Fog Climatology and Optimal Meteorological Conditions for Fog Formation at Yanbu International Airport, Saudi Arabia: A 21-Year Assessment

Fog is a low-visibility hazard in hyper-arid coastal environments. This study investigates the climatology, temporal variability, associated meteorological conditions, and predictability of fog at Yanbu International Airport, Saudi Arabia, using hourly METAR observations, Terminal Aerodrome Forecasts (TAFs) and ERA5 reanalysis during the period of 2005–2025. Fog showed seasonal and diurnal variability, with an autumn maximum in October and a peak around 0700 LT. Annual fog frequency and maximum duration exhibited interannual variability but no statistically significant long-term trends. Fog occurrence was associated with high relative humidity (≥94%), small dew point deficits (0–1 °C), and calm to light easterly winds (0–2 m/s), whereas mean sea level pressure (MSLP) played a secondary role. ERA5 vertical-profile analysis identified temperature inversions during 55.0% (94/171) of observed fog hours, indicating lower-atmospheric stability. ERA5 composites for 90 distinct fog events showed persistent moist conditions over the Red Sea and adjacent coastal region from −12 h through fog onset, with the strongest moisture availability and horizontal transport concentrated at 1000–975 hPa and progressively weaker signals at 950–925 hPa. TAF verification indicated limited forecast skill under the simplified daily-event framework. These findings establish a long-term climatological baseline and provide evidence of the thermodynamic and moisture conditions associated with fog formation in this hyper-arid coastal environment.