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Synoptic climatology is a science that studies the regulation of atmospheric phenomena and their changes, with the purpose of the prediction of climatic conditions.The main role of synoptic climatology is the identification of the dominant climate characteristics of the earth during mounths or seasons. Snow is one of the climate Phenomenon that by happening of it other factors would  be appear . In mountainous areas heavy snow create  many problems such as making blocke of public places, traffic and road accidents, severe frost and ... so this makes many  serious problem with relation public health and welfare  of the community and led to much annual economically and socially cost from the community imposes.The study region is located on the west of Iran from 37º.4' to 39º.42' N latitudes and 47º.3' to 48º.55' E latitudes. In this thesis, to realize that  synoptic reasons of  the regim of heavy snow precipitation in Ardabil region and its trends in terms of time, two method is used: statistical and synoptic.Thus in order to analyze statistically, in twenty years (1990 2009) the number of days with heavy snow  is used, and for synoptic analysis, has used ,synoptic maps of the surface and 500  hpa levels, which have received from the climatic center website called NOAA. On this basis, synoptic analysis showed that dominant position of effective pressure system including western trough and cold and warm fronts during snowy days. So we found many unities between Mediterranean and red sea lows during heavy snowy days.  And also statistical researches shows that the trend of yearly changes of  heavy snow precipitation days in Ardabil station is decrease.

Key words: statistical analysis , Synoptic analysis Ardabil region , heavy snow- low pressurs