In October 2023, North and Northeast China experienced a record-breaking extreme high temperature event (EHTE), with monthly mean surface air temperature (SAT) 3℃ above normal, posing a grand threat to crop production and ecological environment. The primary driver of the EHTE was an anomalous large-scale barotropic high-pressure (anticyclone) centered over Lake Baikal. The lower to middle levels northerlies over the southeastern flank of the anomalous anticyclone suppressed air moisture and cloud cover over North and Northeast China, which increased downward shortwave radiation and consequently elevated SAT in the region.
A comparison of global circulation and sea surface temperature (SST) anomalies in October 2023 with historical anomalies associated with SAT over North and Northeast China during 1979–2022 suggests that abnormal North Atlantic tripole (NAT) SST anomalies and the Indo-Pacific zonal SST gradient (IPG) were potential origins of the record-breaking EHTE. Further observations and numerical simulations demonstrated both the NAT and IPG triggered downstream- and poleward-propagating Rossby wave trains. These wave trains contributed to the formation of the anomalous high-pressure over Lake Baikal, leading to reduced cloudiness and elevated SAT over North and Northeast China.
A physical-based prediction model, utilizing the precursors from the two oceanic origins, outperformed the two dynamical models with lead time from zero to three months. It successfully predicted the record-breaking EHTE in 2023, a feat that the dynamical models failed to achieve.

Record-breaking October high temperature, North Atlantic tripole SST, Indo-Pacific zonal SST gradient, Physical-based seasonal prediction