Winter westerly disturbances (WWD) are the primary climatic influence within High Mountain Asia during the boreal winter. Here we investigate variations and changes in WWD over the period 1979–2010 and relationships with heavy (85th percentile) precipitation in the Karakoram/western Himalaya (KH) and central Himalaya (CH) using multiple datasets. We show that heavy precipitation events occurring in the KH and CH are often spatiotemporally independent, suggesting differing behavior of WWD affecting each region. The wavelet power spectrum of 200 hPa geopotential height anomalies is used to characterize the frequency and magnitude of individual disturbances and to distinguish synoptic scale variability through time. Our analysis exhibits an enhancement in the strength and frequency of WWD in the KH and indicates an increase in local heavy precipitation events. In contrast, the CH is observed to experience weakening influence of these disturbances and consequently, a decrease in heavy precipitation. Furthermore, we investigate multi-annual variability of WWD and teleconnections with some known modes of climate variability affecting central Asia, including the Arctic Oscillation, Eurasian/Polar Pattern, the El Niño Southern Oscillation, and the Siberian High. Although there is clear evidence that these modes affect circulation and precipitation in High Mountain Asia, their competing influences on WWD are complex and non-linear. These results suggest that a thorough understanding of WWD and their spatiotemporal variations are crucial to improve our knowledge of the hydrologic cycle within High Mountain Asia as well as our ability to project the future status of Asia’s water resources.

Two extreme snowfall events associated with extratropical cyclones, one interacting with the western and one with the central Himalaya, are simulated with the Weather Research and Forecasting (WRF) model over 8 days. One event in January 1999 was driven by a longwave trough over west Asia, with the cyclone becoming terrain-locked in the western Himalayan notch. Another event in March 2006 was driven by a trough further south and east, facilitating the passage of two successive cyclones along the entire Himalayan ridge, drawing moisture from warm tropical waters. These flow patterns are typical for extreme winter precipitation in the western and central Himalaya, respectively, but were amplified in these two cases. In the WRF simulations, snowfall is confined to the western Himalaya in the January simulation, while a near-continuous band of accumulated snowfall along the Himalayan ridge forms in the March simulation. Precipitation rate throughout both simulations is largely determined by cross-barrier moisture flux, which is generally greatest wherever the cyclonic winds converge on the mountains at each time. However, the March 2006 simulation evolves in an environment with greater convective instability upwind of and moisture transport toward the mountains than in the January 1999 event. Hence, greater precipitation rates and more solid snowbands are generated in the March than in the January simulation. However, due to the terrain-locking of the cyclone in the January event, individual locations receive more persistent snowfall, so that the greatest 8 day accumulations are similar between the two events, although these accumulations are more widespread in the March event.