14 Feb 2011 am

1. Second Precipitation Episode: 14 UTC 15 Feb to 18 UTC 16 Feb Motivation and Case Overview First Precipitation Episode: 04 UTC 14 Feb to 08 UTC 15 Feb U40° = Horizontal airflow toward 40° U340° = Horizontal airflow toward 340° U70° = Horizontal airflow toward 70° U40° = Horizontal airflow toward 40° U340° = Horizontal airflow toward 340° U70° = Horizontal airflow toward 70° • The modification and redistribution of precipitation in Atmospheric Rivers (ARs) by low-level barrier airflows associated with California’s coastal mountains and Sierra Nevada is not well understood. • The most important of these barrier airflows is likely the Sierra Barrier Jet (SBJ), which is a dominant feature in Sierra Nevada storms during the cool season. • Winds reaching the mountain range often are partially stalled and, in part, diverted along the range rather than directed up and over. Knowledge of the impact of the resulting terrain-parallel barrier jets on storm structure and precipitation distribution remains elusive. • This presentation provides an overview of the three-dimensional structure and evolution of a pair of SBJs and ARs observed during 14-16 February 2011 as part of the third Intensive Operating Period of CalWater 2011 Atmospheric River Atmospheric River Wind Profiler Analysis Wind Profiler Analysis Sierra Barrier Jet Sierra Barrier Jet A11A-0043Three-dimensional structure and evolution of the Sierra Barrier Jet: A CalWater case study from 14-16 February 2011*David Kingsmill1,2; Paul J. Neiman2; Sandra E. Yuter3; Mimi R. Hughes1,2; Benjamin Moore1,2* David.Kingsmill@colorado.edu1University of Colorado, CIRES 2 NOAA/ESRL Physical Sciences Division 3 North Carolina State University Cross-Sierra cross section Cross-Sierra cross section Waves behind front? 1200 UTC 14 February 2011 (Period 1) 0000 UTC 16 February 2011 (Period 2) Two different periods of large-scale AR conditions resulted in two different episodes of precipitation: 500 mb Height, Abs. Vort. & Winds 925 mb Height & Geostrophic Winds 500 mb Height, Abs. Vort. & Winds 925 mb Height & Geostrophic Winds Atmospheric River Atmospheric River Sierra Barrier Jet Sierra Barrier Jet Waves behind front? Vertically Integrated Water Vapor Flux Magnitude and Direction Vertically Integrated Water Vapor Flux Magnitude and Direction SSM/I Composite: 15 Feb 2011 PM Overpasses SSM/I Composite: 14 Feb 2011 AM Overpasses 15 Feb 2011 pm 14 Feb 2011 am Study Area Study Area Atmospheric River Atmospheric River Scattered Precipitation Echoes Widespread Precipitation Echoes Relatively weak large-scale dynamics Relatively strong large-scale dynamics Cold Front Sierra Barrier Jet Sierra Barrier Jet Atmospheric River Period 2 Period 1 Two distinct peaks in upslope wind speed, integrated water vapor and water vapor flux along the coast at BBY. Both peaks exceed thresholds for AR conditions Shallow, convective echoes Distinct brightband lowers on approach to terrain Brightband is not evident Period 2 Period 2 Period 1 Period 1 Tropopause Lowering • Water Vapor Flux • at LHM: • Higher-valued during Period 1 • Deeper during Period 2 • Weak large-scale dynamics, no apparent cold-frontal passage. • Scattered precipitation, 30-40 dBZ maximum echo, 2-4 km maximum echo top. • SBJ winds of 20-24 m/s (U340°) that are terrain-following. • AR winds greater than 24 m/s (U40°,U70°) that ride up and over SBJ. • SBJ extends about 90 km southwest of LHM, which is still slightly northeast of CCR. • Strong large-scale dynamics, distinct cold-frontal passage. • Widespread precipitation, 40-50 dBZ maximum echo, 3-7 km maximum echo top. • SBJ winds of 20-24 m/s (U340°) that are terrain-following. • AR winds greater than 32 m/s (U40°,U70°) that ride up and over SBJ. • SBJ extends about 70 km southwest of LHM, which is still northeast of CCR. Cold Frontal Passage