If you’re anything like us, ski season is always on the brain and nothing gets the snowy synapses firing quite like a long term winter forecast from our friends over at NOAA.
According to a recent report from NOAA’s Climate Prediction Center, there is a 50-55% chance of La Niña conditions arriving this fall and lasting throughout the winter of 2020-2021.
What does a La Niña winter mean?
On a typical La Niña year, the jet stream tends to have a more northern positioning, which can mean consistent cold storms in places like British Columbia, Oregon, Idaho, Wyoming, Montana, Utah, and central/northern Colorado.
While each La Niña has the potential to be wildly different than the last, the southern states of the west tend to get slightly less than average snowfall. That said, the last La Nina delivered historic snowfall to the California, so take these generalizations lightly. But on the whole, the northern mountains of the Western United States are generally favored by a La Niña pattern in terms of snowfall and temperature.
What causes El Niño and La Niña?
Good question. Perhaps one of the more complicated climate interfaces in our natural world, the El Niño Southern Oscillation (ENSO) is responsible for wide ranging shifts in weather patterns that is caused largely by the heat content and positioning in the Pacific Ocean.
“ENSO is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe” – NOAA
Depending on the temperature of the western vs. eastern regions of the equatorial Pacific Ocean, the atmosphere and subsequent meteorological drivers like the Jet Stream can be altered and have wide ranging effects on everything from rice harvests in Indonesia to snow depths in Colorado. On a typical La Niña year, the heat content in the south eastern Pacific is below average, which in turn causes the jet stream to move further north and subsequently, delivers more snow and cold temperatures to the upper half of the Western United States.
So what about this winter?
Like with all things weather, forecasting beyond 10 days is extremely difficult. While long term modeling has come a long way in the last decade, these predictions should not serve as an accurate representation as to whether or not there will be powder for you Christmas vacation in Big Sky. So stay flexible getting your snow dance on, because after all, it never hurts to dance.
NOAA Precipitation Outlook – Winter 2020-2021
NOAA is predicting above average snowfall this winter in Montana, Wyoming, and the Great Lakes area with an increased chance of precipitation in Northern Colorado starting in March. Equal Chances (EC) for average snowfall exist in most of Colorado, Utah, California, Nevada, Idaho, and the Pacific Northwest. Those that could be hurt by the La Niña pattern include Arizona and New Mexico.
November – December
January – February
March – April
NOAA Temperature Outlook – Winter 2020-2021
The unfortunate news is that NOAA is projecting above average temperatures for most of the United States throughout the winter of 2020-2021. However, a chance for colder than normal temperatures could show up in the spring according to Climate Prediction Center models. Also, if La Niña shows up in force, expect these temperature outlooks to change drastically, with an opportunity for cold temps to cover the northern and central portions of the Rocky Mountains.
November – December
January – February
March – April
La Niña Watch | NOAA
ENSO-neutral is favored to continue through the summer, with a 50-55% chance of La Niña development during Northern Hemisphere fall 2020 and continuing through winter 2020-21 (~50% chance).
During June 2020, sea surface temperatures (SST) were near average in the east-central equatorial Pacific and below average in the eastern Pacific. The Niño-4 and Niño-3.4 indices were near zero during the latest week, while the Niño-3 and Niño-1+2 indices were negative. Negative equatorial subsurface temperature anomalies (averaged across 180°-100°W) weakened from May through June. However, below-average subsurface temperatures continued in the eastern equatorial Pacific. Also during the month, low-level wind anomalies were easterly across the east-central Pacific, while upper-level wind anomalies were westerly over parts of the far western and eastern Pacific. Tropical convection was suppressed over the western and central Pacific, and near average over Indonesia. Overall, the combined oceanic and atmospheric system is consistent with ENSO-neutral.
The models in the IRI/CPC plume are roughly split between La Niña and ENSO-neutral (Nino-3.4 index between -0.5°C and +0.5°C) during the fall and winter. Based largely on dynamical model guidance, the forecaster consensus slightly favors La Niña development during the August-October season, and then lasting through the remainder of 2020. In summary, ENSO-neutral is favored to continue through the summer, with a 50-55% chance of La Niña development during Northern Hemisphere fall 2020 and continuing through winter 2020-21 (~50% chance; click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).