The season’s latest snowpack numbers in the Western United States are a big improvement from where they were in early December. But there’s a lot of winter left, and long-term drought remains an ever-present hurdle. So where are we, and what’s to come?
Let’s start with the good news. Since early December, weather patterns have boosted snowpack across the West to above-normal levels for this time of the year.
On Dec. 1, snowpack across most of the basins in the West was less than 75 percent of historical norms; many were below 25 percent. Starting Dec. 10, a series of atmospheric rivers and snow events erased those deficits. By January, basin totals in California had increased to about 200 percent of normal. California ended the month much wetter than average, which was much needed, since seven of its last 10 winters have been drier than average.
In Colorado, all Snow Telemetry (SNOTEL) stations showed that snowpack was below the 50th percentile in early December. In early January, nearly half of the stations reported in the 75th percentile. Wolf Creek Summit, one of Colorado’s highest-elevation observation sites, reported an impressive 18-inch increase in snowpack.
Current snow cover is holding steady across the mountain areas, with the highest elevations at around 50 inches or more of snow depth, and mid-elevations between 20 and 50 inches. In Mount Rainier National Park in Washington, the Paradise Ranger Station is reporting snow depth of 110 inches (after reporting 100 inches of snowfall over one month).
The shift from dry conditions to a wet pattern has been evident in the U.S. Drought Monitor. Most high-elevation areas have seen a one-category improvement in drought from Dec. 14 to Jan. 11. Isolated areas in California, western Nevada, northern Idaho, western Montana and northern Colorado have seen two-category improvements.
In Utah, “extreme” to “exceptional” drought conditions covered more than half the state from September 2020 until Dec. 28, 2021. As of Jan. 18, only 30 percent of the state was in extreme drought, with no areas under exceptional drought. Since early December, severe to exceptional drought conditions also eased in Idaho, decreasing by nearly half.
While there’s a lot of good news to go around, how much impact this short-term recovery will have in the long term remains to be seen. A couple of key points to keep in mind are 1) soil moisture deficits still exist, and 2) there’s a lot more snow season to go.
Soil moisture deficit is the first to get filled when the snowpack starts to melt in the spring. Across the West, soil moisture in the fall, just before the ground froze, ranked in the driest percentiles for much of the region, except in portions of Washington.
The Colorado Basin River Forecast Center accounts for those soil moisture deficits when estimating inflows into Lake Powell for seasonal water supply forecasts. Inflows into the reservoir are at 95 percent of average. While near average isn’t so bad (and much better than last spring, which was near record low), it isn’t quite enough to help erase the long-term drought situation that’s been plaguing the major reservoirs since the early 2000s.
We also need to keep an eye on the rest of the cold season. Being in a good position on Jan. 15 is good. For meaningful recovery, though, we need to be in that good position on March 15, April 15 and into May.
Ideally, the Lower Sacramento Basin in California would continue accumulating about 16 inches of snowpack from now until mid-March to keep up with historical norms. The Clearwater Basin in Idaho needs an additional 11 inches, and the Weber Basin in Utah needs another 10. Above-average snowpack now can quickly switch to below average with a few missed storms or a stubborn ridge of high pressure.
La Niña is expected to continue into the spring. For the Northwest, the wet pattern is likely to continue, which means snowpack will probably remain in good condition.
For the Southwest, it’s going to be tough. Precipitation is likely to be less than average for Arizona, New Mexico, and the southern portions of California, Nevada, Utah and Colorado. If the outlook pans out, expect to see those spring water supply forecasts decrease and for drought to persist through the summer months.