Mesoscale Climate Surprises over the Pacific Northwest: Initial Results of a Large High-Resolution Regional Climate Ensemble for 1970-2100

A number of studies have shown that orographic effects, regional variations in land surface characteristics, mesoscale weather systems, among other smaller scale phenomena are critical in determining the implications of global warming at finer scales, and particularly over the western U.S.. For the western U.S., there is substantial research and experience that suggest that a minimum resolution of approximately 15-km grid spacing is required to provide realistic simulations of important orographic and land-surface related mesoscale processes. Global climate models run at grid spacings ranging from 100-250 km are inadequate to properly simulate the impacts of regional terrain, coastal configurations, and more. Of particular interest is whether high-resolution climate simulations might result in regional projections significant different from global models, and whether they might be “mesoscale surprises” as the region and planet warms.

This presentation will describe the initial results of a 12-member regional climate ensemble covering the Pacific Northwest using the Weather Research and Forecast (WRF) model run at 12-km grid spacing for the period 1970-2100. These runs were driven by 12 different CMIP simulations using the aggressive RCP 8.5 scenario. The result will describe the complexity of the regional climate response over the Pacific Northwest, including a range of mesoscale surprises including local declines in precipitation in the lee of barriers, increased cloudiness in spring, and reductions in offshore-directed flow.