Mist and fog observed at the Meteorological Station of the Institute of Astronomy, Geophysics and Atmospheric Sciences of the University of São Paulo (EM/IAG) in the southeastern part of São Paulo city in the winter of 2007 were classified according to its formation processes: advection or radiation. Meteorological data from EM/IAG, Congonhas Airport and reanalysis from the European Center for Medium-Range Weather Forecast, as well as radiosondes from Campo de Marte Airport were used. In the 1981-2015 climatology, it was observed that these phenomena are more frequent in the winter, with an average of 11 events per month. For the winter of 2007, 21 advection and 28 radiation events were detected, with radiation fog occurring more frequently in June (13) and advection fog, in August (12). The South Atlantic Subtropical High favored the formation of radiation events in 24 cases; 15 of which had the contribution of humidity advected by the sea breeze. Post-frontal anticyclone was associated with the remaining 25 cases, of which 15 were classified as advection. Four cases were chosen for a more detailed analysis. On July 2, 2007, radiation mist occurred, with the injection of moisture by the sea breeze; the next day, there was also radiation mist, however, with no sea breeze. On the 20th of July, fog was caused by advection of humidity with north/northeast winds coming from the Serra da Cantareira and on the 27th, advection mist developed due to the intensification of winds associated with the movement of a post-frontal anticyclone.