Source: maps.weatherbell.com

Big Picture

This last week, if not the whole season, has been bleak for skiers in Wyoming, Utah, and Colorado. The latest trend was a series of atmospheric rivers hitting the Pacific Northwest, at the same time that a series of clipper systems were hitting the Great Lakes and Northern Plains. This has resulted in wet, but mild, weather in the Cascades and Northern Rockies, and cold, snowy weather across the Upper Midwest. At the same time, Utah, Colorado, and most of Wyoming have been dry and much warmer than normal. The images below from the Western Regional Climate Center show temperatures last week were between 10-20°F above normal and practically no precipitation below the 40th parallel.

Source: https://wrcc.dri.edu/anom/wrcc_anom.html

Last week was a good representation of what is more likely to occur under La Niña conditions, which are present right now and for the fifth time in the last six winters. La Niña occurs when trade winds are stronger than normal, pushing warmer water west towards Asia, and forcing cold water to the surface off the coast of the U.S. and Canada. This colder sea surface creates an area of high pressure off the coast of California and/or Baja California, and forces the jet stream further north around it. This results in more storms tracking across the Northern Rockies and the Great Lakes, while the Southwestern US gets left under a ridge of high pressure.

Source: https://oceanservice.noaa.gov/facts/ninonina.html

Unfortunately for skiers in the Southern Rockies, La Niña is expected to continue for at least another month or two. According to the Climate Prediction Center, La Niña is forecast to continue into January before a return to ENSO-neutral conditions sometime between January and March. ENSO-neutral conditions generally means the Northern and Southern Rockies perform similarly, so that is a much better outcome for Utah and Colorado than what we have now.

Next Week

Thankfully, next week is a slight break from the typical La Niña pattern, as the jet stream drops a bit further south and brings some moisture, and slightly cooler temperatures, down to Wyoming and at least Northern Utah/Colorado. 

The first storm is on Wednesday, when the remnants of an atmospheric river drop down across the area. Precipitation starts near sunrise over the Tetons and far Northern Utah. Precipitation intensifies later in the morning and in the early afternoon before tapering off by the evening. Precipitation makes it to Northern Colorado in the afternoon, continues in the evening, then tapers off overnight. When precipitation starts, snow levels will be about 8,000 feet, or maybe even a touch higher. Snow levels will very slowly drop as precipitation continues, but snow levels won’t meaningfully drop until after most precipitation is done. Expect the vast majority of snow to fall above 7,500 feet, but any snow below 9,000 feet will be very dense and wet. Snow above 9,000 feet will be lighter and fluffier, and will have a much easier time stacking up.

Source: maps.weatherbell.com

The next few days will see multiple shortwave troughs bring more waves of rain/snow back to Utah and Northwest Wyoming, with very little making it over to Colorado. Snow levels will be fairly high for these storms as well, keeping accumulating snow mostly above 8,000 feet or so. The Tetons will fare quite well in this pattern, with several inches of snow every day through next Saturday.

Forecast Snow Totals Through Saturday (12/20):

Jackson Hole Mountain Resort (WY): 20″-30″

Snowbird (UT): 9″-18″

Powder Mountain (UT): 8″-15″

Deer Valley (UT): 4″-10″

Winter Park (CO): 3″-8″

Aspen Snowmass (CO): 1″-4″