The aim of this study is to determine the influence of atmospheric circulation on the extreme cold days in Iran. The mean daily air temperature data from 663 weather stations in Iran during 21/03/1961 to 19/03/2004(15705 day) were used. The temperatures data of 663 stations were interpolated by Kriging method for 18*18 Km pixels. A matrix was obtained (15705*5214). Data of sea level pressure were collected from NCEP/NCAR, affiliates of National Centers for Environmental Prediction and The National Center for Atmospheric Research of the United States. In this study an extreme cold temperature event is defined by Normalized Temperature Difference (NTD) index. Then, the data were ordered according to the size and extremeness of cold events. First 500 coldest and the most pervasive days were selected as the sample. In the sample days, anomaly of sea level pressure was calculated. The results showed that the coldest and the most pervasive cold occurrences in Iran are accompanying with 4 patterns of sea level pressure anomaly.
