A Survey on Synoptic Patterns of Heavy SummerRain happening in the northern areas of Khorasan

In order to investigate and analyze the synoptic patterns in relation to heavysummer rain happening in the northern areas of Khorasan Province during 2001-2002,the earth surface pressure maps and the 500 mb ones were examined .The most significant patterns that were in coordination with the real flood happeningwere as follows:High pressure of the Caspian Sea, the higher atmosphere level trough, Kavir plainlow pressure, combination of polar and subtropical jet stream. Out of 18 cases understudy, 44.4 % including 8 cases, were about high pressure of the Caspian Sea andnorth flows over this sea, 27.7% including 5 cases, were concerned with higheratmosphere level trough, 11.1% including 2 cases, were related to Kavir plain lowpressure, and 16.2% including 3 cases, were due to a combination of polar andsubtropical jet stream .The patterns related to high pressure of the Caspian Sea and Kavir plain lowpressure have happened in the hottest summer days and higher atmosphere leveltrough with a combination of polar and subtropical jet stream occurred in spring .