Projections of Future Large-Scale Meteorological Patterns, Temperature, and Precipitation over the Pacific Northwest

Abstract:

Future projections of large-scale circulation patterns over the Pacific Northwest of North America and their associated surface temperature and precipitation are assessed in the 6^th phase of the Coupled Model Intercomparison Project (CMIP6). The self-organizing map approach is applied to reanalysis data from the Modern-Era Retrospective Analysis for Research and Applications, version-2 (MERRA-2) to cluster 500 hPa geopotential height (Z500) into 12 representative nodes that span the range of historical circulation patterns. CMIP6 data for Z500 are mapped to each node by a least Euclidean distance algorithm for historical and end of century ssp-585 experiments, and the resulting differences in Z500 node patterns and their associated temperature and precipitation are analyzed. Overall, the general range of patterns is not projected to change appreciably, but a reduction in amplitude of Z500 anomalies is found across meteorological seasons. The largest temperature increases in DJF are found in patterns historically associated with anomalously cold weather, while the largest temperature increases in JJA are found in patterns historically associated with hot weather. Precipitation is found to generally increase across seasons, however in some cases dry patterns becoming wetter and historically wet patterns become drier. Furthermore, significant changes in pattern frequencies are found across seasons, with a decrease in frequency of highly amplified Z500 anomaly patterns compared with the historical climate.