Abstract:

Using the conventional observation data and NCEP FNL reanalysis data, the causes of a failed forecast snowstorm process were analyzed in the Liaoning region in early 2016.The results show that there are frontogenesis activities in the heavy snowfall area, and the frontogenesis is the direct cause of the intensification of snowstorms.Continuous frontogenesis occurs during snowfall, and the total frontogenesis function develops higher with time.The positive contribution of the horizontal deformation term to frontogenesis is greater during the heavy snowfall stage, especially when the contribution of elongation deformation to the horizontal deformation term is significant.The northeast wind in the eastern Liaoning provice and the easterly wind in the northern Yellow Sea both pass through the θ_se line, and the two air currents converge to form a narrow band with more dense θ_se contour lines.The clear contrast of temperature and humidity in this area produces frontogenesis.Under frontogenesis, the secondary circulation of the front is conducive to the development and maintenance of the upward movement, and the dynamic lifting and the enhancement of water vapor convergence lead to heavy snowfall weather.The frontogenesis caused by the enhancement of elongation deformation in the forecast is easy to ignore, which is the main cause of the snowfall forecast error.Therefore, the snowfall amount in the corresponding region can be revised to reduce the forecast error.

Key words: Snowstorm, Frontogenesis, Horizontal deformation term, Elongation and deformation, Forecast deviation