the events of extremum rainfall in northeastern Iran during the last 20 years (2021-2000) have been studied using rainfall indexes. For this purpose, data from synoptic meteorological stations of Mashhad, Sabzevar, Quchan, Neishabour, Bojnourd and Gonbad Kavous were used and Atmospheric patterns leading to these extremum events and the trend of extreme indexes were investigated using linear regression. The results showed that in all stations studied, highest standard deviation for all extreme indices was related to Gonbad Kavous station, which indicates the higher probability of unconventional rainfall for this station. The highest frequency distribution index of number of very heavy precipitation days (R20mm) in the statistical period and in the seasonal period with 37.4% frequency belongs to winter and in the monthly period with 19.3% frequency belongs to March. Synoptic analysis of heavy rainfall in the northeastern region of the country, mean sea level pressure maps, geopotential elevation and wind field maps at 850 hPa, omega pattern at 700 hPa and specific moisture distribution pattern at 850 and 700 hPa were used. The results showed that the most important feature of large-scale patterns leading to extreme rainfall is their high persistence in the eastern part of the Mediterranean. These blocking patterns are accompanied by the deployment of a low pressure system on the ground and the middle and upper levels of troposphere, which includes rising speeds in the lower levels of troposphere and adequate moisture supply from sources from the Sea of Oman, the Red Sea and the Persian Gulf.