Snowpack

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Overview

Figure 1. Colorado River Basin modeled average April 1st snow-water equivalent (SWE; left) and modeled average annual runoff (right). Note that areas producing >1" of runoff closely coincide with those that have a consistent April 1st snowpack. Maps: Figure 2.3, State of the Science Report (Lukas and Payton 2020); data: Livneh et al. 2013

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 snow and occasionally deposit dust on the snowpack, and abnormally sunny and warm spells that drive sublimation in the winter and rapid snowmelt in the spring. The aggregate of these events and their complex interactions with the terrain and vegetation cause each year's snowpack to evolve in a unique way, while still following some general patterns in space and time.

Monitoring of the basin's snowpack has long relied on observations at hundreds of snow courses and automated SNOTEL stations. More recently, this backbone network of in-situ observations has been increasingly augmented by satellite and airborne remote sensing of the snowpack, citizen snow observations, and modeling that integrates varied snow observations with weather data to provide a finer-grained, spatially explicit picture of the snowpack.

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

Note: 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

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 snow products based on in-situ data

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.

Gridded snow products based on remotely-sensed data

ASO (Airborne Snow Observatories, Inc.) - Basin Map

ASO uses airborne lidar to measure snow depths across a basin on demand; these depth measurements are combined with snow-density modeling to estimate SWE with high accuracy at 50-m spatial resolution. Free registration required to view the data for all ASO-flown basins.

Other snowpack information

Colorado Dust-on-Snow (CODOS) reports

The CODOS program at the Center for Snow and Avalanche Studies (CSAS) tracks the deposition and emergence of dust layers in the snowpack, and snowpack temperature and other metrics, at 11 mountain pass locations throughout Colorado.


Additional resources

State of the Science Report

Chapter 2 of the State of the Science report, Section 2.5, provides an overview of the basin's snowmelt-dominated hydrology and key snowpack processes and patterns.

Chapter 5 of the State of the Science report, Section 5.1, describes the different methods for snowpack monitoring in much greater detail, along with links to several snow-monitoring tools.

Snowpack Monitoring in the Rocky Mountain West: A User Guide

This user guide expands on Section 5.1 of the State of the Science report with guidance on selecting appropriate snow-monitoring data and tools, and guidance on accessing and using the different online tools.