Synoptic analysis of heavy snowfall in mountain roads of central Zagros (Case study: road of chelgerd- shahrekord- lordegan)

The Central Zagros cold season with abundant snowfall that other event such as climate, influenced by the atmosphere circulation patterns and distribution of surface pressure of Earth. In this study, to determine weather patterns and dynamical conditions of heavy snowfall in the mountain roads, daily data of synoptic station: Borougen Branch, Koohrang and Lordegan for the year 1987- 2010 of Iran Meteorological Organization received. In the following, days of heavy snow to use of index measure rainfall more than 15 mm and below-freezing temperatures and check the monitor code 70-75 (Code scout snow), 136 days of heavy snow was determined. In order to determine weather patterns, principal component analysis matrix array S on 500 hPa geopotential height data was used. The results showed that heavy snowfall in the mountainous roads of Zagros cause to seven synoptic patterns. As trough of the east Mediterranean is west of Iran and study area is close to the region's extreme volatility. At the same time low pressure gradient in north and south of the study area Caucasus is severe, respectively, associated with strong positive vorticity in the study area, and strong negative vorticity on the East of Oman in the south and Caucasus area in north. However, low pressure center and the North East with strong positive vorticity and high pressure of Siberia to the eastern border of Iran is the continuation and sustainability under the dynamic conditions in the study area. During heavy snowfall strong high pressure of Siberia combined from the north of Iran and the Caspian Sea with high-pressure of Caucasus in relation to Polar vortex in the middle levels of the atmosphere Caucasus cold air streams in the study area. The humid currents from the Black Sea and the Mediterranean by the cyclone flow in the West of Iran through the Persian Gulf region flows to the Zagros Mountains. In all atmospheric patterns, the temperature of zero degrees in the south on the Persian Gulf region and the arrival of masses of cold and wet down to widths And heavy snowfall in the roof of Iran.