The Investigation of Synoptic Patterns of Torrential Rains in Lorestan Province

Abstract The study of synoptic rainfall has been an important parameter in the study of Torrential Rainfall. Every year, rain induced floods cause a lot of financial and. economic losses in Lorestan province. These flood producing rains are the result of some special synoptic situations. From the meteorological maps of NCEP, the synoptic analyses of 24 major floods were studied. Results and The results of the study showed that on the ground and at the level of 500 hp, heavy rainfalls in Lorestan have originated four patterns. the first pattern: The blowing of Siberian high pressure to west and Combination with Assure high pressure, cold advection form east north to Iran, cold advection from European to north Africa which causes the transmit ion of moisture into Iran and the production of Sudan system, worm advection from Persian gulf by Arabian Subtropical high pressure to lorestan province. The second pattern: this is pattern shown that Siberian high pressure is vey empower and blowing to Iran and worm water in south Iran which causes worm and humidity advection to Iran and Sudan system and combination Sudan system, Mediterranean system with Island system. The thirty patterns: cold advection from high latitude by Island system and combination with low latitude systems. The forth pattern: combination Assure high pressure with European movement, The existence of a blocking system on the North of Europe which hinders the movement of the waves to the East and diverts the systems to lower latitudes, The existence of Arabian high altitude on the Oman sea and Persian Gulf which causes the transmission of hot and humid weather into Iran.