The maximum rainfall of 24 hours is known as one of the extreme indicators of rainfall that causes severe damages. In order to select the sample day for the heaviest rainfall at synoptic Yasuj station, daily rainfall data during the years 1986 to 2020 were obtained from the Meteorological Organization. Day 11th January 2004, with a maximum rainfall of 135 mm, was selected to investigate synoptic and identify circulation patterns. Examining the patterns showed that the integration of low pressure in the area of Africa, which had made its way from Sudan to the Arabian Peninsula and Iran, with the low pressure in Cyprus and the establishment of a wide front over the atmosphere of the region, along with being located in the right half of the western winds, led to the formation of this rain. It has become a limit. The required humidity has been transferred to the region by the high-pressure branch over the Arabian Sea and the Persian Gulf.