LAS VEGAS (KLAS) — Snowpack levels have increased over the past week, building a deeper water supply for the Southwest U.S. in a welcome change from two decades of drought.

The Rocky Mountains are getting the leftovers of storms that continue to punish California. While much of the moisture is wrung out of the clouds by the time they reach the Rockies, it’s still building snowpack levels that were already about a third above normal.

The Snow Water Equivalent (SWE) stored in the Upper Colorado Basin is now at 142% of normal, according to data provided by the U.S. Bureau of Reclamation. Just a week ago, it was at 134%. The increases have been heaviest in the mountains in southwest Colorado and southeast Utah, but even the Colorado Headwaters region has increased to 127% of normal levels.

More than 40 million people rely on the Colorado River for water. As snow melts and flows downstream through Colorado, Utah and Arizona, it eventually reaches Lake Mead to supply 90% of Southern Nevada’s water.

Weather through this week could bring warmer temperatures to the central Rockies, and more snow isn’t a big part of the forecast until the last week in March.

Measurements taken around April 1 are usually regarded as the “peak” snowpack of the year, but this has been an unusual year all around.

The Snow Today website notes snow cover in the Western U.S. — the amount of land covered in snow — likely reached its peak on Feb. 1, which is five days earlier than usual. Looking at satellite measurements since 2001, “This February had nearly three times the area of snow cover of 2015, the lowest year on record and 6.1 percent less snow cover than 2008, the highest year,” according to Karl Rittger of the Institute of Arctic and Alpine Research and Mark Raleigh of Oregon State University.

The shoreline changes as water recedes at Lake Mead in this photo from early February, 2023. (Duncan Phenix / 8NewsNow)

That would make this the fifth-highest snow cover since 2001. That factors into SWE levels and also how long the mountain snowpack lasts. Land covered by snow produces less blowing dust — an important factor in the “brightness” of snow. Less dust means the snow reflects sunlight better, helping it last longer. Industrial soot and smoke from fires also make snow melt faster.

Scientists measure these factors as “snow radiative force” — and it’s the lowest it’s been in the 23 years since record-keeping began.

Do these measurements really matter? The Bureau of Reclamation thinks so, announcing today that they are opening applications for $11.75 million in “emerging snow monitoring technologies.”

The Snow Today website also looks at what really happened with La Niña, a weather pattern that typically brings drier conditions to the Upper Colorado River Basin.

“The 2023 La Niña winter has thus far produced snow patterns that are more characteristic of El Niño conditions, just without widespread SWE deficits in the north,” Snow Today reports.

“The pattern in the current snow cover and SWE maps seems to be reversed and more characteristic of an El Niño pattern,” the website reports.

A climate blog from the National Oceanic and Atmospheric Administration (NOAA) also notes how “atmospheric river” storms turned conventional wisdom on its head.

“This atmospheric river onslaught surprised many who were expecting a dry season, especially in the Southwest, not only because of the prolonged drought but also because La Niña tends to bring drier-than-average winter conditions to the region,” according to NOAA’s Nat Johnson.

The blog analyzes patterns and concludes that this year was just an exception — not a fundamental change in known La Niña patterns.