Projected changes to cold-season extratropical cyclones over northeastern North America in an ensemble of regional climate model simulations

Abstract. Extratropical cyclones (ETCs) are the main drivers of cold-season weather in northeastern North America (NENA), yet their response to climate change remains uncertain. Here, we assess cold-season (November–March) ETCs in a high-resolution (0.11°) regional climate model ensemble driven by four CMIP6 global climate models under multiple emissions scenarios, including five initial-condition members for one model–scenario combination. Historical simulations reproduce the main ERA5 track and genesis patterns, although they generally simulate more cyclones, lower minimum sea-level pressures, and stronger winds. With warming, cyclone track density decreases across much of North America, including over NENA, where cyclogenesis also tends to decline. The five-member subset exhibits substantial spread in projected track-density and cyclogenesis changes, highlighting the influence of internal variability on these regional patterns. Yet the total number of cyclones affecting NENA declines robustly across all driving models. Changes in cyclone characteristics are generally weak and driving-model dependent, although some statistically significant changes indicate stronger winds or slower-moving cyclones. Most apparent deepening in minimum sea-level pressure disappears when pressure is expressed as an anomaly from the local climatology, weakening the evidence for pressure-based intensification. Nevertheless, the number of cyclones falling below a fixed historical pressure-anomaly threshold remains broadly unchanged as total cyclone frequency declines, so the proportion classified as intense tends to increase. Despite fewer cyclones, total cold-season ETC-associated precipitation tends to increase over NENA land areas, including at every major city examined. These results point to fewer but wetter cold-season cyclones, with increasing ETC-associated precipitation despite limited dynamical intensification.