Cause of the China Cold Outbreak Late DEC/early JAN 2020-21

Summary: The first month of meteorological summer produced a stratospheric warming event over Northeast Asia (Fig. 1). In response the weather atmosphere (i.e. troposphere) turned colder and an elongated polar vortex formed stretching from Mongolia to Northeast Asia (Fig. 2). Beneath the polar vortex very cold temperatures at ground level were generated taking on arctic intensity in Central Asia (Fig. 3). Inevitably this cold air source region ejected pulses of cold southeastward into the high population centers in China late in December. Accompanying the rapid temperature drop and coldest weather in over 10 years (including a 42-year record of -26C in Beijing) was a veil of snow cover. The snow cover has allowed the cold outbreak to last into early January across north and east portions of China (Fig. 4). The 15-day outlook indicates the cold air mass is in retreat as China turns warmer than normal (Fig. 5).

Fig. 1: Stratospheric warming occurs across Northeast Asia during December 2020.

Fig. 2: Beneath the warming stratosphere the weather atmosphere (i.e. troposphere) cools and contracts and a polar vortex is born.

Fig. 3: The polar vortex generates a huge cold air mass in December across Eurasia gradually gaining arctic intensity.

Fig. 4: During late December and early January the Central Eurasia cold air mass is ejected into China where historic snow and cold is generated.

Fig. 5: The latest 15-day forecast by ECM ENS indicates the recent chill in China retreats northward and China turns somewhat warmer.