ANALYSIS AND SYNOPTIC PATTERNS CLASSIFICATION OF SNOWFALL EVENTS IN GUILAN PROVINCE

In order to identify and classification of synoptic patterns of snowfall in Guilan province was used NCEP/NCAR reanalysis 1 database. For this purpose, 253 snowfall days from 1998 to 2018 (20 years) were determined and then 500 hPa geopotential level were used to classify patterns by PCA method. In this study, an environmental to circulation approach was used. The results of the data classification showed that four European high pressure patterns, bipolar blocking, Siberian and North Caspian Sea dynamic-thermal high pressure and Mediterranean cyclones control the area's snowfall days. In the first three patterns, the arrangement of the western wind waves and the amplification of the high pressure through the convergence of the air flow in the mid-atmosphere are considered to be obvious and the air subsidence in this level increases the vertical upward extend of high pressure to higher levels. Thus the above three high pressures and Mediterranean cyclones are also dynamic and this is one of the prominent features of synoptic patterns of snowfall days.