Changes in Extratropical Cyclone Precipitation and Associated Processes during the Twenty-First Century over Eastern North America and the Western Atlantic Using a Cyclone-Relative Approach

This study investigates the future change in precipitation associated with extratropical cyclones over eastern North America and the western Atlantic during the cool season (November-March) through the twenty-first century. A cyclone-relative approach is applied to 10 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) in order to isolate precipitation changes for different cyclone intensities and storm life cycle, as well as determine the relevant physical processes associated with these changes. The historical analysis suggests that models with better performance in predicting extratropical cyclones tend to have smaller precipitation errors, and the ensemble mean has a smaller mean absolute error than the individual models. By the late-twenty-first century, the precipitation amount associated with cyclones increases by 5%-25% over the U.S. East Coast, with about 90% of the increase from the relatively strong (<990 hPa) and moderate (990-1005 hPa) cyclones. Meanwhile, the precipitation rate increases by 15%-25% over the U. S. East Coast for the strong cyclone centers, which is larger than the moderate and weak cyclones. The relatively strong cyclones just inland of the U.S. East Coast have the largest increase (-30%) in precipitation rate, since these centers over land have the largest increase in low-level temperature (and moisture), a decrease (5%13%) in the static stability, and an increase (-5%) in upward motion during the late-twenty-first century. This east coast region also has an increase in cyclone intensity in the future even though there is a decrease in lowlevel baroclinicity, which suggests that the latent heat release from heavier precipitation contributes to this storm deepening.