Based on the observation data provided by the automatic meteorological stations for road weather information in Beijing, the characteristics of low visibility thick fogs and the method of nowcasting are studied. The main conclusions are as follows: (1) The thick fog with the visibility below 200 m happens mostly between 05:00 to 09:00, from September to December, and lest between 12:00 to 18:00, from June and July. (2) About 80 % of thick fog cases with visibility below 200 m appears in Daxing and Tongzhou districts in the southeastern Beijing, and seldom in downtown. (3) Before the formation of thick fogs, there was a thick thin thick fluctuating pattern in visibility variation. (4) The visibility changes with the wind, temperature, and relative humidity; the south and east wind is advantageous to the formation of thick fogs; the northwest wind is advantageous to their dissipation. During the development period of thick fogs, wind speed becomes slow; relative humidity rises; temperature reduces; and visibility becomes lower. During the maintain period, the wind speed, relative humidity, temperature, and visibility all change slightly. During its dissipation period of, the wind speed becomes big; relative humidity reduces; temperature rises; and visibility becomes bigger; but the reduction of relative humidity is later than the rise of visibility.