Thermodynamic and Synoptic Analysis of exceptional rains of spring and role of cloud height in occurrence of rains in Shiraz

Mechanism, spring rains, mainly due to convective processes, the occurrence of rains and other climatic phenomena, such as the phenomenon as cut-off low provides conditions for heavy precipitation events. In this research first heavy rains of spring (rains of 30 mm with the highest total precipitation in the period 1335-1391) studied the city and two of the strongest of them were identified. To analyze these rains, we investigate instability indexes and sea level pressure, 500 hPa, Uwind, Vwind, omega and data of cloud height. The result show that main factor of heavy rains in the region is trough of east Mediterranean in the middle troposphere cut-off low phenomenon is well established, Therefore in both cases west instability systems change their ways to lower latitude so that the west systems get high level of humidity from southern warm water and make heavy rains in the region is significant. Also results instability indexes show that there is instability probability, the amount Omega negative and positive vorticity show severe Ascending movement in time is the occurrence of precipitation; but with investigation relation within thickness of cloud and heavy rains show thickness of clouds have increased.