Here we show the potential for dense fog monitoring using existing measurements from wireless communication systems. Communication networks widely deploy commercial microwave links across the terrain at ground level. Operating at frequencies of tens of gigahertz, they are affected by fog and are, practically, an existing, sensor network, spatially distributed worldwide, which can provide crucial information about fog concentration and visibility. The goal of this paper is to show the feasibility for fog identification and intensity estimation. A method is proposed and is demonstrated by two cases of heavy fog that took place in Israel. During these events, fog covered wide areas (tens of kilometers) and caused severe decrease in visibility, dropping as low as several tens of meters. Liquid water content and visibility values were estimated using measurements from tens of microwave links deployed in the observed area for each event. Each of the links provided a single measurement which was taken simultaneously across all of the links in the system. The values were found to be in the range of 0.5–0.8 gr/m3, high concentration values that match the maximum value range observed in field measurements carried out for prior studies in different test areas in the world. The visibility ranges calculated, between 30 and 70 m, fit the visibility assessments from the specialized measuring equipment operating in the observed area at the same time. These results point to the strong potential of the proposed technique.