A two-station radiometer configuration, vertically separated by 185 m, allows the retrieval of fog liquid water path (LWP) and cloud optical depth of fog (COD f ) within an optimal estimation framework coupled with the Fu–Liou radiative transfer model. LWP is the only reliably retrieved parameter, whereas the effective radius (Reff) remains prior-dominated, because both broadband fluxes respond mainly to the LWP of the layer. A proof-of-concept evaluation against 28 tethered-balloon profiles from a three-day campaign gives a correlation of 0.71 and an RMSE of 5.4 g m−2 for LWP. The retrieval loses reliability for LWP > 30 g m−2 where the radiative signal saturates. The long-term observations (2020–2025) comprise 224 fog episodes (561 h), with autumn dominating (99 episodes, 295 h). Seasonal median LWP ranges from 19.1 to 23.5 g m−2 (19.4–26.9 g m−2 with a fourfold weaker prior) and the mean COD f stays near 3.1 ± 0.8, so the radiative impact of fog in the Strzy ˙zów Valley is controlled by the frequency of fog rather than by the COD f of individual events.