Fog phenomena are frequent natural hazards, sensitive to meteorological parameters, with significant impacts on visibility and transportation that may evolve under ongoing climate change. This study analyzes the spatial transformation and trends in fog properties in Poland from 1973 to 2020. The research utilises synoptic measurements from IMGW-PIB, the Integrated Surface Database, and long-term emissions data from the Peking University repository. To evaluate the influence of various factors on fog properties, a Random Forest Regressor model was employed. Results indicate regional variation in fog frequency, with higher occurrences (69–77 days/year) at certain stations (Zielona-Góra, Chojnice, Kielce) and lower frequencies in coastal areas (below 40 days/year). The duration of fog events ranges from 3.7 to 6.1 h/day, with visibility between 380 and 590 m. Trends in fog days shifted from a decline of 8.4 days/decade before 1990 to 4.4 days/decade afterwards. While central and northern Poland experienced a reduction in fog days pre-1990, an increase was observed in the southern regions. Post-1990, fog duration decreased significantly (−0.45 h/decade). Meteorological factors were found to influence fog occurrence strongly. Days with low wind speeds (< 3 m/s) showed a moderate correlation (0.47) with annual fog days, while mountainous regions and elevation had strong positive correlations (0.91 and 0.84, respectively). High humidity (100%) correlated moderately (0.42), whereas temperature exhibited a negative correlation (−0.78). The Random Forest model effectively predicted fog days, achieving an R² score of 0.64 for stations outside mountainous regions and 0.95 when including all stations, with minimal changes in the root mean square error (12 to 12.5 days/year).