LAS VEGAS (KLAS) — Denver’s first major snowstorm of the year brought nearly three times the average for all of November, dropping 20 inches by Saturday morning. Now, temperatures are already warming and melting what’s on the ground.
The Rocky Mountains west of Denver were on the edge of the storm’s crosshairs, and snowfall totals in the Upper Colorado River Basin are above average as winter approaches.
Snowpack — or snow water equivalent (SWE) — in the region that feeds the Colorado River is currently at 147% of normal for this time of year. The highest levels are in southern Colorado and northern New Mexico as of Nov. 11:
- Upper Green: 98%
- Lower Green: 115%
- White-Yampa: 101%
- Colorado Headwaters: 139%
- Gunnison: 190%
- Dirty Devil: 146%
- Lower San Juan: N/A
- Dolores: 279%
- Upper San Juan: 267%
(Totals as of Nov. 11 provided by the U.S. Bureau of Reclamation)
Snowpack measured in early November is no guarantee that weather patterns will continue to generate above-average numbers. The crucial measurements for communities downstream won’t come until early April at the end of the season. Last year, snowfall in January was preserved by cold temperatures in the Rockies, allowing the snowpack to build to 111% of normal by the first week of April.
The metro Denver area is east of the Continental Divide. Weather there is outside the basin that drains west and south as the Colorado River grows. Experts say the most critical areas to the river’s water supply are the Colorado Headwaters, which includes the western slope of Rocky Mountain National Park, and the Gunnison region in Central Colorado.
Stacking the numbers
While numbers from the southern regions of Delores and the Upper San Juan appear impressive, all the percentages are comparisons to 30-year average snowpack levels. As an example, the Dolores region usually averages 0.9 inches in early November, and 279% of that would be about 2.5 inches. The average in the Colorado Headwaters is usually 1.7 inches, and 139% of that would be 2.4 inches. The percentages mean much more in April, when the SWE averages for Delores are around 13-15 inches the Colorado Headwaters reaches 13-16 inches.
If those numbers seem small, it’s because the water content of snow isn’t the same as the number of inches that fall on the ground. According to the U.S. Department of Agriculture’s National Water and Climate Center, “The density of new snow ranges from about 5% when the air temperature is 14°F, to about 20% when the temperature is 32°F. After the snow falls its density increases due to gravitational settling, wind packing, melting and recrystallization.” There’s a big difference between “dry” snow you’ll sometimes hear called powder and “wet” snow that’s more common in late winter and early spring.
Just as last week’s storms in Denver showed, snowfall isn’t uniform. Some parts of the city were hit hard while others escaped. The SWE measurements maintained by the federal government for the Upper Colorado River Basin and other areas are collected by automated SNOTEL (snow telemetry) stations. There are about 900 of the sites in the western U.S.
The small amounts involved in the early season can cause wide fluctuations in the averages. Already this year, the SWE average has bounced around from 235% on Oct. 24 to 123% on Oct. 28 and back up to 168% on Friday, Nov. 8, before today’s 147% measurement.
In mid-October, a report from the National Oceanic and Atmospheric Administration (NOAA) pointed to a slowly-developing La Niña this year, which could bring drier-than average conditions for the Southwest.
Nevada, Arizona and California are grouped as Lower Colorado River Basin states. When a federal water shortage was first declared in August 2021, Lake Mead became a focal point as reduced water allocations went into place. The visible “bathtub ring” is a reminder of the ongoing megadrought that began in 2000.
The lake is currently at about 1,061 feet above sea level — about 168 feet below full pool. On July 27, 2022, Lake Mead hit its lowest point since the reservoir was filled — 1,041.71 feet.
LAKE MEAD:
Lakes Mead and Powell recovered to about a third full after very wet winter months in early 2023 characterized by a series of atmospheric rivers that fed moisture over the Rockies. Last year’s better-than-average totals helped sustain that recovery.
Today, Lake Mead is about 4 feet lower than it was a year ago, and 16 feet above its level in 2022.
The consecutive wet years opened a window for the government to put conservation programs into place and make needed repairs to aging infrastructure that was wasting water. A new plan to manage the Colorado River is in the works and must be in place when 2027 arrives.
