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A Lagrangian approach is applied to explore the evaporative moisture sources within the boundary layer for 103 wintertime extreme precipitation events over South China during 1979China during -2013 Oceanic sources provided about 67.7% of the moisture for these extreme precipitation events, with terrestrial sources providing the remaining parts. The five most important moisture source regions were the South China Sea (30.

The formation mechanism for wintertime extreme precipitation events over the southeastern Tibetan Plateau (SETP) is explored. The crucial step in the development of these events was the emergence of a cyclonic anomaly above the Tibetan Plateau. Wave activity fluxes along a Rossby wave train embedded in the subtropical jet stream (i.e., the circumglobal teleconnection) played the dominant role in producing this cyclonic anomaly, supported by weaker wave activity fluxes along a second Rossby wave train originating over Scandinavia. The cyclonic anomaly then moved over the SETP, favored strong updrafts, large‐scale moisture convergence, and intense precipitation. Extreme precipitation was more likely to ensue when the arrival of the cyclonic anomaly was preceded by persistent warm anomalies over the SETP, which favored moisture accumulation there. Temperatures above the SETP dropped sharply around the onset of the extreme precipitation. A heat budget analysis indicates that adiabatic cooling associated with convective ascent along the downstream edge of the cyclone played a leading role in this temperature drop, while a cold air intrusion associated with an anticyclonic anomaly over western Siberia (one center of action along the second wave train) played a complementary role. An Eulerian moisture budget analysis shows that variations in precipitable water delayed the onset and enhanced the intensity of these events, with moisture for precipitation delivered to the SETP mainly through the western and southern boundaries. A companion Lagrangian moisture source analysis reveals that the land areas south of the Tibetan Plateau typically contributed 78.7% of the moisture supply for these events.

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This study examines the synoptic impacts of wintertime extratropical cyclones on northeastern China. The 181 analyzed cyclones mainly originate from eastern Mongolia and dissipate over the North Pacific Ocean. Precursor negative geopotential height anomalies for these cyclones emerge over continental areas near the Barents and Kara Seas. Baroclinic instability and midlatitude westerly winds are the dominant factors driving the development and movement of these cyclones from their precursor signals. Owing to the southeastward migration of the cyclones, temperature over northeastern China first increases and then decreases, resulting in a significant increase in the frequency of extreme weather. These cyclones contribute about 70.6% of the extreme precipitation days over northeastern China. Relative moisture contributions from the East China Sea, the Sea of Japan, and East Asia are all anomalously large during cyclones associated with extreme precipitation days, with moisture from these regions entering northeastern China mainly through its southern and western boundaries. Temperature variations over northeastern China play a critical role in the accumulation of moisture for extreme precipitation and the timing of that precipitation. Moisture transport initially contributes to an increase in precipitable water due to warm temperature anomalies. The added precipitable water is then released as extreme precipitation when the atmosphere over northeastern China starts to cool.