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  Extreme precipitation is one of the climatic risky behaviors that are associated with abnormalities and environmental-human consequences. This study has investigated daily rainfall  of 20 rain gauge and synoptic stations over 30 years (1987-2016) in the West of Gilan province, to determine the trend of extreme precipitation changes. In this regard, non-parametric Mann-Kendall test, Sen's Estimator slope, Poisson distribution, and IDW interpolation have been applied, respectively, to determine the existence of trend, significance, to determine the probability of rainfall occurrence   and to identify spatial patterns of precipitation occurrence with different probabilities. The results suggested an increasing trend in Astaneh-ye Ashrafiyeh, Bandar-e Anzali, Masuleh, and Astara and an extreme decreasing trend in Bash Mahalleh due to the Mann-Kendall test. Studying the significance or insignificance of changes trend by Sen indicated that this trend has been significant in Mashin khaneh, Bash Mahalleh, and Punel Stations; and the null hypothesis, that is, the insignificance of change, was rejected. Sen's Method revealed that there were no significant changes in other stations, and their randomization will be confirmed. To this end, the spatial probability distribution of  to  indicate kernel probability displacement for different x.  The maximum probability to various occurrences has been at Masuleh station and Poisson distribution is a proper assessment of precipitation in this region.
 

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   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.