Figure 1. The new snow-level radar at Pine Flat Dam
Figure 2. Example real-time image from the snow level radar
Figure 3. Current and planned deployments of snow-level radars at major watersheds across the State of California
February 18, 2011
New Network of Snow-level Radars Deployed in California
Researchers from the Cooperative Institute for
Research in Environmental Sciences (CIRES) teamed with engineers from
NOAA's Earth System Research Laboratory (ESRL)
to design, build, and deploy a new network of snow-level radars in California. Snow
level, the altitude in the atmosphere where snow changes into rain, is a
critical parameter influencing runoff in mountainous watersheds because it
determines the surface area of the watershed that will be exposed to rain
versus snow. When the snow level is above most or all of the terrain in a
watershed, a storm is more likely to produce enough rapid runoff to cause
flooding. If the snow level is low in a watershed, then
a storm increases the snowpack, providing valuable storage of water for
potential later use. The snow-level radar (Fig. 1) was
designed specifically as part of a project with the California Department
of Water Resources (CA-DWR) to provide a 21st century observing systems
to help address water resource and flood control issues. This project will
apply lessons learned from more than a decade of research on West
Coast winter storms conducted by ESRL and partners under HMT, including the
first-ever evaluations of operational snow-level forecasts that used an
earlier generation of radar technology.
The snow-level radar utilizes modernized frequency-modulated, continuous wave (FM-CW)
technology, which only uses less than a watt of transmitted power. This dramatically
reduces the price of the radar components. The snow-level radar can be built for
approximately 1/10th of the price of one of the current state-of-the-art
pulsed radars used for the same purpose. The radar operates at 2.835 GHz,
which is ideal for measuring the properties of precipitation because at
this frequency there is very little weakening of the radar signals by
precipitation. Snow-level detection (Fig. 2) is based on an automated
algorithm1 developed by CIRES and ESRL scientists.
A five-year agreement with CA-DWR calls for ten snow-level radars to be
deployed in key watersheds across the state. Four of these
radars have already been deployed at or near major California reservoir dams: Shasta
Dam, Colfax (above Folsom Dam), New Exchequer Dam, and Pine Flat Dam. Figure 3 shows where these radars are located along with the deployment
plan for the six remaining radars. The radars are part of an unprecedented
observing network that will provide critical information on the forcings of
extreme precipitation and flooding, as well as long-term climate
observations to help decision makers adapt to a changing climate.
White, Allen B., Daniel J. Gottas, Eric T. Strem, F. Martin Ralph, Paul J. Neiman, 2002: An automated brightband height detection algorithm for use with Doppler radar spectral moments. J. Atmos. Oceanic Technol., 19, 687-697.
White, A., B., D. J. Gottas, A. F. Henkel, P. J. Neiman, F. M. Ralph, S. I. Gutman, 2010: Developing a performance measure for snow-level forecasts. J. Hydrometeor., 11, 739-753.
1 U.S Patent #6,614,140, "Operational Bright-band Snow Level Detection Using Doppler Radar"