Sublimation of Snow (SOS) Project

In 2021, water users in the Colorado River Basin experienced an unexpected mismatch between winter snowpack and the resulting spring and summer runoff. Snowpack across the headwater basins reached around 80% of average, but snowmelt translated into Colorado River streamflows that were only 30% of average (not the expected 80%). Where did the water go? Understanding the dynamics of snow sublimation will be an important component in answering this complex question. Snow sublimation occurs when snowpack is lost to the atmosphere, turning directly into water vapor without melting first, bypassing the liquid water phase entirely. Snow sublimation may remove as little as 10% or as much as 90% of snowpack from the ground. However, much about the process is not well understood, and sublimation is one of the largest sources of uncertainty in hydrologic modeling. The Sublimation of Snow Project (SOS), supported by the National Science Foundation, will measure multiple processes related to sublimation. The project goal is to improve and communicate fundamental scientific understanding of when, where, and how much snow leaves the land surface to become water vapor.

The study aims to understand:

  1. What controls the mixing of air near the snow surface with air higher up in the atmosphere in cold and often windy mountain environments?
  2. How do these environmental conditions change the amount of snow that is lost directly to the atmosphere?  
  3. What is the best way to measure this? 

Using a suite of instruments, researchers can better understand how environmental conditions in the mountains contribute to snow lost to sublimation and recommend measurement and data analysis strategies for future sublimation studies.

A Unique Partnership of Scientists, Funders, and Acronyms

The East River Watershed, home to Colorado’s Rocky Mountain Biological Lab (RMBL,  pronounced “rumble”) was selected as the SOS project site as the area allows for partnership with other concurrent hydrologic studies, including the Surface Atmosphere Integrated Field Laboratory (SAIL), supported by the US Department of Energy, and the Study of Precipitation, the Lower Atmosphere and Surface for Hydrometeorology (SPLASH), supported by NOAA. The SOS project will deploy the Earth Observing Laboratory’s (EOL) Integrated Surface Flux System (ISFS) to measure near-ground atmospheric turbulence, energy exchanges, and snow mass.

The collection of field data and the concurrent discovery process will be documented throughout the SOS project and used to generate written materials, videos, and other outreach products to facilitate discussion with stakeholders, educate students in the sciences, and enrich cross-discipline dialogue. 

By collecting targeted measurements of blowing snow conditions, this project will also provide new insights into which processes are most important for understanding snow sublimation and help support research on hydrologic systems needed to model and prepare for future droughts.

Sublimation of Snow Project Team

Jessica Lundquist

University of Washington

Julie Vano

Aspen Global Change Institute (AGCI)
Research Director

Ethan Gutmann

National Center for Atmospheric Research (NCAR)

Daniel Hogan

University of Washington
Graduate Student

Eli Schwat

University of Washington
Graduate Student

Elise Osenga

Aspen Global Change Institute (AGCI)
Community Science Manager

Liz Carver

Aspen Global Change Institute (AGCI)
Communications Manager

Emilio Mateo

Aspen Global Change Institute (AGCI)
Climate Science Fellow


National Center for Atmospheric Research
Lawrence Berkeley National Laboratory, Department of Energy
Physical Sciences Laboratory, NOAA
WSL Institute for Snow and Avalanche Research SLF
Laboratory of Cryospheric Sciences, EPFL
National Center for Atmospheric Research
WSL Institute for Snow and Avalanche Research SLF
Rocky Mountain Biological Laboratory


This effort has been made possible through funding by the National Science Foundation (NSF).