Abstract:  Based on the conventionally observational data and the NCEP reanalysis data from December 1 to 7, 2011, the synoptic background, temperature and humidity conditions, atmospheric stratification feature of a wide area of continuously heavy fog event in Shandong province were analyzed by a diagnosis analysis method. The results show that this event occurs under stable stratification, flat general circulation at high level and mid-latitude. There is a large scale of high pressure area from east Siberia to south China, and Shandong province is located in the middle of high pressure. The synoptic situation is stable. Top of fog image is smooth and there is a clear edge on the high resolution visible cloud image, while there is not distinct feature on the infrared cloud image. The weak east to northeast wind (wind speed is less than 2 m·s^-1) near the surface is favorable to advection transportation of warm and humid air flow from the ocean, and it is also favorable factors for the formation of colder underlying surface. Turbulence is vigorous in boundary layer that brings considerable vertical transportation of turbulence kinetic energy. There is a significantly inversion layer at low level in the initial period of the fog process. It is clear and radiative cooling is obvious, so the radiation fog is dominant at the early period. However, it is advection fog at the middle and late period because warm and humid air blows to colder underlying surface.

Key words: Heavy fog, Circulation pattern, Diagnostic analysis, Temperature advection