The Sierra Barrier Jet and Distribution of Precipitation in Northern California

Abstract This study uses wind profiler data to examine the characteristics of the Sierra Barrier Jet (SBJ) over 23 cool seasons (October 2000–March 2023) and its influence on precipitation in Northern California. The analysis identifies 439 SBJ events, with a mean maximum wind speed of 25.6 parallel to the Sierra, an average duration of 14.2 hr, and a typical altitude of maximum wind near 1.05 km. Previous studies show that many extreme cool‐season precipitation events occur when landfalling atmospheric rivers (ARs) and SBJs coincide. During the study period, 220 ARs made landfall at San Francisco with 65% of them containing an SBJ. Alternatively, only 43% of SBJs occurred during a landfalling AR at San Francisco. Stronger SBJs also tended to coincide with higher IVT and stronger ARs, while weaker SBJs aligned with weaker ARs. ARs with higher IVT values also more frequently contained an SBJ. A precipitation analysis revealed that SBJ events accounted for up to 40% of the cool‐season precipitation, with maxima from the coast north of San Francisco through the Central Valley and into the Mt. Shasta–Trinity Alps region. AR events similarly contributed up to 50%, with a similar spatial pattern. When SBJs and ARs occurred together, they produced more than 30% of the seasonal precipitation, with maxima across the coastal ranges and into the northern Central Valley. Zonal and meridional precipitation transects across Oroville (39.5°N, 121.6°W) further illustrates how SBJs and ARs enhanced precipitation over the northern Central Valley, the Sierra, and the Mt. Shasta–Trinity Alps region.