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This study was conducted in order to determine the situation and position of Jetstream in the west of Iran and its speed during the rainy synoptic systems in land surface. Therefore, rainfall data of sven synoptic stations in Ilam and Kermanshah provinces during the 1990s, and 60 systems were selected and of the accessible systems the maps 54 were analyzed. The required analyses were carried out by assessing maps on two days before precipitation, beginning of the precipitation day and the days of maximum precipitation. The results showed that Jetstream tracks had anticyclonic curve two days before precipitation which acquire cyclonic curve on the beginning of of precipitation day and the days of maximum precipitation. The value of the Jetstreams meridian gradient is much more, on the days of maximum precipitation than the other days and falls to the minimum rate on the days before precipitation. Jetstream cores were spread on two days before precipitation too which were concentrated in two areas on the beginning and on the maximum precipitation days. The first area was placed in 25-30° north latitude and 32.5-42.5° east longitude (Northern Red Sea) and the second area in 35-39° north latitude and 45-50° north longitude (Southeastern Caspian Sea). There was no linear correlation between Jetstream cores velocity and the volume of system precipitation, because of the effect of many factors on the amount of the systems, precipitation amount. The maximum effect of Jetstream in the studied area was when the Jetstream in the upper levels of troposphere (200 hp) was place of in the south of the lower levels of the Jetstream (300 hp), so that the Jetstream in the lower levels of troposphere was closer to the studied area.

Keywords: Climatology, Synoptic, Jetstream, Ilam, Kermanshah.

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