Abstract: Conventional ground-level meteorological observation data,NCEP (National Centers for Environmental Prediction) reanalysis and flux data were used to analyze the variations of visibility,wind,temperature,relative humidity,sounding and sensible heat flux during the whole process of a large-range dense fog during February 11-12,2016 over Jiangsu province.The results show that the precipitation on February 11 over Jiangsu area supplied sufficient vapor for the fog formation,and the temperature inversion layers,suitable surface wind speeds,and vertical wind shears favor the fog formation as well.Increase in humidity before the fog formation had a certain indication for the fog forecast,with a threshold of above 95% in winter.The temperatures at some stations had a slight increase at night in the event,which may be related to latent heat release due to vapor condensation.Ground-air temperature differences and sensible heat flux both appear negative,suggesting the ground cooling effect on the air.Clear sky radiative cooling at night was a direct cause of the event,whereas the temperature and humidity inversion layers caused by advection favored the advanced formation and maintaining of the fog.As far as most areas of Jiangsu province is concerned,this dense fog event was of radiation fog.From a forecast point of view,it is necessary to pay close attention to the establishment and maintaining of temperature inversion layer,and variations of the lower-level cloud cover at night ought to be considered as well if it rains during the daytime.