The analysis of synoptic-dynamic of snowfall in Yazd Province

In the most areas of our country, especiallyin heights, the most common kind of precipitation is assnow that can be considered a main source of waterfor streams, springs, underground watersheds and Qanats. The heights ofYazd province is one of the snowy regions in ourcountry because of geographical situation and topographic conditions. The purposeof this research was to understand, examine and analyze synoptically-dynamically snowfall in Yazd Province. For this purpose, 12 snowfallcourses during the statistical period 1999-2011 were selected following theaccess to the required data and the identification of thegeographical situation in the region. Daily snow and rain dataand synoptic maps of surface level and upper levels ofatmosphere, jetstream, omega, vorticity and moisture, NCEP/NCA base wereused in order to identify air mass movement and studysynoptic systems in the province and the related maps wereplotted in GrADS environment. Three synoptic patterns were extracted afterconducting climatic thermodynamic researches affecting Yazd province and studying dynamiccharacteristics in terms of strengthening and weakening pressure systems. Inthe first pattern, low-pressure combinatory systems of eastern Mediterraneanand Sudanese lead to snowfall especially in Yazd province heights. This is accompanied with the eastern Mediterranean troughs and entranceof cold air from high pressures of high altitudes. Inthe second pattern, the emergence of the blocking phenomenon causessnowfall and severe cold in Yazd province. This phenomenon occursalong with deep troughs of eastern Mediterranean and Red sealeading to cold air and snowfall for several days. Inthe final pattern , the availability of Caspian and Siberian highpressures lead to cut-off low in the central andnorthern regions of Iran which in turn causes snowfall inthe central regions including Yazd province.