The Documentation of Extreme Events: Two Case Studies in Utah, Water Year 2005

The Natural Resources Conservation Service (NRCS), formerly the Soil Conservation Service, has monitored mountain snowpack and precipitation in the Western United States since 1934. The automation of measurement sites began in the late 1970s and now over 700 SNOw TELemetry (SNOTEL) sites are installed, most reporting hourly. The established length of record and hourly records now make it possible to evaluate and document extreme hydrometeorlogical events. Two recent events in Utah brought attention to the current lack of protocol for documenting extreme events. During October 20 - 22, 2004 the twenty four hour precipitation intensities for six Utah sites exceeded the National Weather Service estimated 100-year average return interval, and eleven of seventy seven Utah sites with 15 years or longer record, measured the maximum twenty four hour precipitation intensity of record. A second event Jan 8th to 12th hit SW Utah with high intensity rains and snow leading to the flooding of the Santa Clara River and the destruction of over twenty homes.