Snowpack

Overview

In the Colorado River Basin, snow is a key component of the hydrologic cycle. Most of the basin’s annual streamflow—about 70%—originates as snowmelt. The basin's seasonal snowpack acts as an enormous reservoir that builds up and releases every winter and spring. This 'snow reservoir' is found almost entirely in the mountain ranges and high plateaus that cover only a small fraction of the total area of the basin.

The snowpack reservoir has average seasonal peak volume of about 18 million acre-feet in the Upper Basin, equivalent to 70% of the capacity of Lake Powell, but its size varies widely from year to year. Many individual weather events shape the snowpack: storms that build snow accumulations, wind events that redistribute and help sublimate snow, and heat waves that drive rapid snowmelt. The aggregate of these events, and their complex interactions with the terrain and vegetation, means that each year's snowpack evolves in a unique way over time and across the basin, while still following some general patterns.

Relevance

Variation in snowfall and the resulting size of the snowpack from year to year is the primary influence on the magnitude of seasonal (spring-summer), annual, and peak streamflows. Accordingly, monitoring the evolution of the basin's snowpack over the course of the winter and spring is critical to forecasting streamflow and managing water supply. Snow monitoring is also vital to other river-based interests, such as fisheries management and guided rafting.

Data and tools

Snowpack Monitoring in the Rocky Mountain West: A User Guide provides more detailed descriptions of the datasets and tools listed below, and guidance on using them.

SNOTEL and other in-situ snow data

NRCS Interactive Map

This very versatile tool provides a clear spatial overview of snowpack (SNOTEL) and other hydroclimate conditions across the western U.S., while allowing users to easily drill down into site-level data. Displays both near-real-time data (previous day) and historical data.

NRCS State Snow Survey Snow Products

• Colorado
• Utah
• Wyoming
• Arizona
• New Mexico

The NRCS state snow survey sites provide many additional options--varying by state-- for viewing current and historical SNOTEL and snow course data, including monthly summary reports (Basin Outlook Reports).

CBRFC Snow Groups

Provides current year's time-series plots of SNOTEL SWE averaged across multiple SNOTEL sites (“snow groups”) selected to represent a particular catchment or area; ~300 options for catchments within the Colorado River Basin and eastern Great Basin.

CoCoRaHS Interactive Map

Provides daily new snow depth and SWE, and snow depth and SWE on the ground, from the hundreds of volunteer CoCoRaHS observers in the basin. Select Map Options > What to map these snow variables.

Gridded and modeled snow products

NOAA NOHRSC - SNODAS Interactive Map

Provides access to SNODAS daily gridded SWE and other snow variables; the SNODAS model builds and maintains a snowpack based on weather data and also assimilates SNOTEL data.

SnowView – Snow-Water Artificial Neural Network modeling system (SWANN)

This tool, developed at the U. of Arizona, shows a daily gridded snow dataset (SWANN) that uses snow models, assimilated SNOTEL data, and machine-learning methods. Users can compare SWANN with SNODAS for a catchment of interest.

CBRFC Modeled Snowpack – Interactive Conditions Map

Interactive map that provides daily-updated modeled SWE for ~500 catchment-elevation zones in the Colorado River Basin and eastern Great Basin. These modeled SWE data are used as key inputs for CBRFC's seasonal streamflow forecasts.

Additional resources

State of the Science Report

Chapter 4 of the State of the Science report describes weather station data and networks, and gridded climate products, in much greater detail.