Projections of Large-Scale Atmospheric Circulation Patterns and Associated Temperature and Precipitation Over the Pacific Northwest Using CMIP6 Models

Projections of 500 hPa geopotential height (Z500) patterns over the Pacific Northwest of North America and their associated surface temperature, precipitation, and frequency of occurrence are assessed using models from the 6th phase of the Coupled Model Intercomparison Project (CMIP6). The self-organizing maps approach is applied to reanalysis data from the Modern-Era Retrospective Analysis for Research and Applications, version-2 (MERRA-2) to cluster daily Z500 anomalies into 12 representative patterns that span the range of historical circulation patterns. CMIP6 data for daily Z500 anomalies are mapped to each node for historical and end of century global warming experiments, and the resulting differences in Z500 anomaly patterns, their associated temperature and precipitation, and pattern frequency occurrence are analyzed. Models project a reduction in the amplitude of Z500 anomalies, with majority model agreement on significant reduction found in JJA and SON. The largest temperature increases in DJF are found for patterns historically associated with anomalously cold weather, while the largest temperature increases in JJA are found in patterns historically associated with anomalously warm weather. Precipitation is found to generally increase across all seasons and patterns, however some historically wet JJA patterns become significantly drier. Significant changes in pattern frequencies are found across seasons, with a general decrease in frequency of highly amplified Z500 anomaly patterns compared to the recent historical climate