Low-elevation snow stacks up this season: Experts unsure why SNOTEL sites below 10,000 feet performing better than high-elevation sites — @AspenJournalism #snowpack (March 6, 2023)

This SNOTEL site at about 8,774 feet at the top of McClure Pass was measuring 154% of median snowpack on March 1, 2023. Lower elevation SNOTEL sites across the West Slope are showing a higher percentage of median snowpack than those at a higher elevation (above 10,000 feet). CREDIT: HEATHER SACKETT/ASPEN JOURNALISM

Click the link to read the article on the Aspen Journalism website (Heater Sackett):

Snowpack on the Western Slope is tracking above average for this time of year, which has some forecasters feeling optimistic about spring runoff. But there is also an interesting phenomenon that they don’t yet know what to make of.

The snow-water equivalent — a measure of how much water is contained in the snowpack — for the headwaters of the Colorado River stands at 116% of average. That number is measured by snow telemetry (SNOTEL) sites, which are remote sensing stations throughout the West’s mountainous watersheds that collect weather and snowpack data.

Most of the lower-elevation SNOTEL sites (10,000 feet and below) have a higher percentage of median snowpack than high-elevation sites (above 10,000 feet). For example, in the Colorado basin, low-elevation SNOTELs are at a combined 121% of average while high-elevation ones are at 112% of average.

This trend holds true across the Western Slope with the Gunnison, Southwest and Yampa/White/Green river basins at 155%, 152% and 142% of average, respectively, for low-elevation sites and 119%, 136% and 122% for high-elevation sites. In the Roaring Fork basin, snowpack is at 110% for the four high-elevation sites and 134% for the four low-elevation sites.

“I can pretty confidently say sites below 10,000 feet have that trend pretty clearly exhibited,” said Karl Wetlaufer, a hydrologist and assistant supervisor at the National Resources Conservation Service’s Colorado Snow Survey. “It’s certainly an interesting observation.”

Why this counterintuitive trend is occurring is unclear. This winter’s storm patterns may be favoring lower elevations. Or colder-than-average temperatures and overcast days in February may have allowed the snowpack at lower elevations to continue accumulating. The February temperatures for western Colorado were on average about 2 degrees below normal, according to the NRCS.

“We’ve been cloudier, colder, and that has probably helped prevent some melting at lower elevations that might typically take place,” said assistant state climatologist Becky Bolinger. “We will definitely want to look into why the lower elevations are performing so much better than the higher elevations.”

Snowpack above average

Snowpack overall on the Western Slope is above average, with some basins — the southwest, which includes the San Miguel, Dolores, Animas and San Juan rivers and the northwest, which includes the Yampa, White and Little Snake rivers — already surpassing the average seasonal peak. Snowpack typically peaks the first week or two in April.

What more snow at lower elevations means for the timing of this spring’s runoff is also unclear, but forecasters say runoff volume should be above average.

“Big picture, this year is looking very, very favorable for all of western Colorado, and it’s a really big turnaround from the last couple of years,” Wetlaufer said. “It’s kind of tough to parse out the impact of this lower-elevation snow being at a higher percent of median than higher-elevation snow, but, in a general sense, I would certainly say it’s quite encouraging for ample snowmelt runoff this season.”

This is partly because lower elevations encompass more surface area than higher ones; there is simply more land below 10,000 feet than above, and if it is covered in an above-average snowpack, that is a good thing for streams and soils.

“Having that lower-elevation snowpack is going to help keep soil-moisture levels high, which can help the efficiency of the higher-elevation snow when it does melt at a later date,” Wetlaufer said. “Substantial low-elevation snow is going to wet up the soil conditions and allow most of that snowmelt to actually transition to the stream channel.”

In recent dry years, thirsty soils have sucked up runoff before it made it to streams. For example, 2021 was historically bad, with an upper basin snowpack that peaked about 90% of average but translated to only 36% of average runoff into Lake Powell, according to the U.S. Bureau of Reclamation. It was the second-worst runoff on record after 2002.

Although water managers are feeling confident that this year will be better and give a boost to depleted reservoirs in Colorado, they caution that one good year is not enough to pull the entire system out of a crisis. Lake Powell, which is the storage bucket for the upper basin states of Colorado, Utah, New Mexico and Wyoming, is at about elevation 3,521 feet, or about 23% full, the lowest since filling.

“Is this going to solve the Lake Powell and Lake Mead crisis? Not even close,” Bolinger said. “But the forecasted inflows into Powell are above average right now. There’s a silver lining there.”

Aspen Journalism covers water and rivers in collaboration with The Aspen Times.

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