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Combined Role of Low- and Mid-level Jets and Atmospheric Rivers on Winter Precipitation in the Eastern Sierra Nevada
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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.