December marks the start of meteorological winter — when temperatures plunge, heavy coats are in fashion and kids begin picking their teams for snowball fights.
So what have we seen this year? Unfortunately, not much.
The lackluster snowpack is particularly worrisome amid widespread drought in the region — 94 percent of the West is experiencing drought, and many lakes and reservoirs are at historically low levels. A healthy snowpack this winter could help replenish water levels during the spring melt season -— but if snowpack is limited, deficits will grow.
Warm and dry conditions this fall have led to significant snowfall deficits across the western United States. November was warmer than average, and precipitation was below average everywhere except Washington state, which had a string of storms that caused major flooding.
November 2021 really put the "no" in snow, with a majority of the country seeing below average snowfall last month. The only exceptions were located around the Great Lakes, Pacific Northwest, and Upper Midwest. Who's hoping Old Man Winter makes a comeback in December? ❄️ pic.twitter.com/HCpobbwYtB— NWS Weather Prediction Center (@NWSWPC) December 2, 2021
The National Weather Service reported high elevation snowfall lagging behind by 10 to 20 inches last month. This snowfall in the west is critical for filling the region’s largest natural “reservoir” — mountain snowpack.
Snowpack is the amount of water in the snow that rests on the ground, slowly building for the duration of the cold season. Once snowpack reaches its peak in the spring, it melts and recharges the soils, rivers and many reservoirs that provide water for millions of Americans.
The graph below shows the current snowpack accumulation for the Upper Green basin in western Wyoming compared to typical early season snowpack. By Nov. 1, current season snowpack (the black line) was tracking along with the median (green) line — then the tracks diverged.
Snowpack in the Upper Green basin commonly increases by 2 inches in November; this year, it increased by less than an inch. Basin snowpack is at a 1.5-inch deficit — at 56 percent of normal.
The Upper Green basin isn’t alone. Every basin in the west is below normal, ranging from as little as 2 percent of normal on the Lower Colorado in Arizona to 81 percent of normal for the Upper Columbia in Washington.
There’s still time
It’s a pretty bleak picture for the start of winter. The bad news is that early season snowpack is an important contribution to the peak snowpack. The good news is that 1) we’ve got a lot of time left, and 2) we can still make up these deficits.
Projection graphics produced by the USDA Natural Resources Conservation Service (NRCS) show current basin snowpack and projections of possible future accumulations to peak. These projections are based on the history of the SNOTEL stations in the basin.
For the Central Lahontan basin (Lake Tahoe and surrounding area), the most likely scenario (50th percentile line) is for below-normal peak snowpack. In other words, if the basin receives average snowpack for the rest of the cold season, peak snowpack would be about 80 percent of normal — hence why early snowpack is important for overall accumulation.
The 70th percentile shows a more aggressive scenario, where the basin gets an above-average snowpack for the rest of the season. Peak snowpack would then be near normal. This scenario is harder to achieve (about a 30 percent chance), but not out of the realm of possibility.
Most of the basins around the West show a similar story: average snowpack for the rest of the cold season would result in lower peak snowpack, but normal peak snowpack is still technically within reach.
One factor that can affect the region’s winter precipitation is the current La Niña, which is likely to continue through the winter and into the spring. While it’s not always a perfect relationship, we tend to see above-average snowfall in the northwest and below-average snowfall in the southwest during La Niña winters.
If this pans out, the Pacific Northwest and northern Rockies are more likely to get average peak snowpack, but the southern basins would more likely peak below average.
One other challenge to contend with is the temperature outlook. The Climate Prediction Center’s seasonal outlook calls for a greater chance of above-average temperatures for Utah, Colorado and to the south. Above-average temperatures for the lower elevation areas would increase the likelihood of melting, and could also result in earlier and lower peak snowpack. The Pacific Northwest is expected to see below-average temperatures.
With the La Niña and temperature forecasts, the odds are better for Washington, Oregon, Idaho and Montana to have a decent winter, even after a poor start. Northern California, the Great Basin, Wyoming, and the northern reaches of Utah and Colorado could also recover. The areas that are likely to be in the worst shape in the spring would be the central and southern mountains of Utah and Colorado and the rest of the Southwest.
It’s still early enough in the season for things to turn around, however, so let’s all hope for some holiday magic in the form of snowflakes!
Becky Bolinger is the assistant state climatologist for Colorado and a research scientist at Colorado State University.