Zoom Meeting ID: 92726597934
In regions of complex topography such as California’s Sierra Nevada, rapid and significant intrastorm changes in precipitation amount, type, and intensity can be beneficial, but can also contribute to flooding, ice, or snow events that impact hydrology and communities. The rain-snow transition elevation, or the elevation where snow melts into rain, is a key variable when studying mountain meteorology, hydrology, and storm impacts. Sudden, extreme vertical changes in rain-snow elevations, or atmospheric snow levels, can influence impacts, but have not been previously catalogued.

In this study, we design a detection algorithm for extreme snow level changes which are first defined as one-hour vertical changes of a magnitude equal to or greater than 400 meters. We consider snow levels obtained from ten vertically-pointing ground radars across California. The past six cool seasons are included. In addition to defining and detecting extreme changes in rain-snow level, extremes are described in terms of seasonality and variations by water year and radar. We also investigate relationships between extreme rain-snow elevation changes and atmospheric rivers - low-tropospheric corridors of enhanced moisture which form over near-tropical regions of the Pacific Ocean and can travel to reach land, contributing up to half of California’s annual water supply.