عنوان مقاله [English]
From a meteorological point of view, frost occurs when minimum daily temperature decreases to 0 °C. This study seeks to predict and rout early autumn frosts in Khash city. To study early frosts, the first day of frost in the statistical period of 1986 to 2008 was investigated. Probabilities and return periods of autumn frosts (early frosts) were estimated using normal distribution and Log Pearson type 3 distribution. In Log Pearson type 3 distribution, there is 99 percent probability that frost does not begin before 8 October, 95 percent probability that frost does not begin before 15 October. In normal distribution, there is 95 percent probability that frost does not begin before 12 October. Coefficient of data change is 21.2 which indicates relatively high frequency in the time of frost. A graph of the first day of frost and its 11 year average was prepared and frost occurring process was routed. Results indicate that during the last decades frost has retreated toward winter.