The Nature and Predictability of the East Asian Extreme Cold Events of 2020/21

Three extreme cold events invaded China during the early winter period between December 2020 to mid-January 2021 and caused drastic temperature drops, setting new low-temperature records at many stations during 6-8 January 2021. These cold events occurred under background conditions of low Arctic sea ice extent and a La Nina event. This is somewhat expected since the coupled effect of large Arctic sea ice loss in autumn and sea surface temperature cooling in the tropical Pacific usually favors cold event occurrences in Eurasia. Further diagnosis reveals that the first cold event is related to the southward movement of the polar vortex and the second one is related to a continent-wide ridge, while both the southward polar vortex and the Asian blocking are crucial for the third event. Here, we evaluate the forecast skill for these three events utilizing the operational forecasts from the ECMWF model. We find that the third event had the highest predictability since it achieves the best skill in forecasting the East Asian cooling among the three events. Therefore, the predictability of these cold events, as well as their relationships with the atmospheric initial conditions, Arctic sea ice, and La Nina deserve further investigation.

Automated summary

Three extreme cold events occurred in China between December 2020 and mid-January 2021, leading to drastic temperature drops and setting new low-temperature records. These events were associated with low Arctic sea ice extent and a La Nina event, with the third event showing the highest predictability in forecasting East Asian cooling. Further research on the predictability of these cold events and their relationships with atmospheric initial conditions, Arctic sea ice, and La Nina is warranted.