Frequency analysis of snowfall in Iran over the past decades

In order to investigate the frequency of snowfall in Iran over the past decades and its relation with temperature, the data of hourly air, dry temperature and dew point temperature were used at 304 synoptic stations during the period of 1951-2010. First, from of 100 current weather codes, 6 snowfall codes were extracted and the time series, temperature, dew point and percentage of snow codes were calculated, and the temperature conditions of the dew point and the temperature of the dew point were considered for snowfall for each code.
The results showed that snowfall in Iran is a very low frequency and includes less than 2% of the present air. On the other hand, shower snowfall and extreme snow are not common, and most of the snowfall is mild to moderate. In terms of time, snowing is possible in Iran from November to the beginning of the April, but most snow events occurred in the months of January and February. There is a possibility of snow falling throughout the day and night, but the highest frequency of snow occurs in the early hours of the day, especially between 6:00 to 10:00. In general, the frequency distribution of snowfall in Iran has a negative skewness and its axis of symmetry is around zero degrees Celsius. So that the best ground temperature conditions for snowfall are around zero degrees, especially in the temperature range of 1 to 5 degrees Celsius.