Statistical and synoptical analyses of fog event in Rasht International Airport

To better understand of fog events in the Rasht Airport, to improve the forecast accuracy, some statistical and synoptical analyses studied by 800m and less horizontal visibility during years 2000-2009. In this research, some parameters such as horizontal visibility, temperature, dew point deficit, relative moisture and winds speed on onset hour and in the duration of the event have been analyzed. Frequency percent of fog events was calculated for all month during 2000-2009. Frequency of occurrence increases in the colder months especially in February is about 24.64 .The occurrence frequency of long duration fog events that begin between 1800 UTC to 2100 UTC hour is more than 2100 UTC to 0300 UTC hour; and the most fog events terminate nearby sunrise. The horizontal visibility at the onset time was lower (100m) for long duration fog events. In the most events, dew point deficit and relative humidity at the fog onset time were calculated zero and 80% respectively. Low wind speeds (0-0.2 ms-1) have long been known to favor fog development. Studied on Synoptic fog eventsshows that the most important patterns in long duration fog events development are blocking pattern, Col region and inversion in cold season.