Atmospheric River impacts in British Columbia and the Pacific Northwest on 22-24 January 2015 during the CalWater 2015 field campaign

Abstract:

Over 30 dropsonde transects were performed across atmospheric rivers (ARs) over the eastern Pacific during CalWater 2015. An event in late January allowed first-of-its-kind coordinated dropsonde transects of an AR using the NOAA G-IV aircraft in tandem with the NOAA Ronald H. Brown (RHB), which observed the marine boundary layer during the passage of this major AR. Dropsonde data collected on 22 January 2015 sampled the early stages of the AR, when the AR began making landfall near Vancouver Island, British Columbia. At the same time the RHB collected precipitation and oceanic moisture flux measurements on the warm side of the AR. A second flight on 24 January 2015 sampled the later stages of the AR, again passing over the RHB stationed beneath the AR. During this later period, the AR axis of moisture shifted north-northeast and fanned out along the coast, affecting regions from Northern Washington to Southern Alaska. Multi-day landfalling AR conditions led to flooding in British Columbia and northern Washington. The influence of the coastal orography combined with the shift in AR orientation is examined to understand the orographic control of precipitation that triggered the flooding. In addition, cross section analysis of the AR using dropsonde and reanalysis data are used to better understand the synoptic influences, water vapor transport, and moisture evolution during the lifecycle of the AR. To gain greater insight into AR development and prolonged AR conditions that led to enhanced flooding, a comparison of aircraft and ship data from CalWater 2015 and NOAA Unique CrIS/ATMS Processing System (NUCAPS) retrievals (integrated water vapor, vertical temperature and moisture profiles, and an experimental ATMS-only rain rate product) will be compared for the 22-24 January period.