Abstract: A regional snowstorm occurred over northern slope of the central Tianshan Mountains on March 16, 2011. The climatic background, circulation situation and physical diagnostic analysis of this snowstorm were conducted using the NCEP data, Micaps data and observed data on northern slope of the central Tianshan Mountains during the period from 1981 to 2010. The results showed that the 500 hPa circulation situation of the snowstorm happened was the convergence pattern of north and south frontal zones. When the snowstorm occurred, there was the sufficient water vapor supply and strong water vapor convergence, which was validated by the water vapor flux and divergence of water vapor flux field. The cold and warm cloud clusters joined up over the central Tianshan Mountains, which could be seen clearly from the infrared cloud image. The southwesterly warm-humid air along the Arabia Sea and the Bay of Bengal formed water vapor transport belt that provided plentiful water vapor for the snowstorm. Physical diagnosis revealed that both convergence area of ageostrophic wet Q-vector from 600 hPa to 400 hPa and the strongest frontogenesis were accorded with snowfall area. This finding may be of very importance in predicting snowfall intensity. The unstable stratification was intensified by the advection of positive differential pseudo-equivalent potential temperature. Thermal forcing also enhanced the development of ascending motion and was favorable for the intensification of heavy snowfall.

Key words: snowstorm, climate warming, circulation situation, physical quantity field, wet Q-vector, northern slope, central Tianshan Mountains