| Deep, narrow corridors of concentrated water vapor transport referred to as "atmospheric rivers" (ARs) are an important contributor to extreme precipitation in the western United States. This study takes a closer look at the climatology of AR events that generate precipitation on the eastern slopes of the Sierra Nevada, with a particular focus on the Tahoe region. Daily measurements of winter precipitation recorded at 7 cooperative weather stations in and around the Tahoe basin are examined for the period from WY1974--2012 and the Climate Prediction Center/National Centers for Environmental Prediction gridded daily precipitation analysis is used to extend these results along the length of the Sierra crest from WY1949--2012. An inventory of AR landfall dates is generated using the National Centers for Environmental Prediction-National Center for Atmospheric Research model reanalysis and rawinsonde data from Oakland (OAK) are used to look at upper atmospheric conditions, including the presence of vapor transport by low- and mid-level jets on storm days. Strong mid-level vapor transport needs to occur in tandem with low-level transport in order to achieve the most extreme two-day precipitation in the Tahoe basin. Furthermore, when low- to mid-level vapor transport was present on AR days, the magnification of two-day precipitation intensity decreased with distance from the Sierra Crest; on non-AR days the relative increase in two-day precipitation intensity due to low- and mid-level vapor transport did not vary based on distance from the Sierra Crest. |
