Diagnostic analysis of a regional heavy snowfall event over the Tibetan Plateau using NCEP reanalysis data and WRF

摘要

Snowstorms frequently occur in spring over the heterogeneous underlying surface of the Tibetan Plateau, causing both economic and societal damage. What the intensity of factors triggering snowstorms remains poorly understood. This study quantitatively diagnoses water vapor, the thermodynamic and dynamic conditions of a large-scale heavy snowfall event over the Tibetan Plateau using reanalysis data. Here we show, a cold vortex, the Southern Branch Trough and a meridional shear line are favorable synoptic systems. The snowfall is characterized by low-layer (- 8.3 x 10(-7) g s(-1) hPa(-1) cm(-2)) and whole-layer (- 4.5 x 10(-4) g s(-1) cm(-2)) moisture convergence, low-level atmospheric convergence and high-level divergence (+/- 3 x 10(-4) s(-1)), low-level positive vorticity (4.8 x 10(-4) s(-1)) and strong vertical velocity (- 4 Pa s(-1)). Although the convectively-stable stratification acted to suppress snowfall, the abundant water vapor and strong orographic uplift of Himalayas and the downhill wind speed convergence overcome this to trigger the heavy snowfall event witnessed in March 2017. These diagnostic results are well consistent with those from WRF simulation. Our study acknowledges the importance of WRF in diagnostic analysis, deepens the understanding of evolution mechanisms and provides theoretical references for accurate forecasting of such events over the Tibetan Plateau. It would aid the development of effective strategies for sustainable livestock, and the mitigation and prevention of snow disasters in this region.