Analyzing the effect of blocking system in creating heavy precipitations

To analysis the mechanisms of blocking high effects on heavy precipitations in northwest of Iran، we selected a short period of heavy precipitation (25-28 October 2008). In this case، weather maps such as mean of sea level pressure، 850-hpa and 500-hpa geopotential height levels were assessed and analyzed for the whole period. The position and movement of the atmospheric systems such as cyclones، anticyclones، fronts and wind fields were identified using the weather maps. Daily precipitations data were retrieved from Islamic Republic of Iran Meteorological Organization (IRIMO)، for 50 stations in the studied area that covered 12 provinces، and then were analyzed. The results indicated that a blocking system had been existed over the west of studied area in the whole time with two ridges that extended in its own sides. Wind field of lower levels (850-hpa) have had an important role in the humidity feeding of atmospheric systems which during the activity of the system has become the suitable pattern of the wind field in lower levels and provided a remarkable humidity feeding for the studied region. In addition، regionalization results of 24-hour precipitation amounts showed that during this period، the northeast parts of the region received more precipitation than other parts.