An Investigation of Mesoscale Precipitation Distribution Sensitivity to Cyclone Tracks in the Complex Terrain of California

Precipitation distribution in California varies widely. The complex terrain surrounding the Central Valley plays a significant role in precipitation distributions. In addition to large-scale forcing, the mesoscale precipitation distribution is dictated by the incoming storm system, atmospheric river, low-level and barrier jet, and orographic lifting and blocking. We hypothesize that the rainfall patterns over the California mountain ranges are influenced, not only by the large scale flow direction, as noted in previous research, but also by the track of approaching extra-tropical cyclones, as the orientation of the low-level flow varies. Therefore it is important to understand the dynamics of these storms, as they pertain to different tracks California coastal range and Sierra Nevada. Three track types, with the storm center and/or circulation coming in contact with the mountain complex are analyzed in this study; I) cyclones moving from southwest to northeast, II) cyclones moving from west to east, III) cyclones moving from northwest to southeast. The precipitation distributions associated with each track type are investigated by two methods; first with observed precipitation and North American Regional Reanalysis data, and second by model simulations with the Weather Forecasting and Research (WRF) Model Version 2.1.2. The role of orographic blocking of flow entering the Central Valley and how the blocked flow transports moisture to different locations is investigated, as it pertains to storms of the three track types. In addition, the WRF model allows for high resolution analysis of observed fine scale phenomenon, such as the barrier jet and local eddies, that otherwise are limited by the spatial resolution of observations. Localized areas of convergence appear throughout the Central Valley, and are hypothesized to be influenced, in part, by the circulation around the cyclone center. The understanding and classification of these mesoscale can assist in the forecasting and further research of mesoscale precipitation distributions in the region.