Seyedeh Ameneh Sajjadi - The member of scientific research board of Islamic Azad university (Rashtanch)
sadeghi-Hoseini - Geophisic Institute Tehran university of Iran
Soheila Javanmard - Atmospheric science and Meteorological research center,
Parviz Irannejad - Geophisic Institute Tehran university

One of the most important disaster in the west of Iran, Particularly in cold season is flood. The precipitation in the west regions is longer while tropical systems are predominant . In this research we studied this percipitation w hich is accompany with convective instability . one long precipitation period (1994) in the cold season of ltermanshah (47" 04'N-34'18'44 B) were selected to study.Maps:surface 500 & 300 hectopascal levels , upper atmosphere of kermanshah zone & skew-T diagrams at (1200UTC) hour were applied for synoptical analysis. Thermodynamical indexes mixing ratio,Potential temperature and instability of Atmosphere (Showalter index,K index,Convective Available Potential Energy)and perticiable water were studied and It As a result west systems, in these periods ,accompany with a meditteranian low pressure system on the earth surface and upper atmosphere Trouph and supplied enough moisture have suitable pattern for precipitation that . In this region the wind speed is at maximum which can be identifical from maps 30 hectopascal 1evels.With calculation above factors we can opine about torrential rain in the west of Iran.

Synoptic Climatology,Flood, Precipitable water, Istability Indexes, kernshah