Recently, an unusual scene of snow falling on fully bloomed cherry blossoms unfolded in Seoul and the eastern metropolitan area. In Seoul, the latest snow observed since records began in 1907 was noted, with 3 to 8 cm of snow accumulated in the mountainous regions of Gangwon.
According to the Korea Meteorological Administration and the scientific community on the 15th, the cause of this snowfall is a cut-off low-pressure system. A cut-off low-pressure system occurs when part of the meandering upper-level jet stream is severed, causing the low pressure to descend and become isolated. This phenomenon maximizes the temperature difference between the surface and the upper levels, making the atmosphere extremely unstable. As a result, various weather phenomena such as rain, snow, gusts, and hail occur simultaneously.
A cut-off low-pressure system is a natural atmospheric phenomenon that is not directly related to global warming. However, recent research indicates that climate change due to warming affects the timing and location of cut-off low-pressure systems.
Researchers from the Wegener Center at Graz University in Austria released findings in February analyzing how climate change impacts the seasonality and geographical distribution of cut-off low-pressure systems. The researchers analyzed weather data generated every six hours from 18 climate models across several regions, including Europe, Asia, and North America, to track the paths and intensity of cut-off low-pressure systems. As a result, they forecast that cut-off low-pressure systems may occur more frequently and with greater intensity due to climate change.
Douglas Maroun, a researcher at the Wegener Center, noted, "Cut-off low-pressure systems are expected to occur earlier and more frequently in regions north of 40 degrees latitude and East Asia," adding, "In particular, Canada, Northern Europe, Siberia, and China should prepare for heavy spring rains and prolonged precipitation."
In fact, examining the extreme weather events from last year reveals that the influence of cut-off low-pressure systems is becoming increasingly prominent. During the summer monsoon period last year, heavy rainfall exceeding 100 mm per hour was recorded at nine locations due to the impact of cut-off low-pressure systems and the North Pacific high-pressure system.
At the end of November last year, the highest amount of snow recorded in November was observed in Seoul, Incheon, and Suwon. In Seoul, 28.6 cm of snow accumulated in one day, breaking the record for the deepest snow observed in November since weather records began. This was also a result of the cut-off low-pressure system holding cold air and interacting with the higher sea surface temperatures in the West Sea, leading to explosive development of snow clouds.
The average sea surface temperature around the Korean Peninsula last year was 18.6 degrees, 1.3 degrees higher than the average of the past decade. Particularly, the sea surface temperature in September was 3.2 degrees higher than normal, reflecting extreme high-temperature phenomena in the ocean as well. Consequently, the moisture vapor evaporated from the surface of the sea supplied to the atmosphere acted as a factor enhancing precipitation and heavy snowfall.
Maroun stated, "Whether extreme weather phenomena escalate into disasters depends on flood defense infrastructure and early warning systems," adding, "Urgent structural responses, such as ecological restoration, as well as climate change-based policy design are necessary."
References
Communications Earth & Environment(2025), DOI: https://doi.org/10.1038/s43247-025-02078-7