Abstract:

To further improve the forecast level of frontal fog, we analyzed the causes of a persistent large-scale frontal fog occurred in Guizhou from January 3-4, 2017 by using synoptic map data and hourly observation data from automatic stations. The results showed that: the southerly airflow transported vapor from the Bay of Bengal and the south China Sea to Guizhou and other places; the 850 hPa temperature trough carried cold advection invasion and the formation of ground stationary front, which provided favorable weather conditions for this frontal fog; the continuous convergence of water vapor over Guizhou resulted in the development and thickening of low clouds, the formation of heavy fog on the ground was due to the descent and grounding of cloud bottom; the stationary front retreated to the east and moved northward, the warm and wet air flow in the southwest passed through the cold advection region, which caused the fog to continue to develop; the inversion layer gradually weakened and disappeared, the cloud floor rose, the fog also weakened and dissipated; the convergence of low-level airflow and the divergence of middle level airflow were beneficial to the formation of fog. During the fog period, the water vapor saturation and wind speed were small, and the temperature in the early stage was decreasing and kept stable in the middle and late stages near surface layer, which was conducive to the formation and maintenance of the fog.

Key words: frontal fog, weather cause, stationary front, inversion layer, warm and moist airflow