How does this affect La Niña? The story with climate change is erratic extremes. Wetter areas will get wetter, while drier areas get drier. This means as hurricanes grow stronger in a warmer world, areas already prone to drought such as the southwest will get even drier. Not to rain on your parade (or cancel your pow day), but this does not necessarily mean future La Niña positive years will bring even bigger snow dumps.
La Niña is overall an exchange of heat between the ocean and atmosphere. It is not creating or taking away heat out of thin air (pun intended). There are many moving parts and phenomena that affect ENSO, and climate scientists aren’t exactly sure how it will be affected with climate change. It is surmised that the impacts of ENSO (like the weather patterns mentioned above) will be affected, and therefore the likelihood of extreme events.
You’re now well equipped to understand the Snow Goddess La Niña since we’ll all be subject to her rule this winter. Continue to perform your snow dance and crank out those early season lunges as we prep for a winter on the slopes that is hopefully snowier, and safer, for all of us. 2020 owes it to us after all.