TY - Generic T1 - Effect of Snowpack Changes in the Central Sierra Nevada on Water Supply Forecasts in the Truckee River Basin T2 - 76th Annual Western Snow Conference Y1 - 2008 A1 - Lea, J. KW - Runoff forecasting, snow accumulation timing, Donner Summit, declining snowpack, water supply AB - Water supply forecasts rely on a historic record of precipitation, snow and streamflow. The snowpack in the central Sierra Nevada has been measured each year since the early 1900s. Currently the USDA Natural Resources Conservation Service and the California State Cooperative Snow Survey program measure snow in the Sierra Nevada and keep long term records of the snowpack. These long-term records are a good indicator of seasonal precipitation in the building of the snowpack in the region. A statistical analysis of the snowpack record at Donner Summit compared to Tahoe City precipitation reveals a shift in the relation that occurred in the late 1970s. This change in the relation of the April 1 snow and cumulative seasonal precipitation in the area is statistically significant at the 99.9% level. Since the late 1970s, there no trend has been observed in annual precipitation amounts and annual streamflow volume on the Truckee River. However a decrease in the amount of cumulative snowpack on April 1 in comparison to the seasonal precipitation of October through March between these two sites has been observed. This indicates that from 1980 to 2007 there has been more rain than snow compared to the previous 43 years. JF - 76th Annual Western Snow Conference T3 - Proceedings of the 76th Annual Western Snow Conference PB - Western Snow Conference CY - Hood River, OR UR - sites/westernsnowconference.org/PDFs/2008Lea.pdf ER - TY - Generic T1 - An Evaluation of SNODAS for Determining Snow Water Equivalent on Mount St. Helens T2 - 74th Annual Western Snow Conference Y1 - 2006 A1 - Lea, J. A1 - Reid, I. KW - Mt. St. Helens, floods, eruption, Toutle River, SNODAS, SNOTEL AB -

When Mount St. Helens erupted on May 18, 1980 melting snow and ice on the mountain enhanced a large debris flood wave from all sides of the mountain, creating exceptional flooding along the Toutle River in southwest Washington. Mount St. Helens became active again in September 2004. During both of these episodes there was considerable concern that another eruption would entrain the existing snowpack resulting in a devastating flood. The US Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS), National Water and Climate Center (NWCC) was requested to provide weekly snow water equivalent (SWE) on Mount St. Helens to the National Weather Service Northwest River Forecast Center (NWRFC) and North Pacific Division of the US Army Corps of Engineers for determining potential flood magnitude in the event of an eruption. In the 1980s the snowpack was determined from the NRCS SNOTEL station network located around the mountain. SNODAS uses a physically based, spatially-distributed energy and mass-balance snow model in conjunction with assimilated satellite, airborne and ground-based observations of snow covered area and SWE to determine several snowpack parameters and modeled SWE at a 1 km grid scale national coverage. The SNODAS system is compared to the traditional SNOTEL method of determining the snowpack at three elevation bands and four quadrants on Mount St. Helens. SNODAS provides an improved model of the snowpack SWE around Mount St. Helens.

JF - 74th Annual Western Snow Conference T3 - Proceedings of the 74th Annual Western Snow Conference PB - Western Snow Conference CY - Las Cruces, NM UR - sites/westernsnowconference.org/PDFs/2006LeaA.pdf ER -