Characteristics, trend, and precursors of extreme cold events in northwestern North America

The cold extremes along with record snowfalls in North America (NA) have attracted great concern for decades. In this study, we select 23 wintertime northwestern NA (NWNA) from 1981 to 2018 and find a significant weakening trend of their integrated yearly intensities. Strong northerlies advections over NWNA associated the events are driven by intensified southward Beaufort anticyclone at lower troposphere enhanced blocking high higher levels. A strong low-pressure anomaly extends stratosphere centered around 250–300hPa, where jet stream becomes stronger moves northwestwards. Meanwhile, under low system is deep more prominent surface NWNA. There meridional dipole structure height temperature mid-high latitudes, indicative negative phase Arctic Oscillation. Results further suggest that La Niña-like sea anomalies may serve as precursor NWNA, triggering Pacific America-like wave train including an active center which linked extending downward surface. However, ice concentration region snow cover continent during early autumn likely exert minimal influence on