Projected changes in cut-off lows and their implications for North American extreme precipitation events

Cut-off low (COL) pressure systems, synoptic-scale phenomena with substantial influence on regional weather patterns, raise critical concerns regarding their dynamics in a changing climate. However, uncertainties persist regarding future COL changes and their attributes. This study investigates future changes in COLs and their impacts in North America, using a multimodel ensemble of state-of-the-art climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), with spatial resolutions from 250 to 50 km. Employing a feature tracking algorithm to a common set of models, encompassing historical simulations (1980-2009) and future projections (2070-2099) under a high-level greenhouse gas emission scenario (SSP585), comprehensive insights emerge concerning projected COL changes, including frequency, intensity and precipitation patterns across North America's seasons. Our findings show a notable, consistent increase in summer COL track density over the northeast Pacific and western United States (US), contrasting with robust decreases in total COL numbers during winter and spring. Spring COLs are projected to shift equatorward, impacting western North America, the southern US, and the Gulf of Mexico. While climate models exhibit limited confidence in predicting COL intensities, projections indicate a robust increase in extreme summer and spring rainfall events in the future climate, particularly within models projecting a significant increase in COL frequency. The projected increase in summer COL activity and the associated extreme precipitation events draws attention to the importance of understanding COL-related precipitation dynamics for climate change adaptation strategies.

Keywords: Cut-off lows, CMIP6, multimodel ensemble, climate projections, extreme precipitation events, North America.