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 snowpack of the basin is effectively an enormous reservoir that fills and empties every year. This reservoir has average seasonal peak volume of 17–18 maf in the Upper Basin, equivalent to 70% of the capacity of Lake Powell.

As discussed in Climate patterns and variability, a disproportionate share of basin-wide precipitation occurs in the high-elevation headwaters, where it falls primarily as snow, and then tends to persist as snow until the spring, because of the cooler temperatures and lower evapotranspiration losses there. The area in which the seasonal snowpack consistently builds and melts comprises only about 10% of the Upper Basin, and less than 3% of the lower basin

Broad aspects of the spatial distribution and evolution of the snowpack are fairly consistent from one year to another, such as more snow with increasing elevation, and more snow on west-facing sides of mountain ranges. However, the details within these generalized patterns can vary greatly from year to year. Many individual weather events shape the snowpack: storm dynamics 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, give each snow season and basin snowpack a unique form over space and time.

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

Weather station data

MesoWest

This site created by the University of Utah provides map-based access to 1000s of observations from the NWS and FAA (ASOS/AWOS) automated networks, RAWS, SNOTEL, APRSWXNET/CWOP (citizen weather stations), and many other networks. Very useful for real-time monitoring of temperature, winds, humidity, and recent precipitation; users can also access historical observations.

ACIS Climate Maps (HPRCC)

These maps, generated from weather station observations from the NWS COOP network and updated daily, are very helpful for monitoring conditions from weekly to annual timescales. Note that the "shaded" maps are created using a very simple interpolation, unlike that used for gridded climate products.

Gridded climate products

NOAA NCEI Climate at a Glance

This versatile tool can be used to generate many types of charts, maps, and analyses from NOAA’s official nClimGrid gridded climate dataset, updated monthly.

Climate Toolbox

This toolset, developed by researchers at the U. of California-Merced and partners, generates many different types of charts and analyses from the gridMET gridded (4 km) climate dataset, updated daily.

WestWide Drought Tracker

These maps display the PRISM gridded climate product, updated monthly, for climate (temperature, precipitation) variables as well as drought indices (PDSI, SPI, SPEI). The "Percentile" maps show how unusual recent conditions are relative to the historical record.

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.