Numerical model of fog formation is constructed based on the equations of inflow of heat and water vapor in the turbulent atmosphere, which are written in an invariant form. Turbulent and vertical motions are of basic importance in the transport of heat and water vapor from the Earth's surface to the atmosphere and within it. Interchange parameters are determined based on the similarity theory, and the vertical velocity parameters are determined from the continuity equation. According to observations, most frequently the fogs are formed in the areas of decreased pressure [V.A. Lukin, Analysis of Fog Formation in the South-West of Leningrad Region (VVV AIU, Voronezh, 1996), issue 18, 411 pp.]. As the characteristics of a synoptic situation (baric field) we use: the geostrophic wind (uniquely connected with the cyclone depth), the wind velocity and its deviation from an isobar near the Earth's surface (at the level of 10 m), the dimension (radius) of a cyclone, the thermal stratification, the shape (roughness) of the Earth's surface, the temperature, and the relative humidity in the initial state. Effect of these characteristics on the thickness and water content of fog, possibility of its formation are estimated quantitatively.