A stretched Polar Vortex and North American and Eastern Asian Cold-Air Events during January/February 2025

During mid-January through February 2025 the low-level stratospheric polar vortex (LSPV) at 100 mb extended from North America across the pole to east-central Asia, a stretched pattern, coinciding with a period of extended cold weather on both continents. The LSPV, and its associated tropospheric blocking projections, were a main organizing feature. Weather events were mostly contained in the tropospheric west-east wave guide. For the United States (US), cold conditions occurred in a corridor that includes Illinois, through Mississippi and Virginia. During the second half of January, a 500 mb ridge-trough was set up off the west coast of California, driving cold temperatures into the southeastern US, with record snow in New Orleans. During early February there were cold events in Korea and Eastern Asia; an intermediate timing between cold air outbreaks in the US. The end of February saw a second US cold air outbreak. Although the stretched LSPV at 100 mb had a one and a half month duration extending over the subarctic, mid-tropospheric weather events were of shorter duration in both the US and Eastern Asia. The troughing at 100 mb in the stretched LSPV pattern coincided with event-based barotropic atmospheric troughing response at lower levels. Tropospheric weather events can coexist with the LSPV and thus contribute to sub-seasonal forecasting.