Intra-storm Variability in Sierra Nevada Spillover Precipitation

The extent of precipitation spillover into the lee of the Sierra Nevada significantly affects the region’s hydrology. For example, during the winter (Oct.-Apr.) of 2016-2017 many areas in western Nevada, including Reno, set new records for seasonal precipitation due to high occurrence of spillover events. While some of the factors impacting variations in lee side precipitation are well known, e.g., the number of intense atmospheric rivers, the mesoscale factors affecting intra-storm variability in spillover are less studied and remain poorly understood.

To address this knowledge gap, we use NEXRAD radar from KRGX near Reno, NV to document variations in lee side precipitation throughout the 2016-2017 cool season. The radar data are used to produce Hovmöller diagrams that reveal preferential cutoff locations for precipitation and episodic periods of enhanced spillover. The NEXRAD data are also used to produce along wind cross sections that demonstrate links between the structure of the mountain wave over the Sierra crest and the extent of spill over precipitation. These observations are further contextualized with radiosonde and model analyses in order to examine the impact of lee side stratification and upstream Froude number on spillover extent.