Abstract: The weather process of a snowstorm event in the southwest region of the Tibetan Plateau on January 17 to 19,2013 was comprehensively analyzed using the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data with resolution of 2.5°×2.5°,conventional meteorological data and satellite cloud images in this study.The results show that the circulation situation during the snowstorm event in the southwest region of the Tibet Plateau is characterized by two troughs and two ridges at the middle and higher latitudes.The deep southern branch trough,southwesterly jet stream,and the Western Pacific subtropical high are the main influencing systems of the snowstorm event.The cyclonic vorticity reaches 15.0×10^-5 s^-1 during the snowstorm event,and the convergence at lower levels and divergence at middle and higher levels favor the ascending motion of the air.The positive divergence near 250 hPa is 3.5×10^-5 s^-1,and the powerful suction effect at middleand higher levels and the strong ascending motion play important roles in the snowstorm occurrence.Water vapor mainly comes from the Arabian Sea,and the increasing water vapor flux and its moving northeastwards divergence center indicate that water vapor is transported continually by warm and humid southwesterly flows and converges over the snowstorm area.Meanwhile,the orographic uplifting effect is favorable for the condensation of water vapor.The temperature of black body (TBB) obviously decreases when the clouds reach over the Tibet Plateau.TBB drops below -50℃ when clouds reach over the snowstorm area,and it is even lower than-60℃ over the Burang area in the western Tibet Plateau.

Key words: Tibet Plateau, Snowstorm, Southern branch trough, Black Body Temperature (TBB), Diagnostic analysis