Synoptic analysis of unexampled super-heavy rainfall on April 1, 2019, in west of Iran

The aim of this study is to analyze the synoptic and analyzing the mechanisms of flood occurrence on April 1, 2019, in the western half of Iran. In order to statistically analyze super-heavy precipitation in western Iran, the daily meteorological data from April 2019 for 13 synoptic stations in Kermanshah, Hamadan, and Lorestan Provinces were received and used by the Meteorological Organization. The results show that on the peak day of precipitation in the western half of the country, most stations recorded more than 100 mm of precipitation, the highest of which, 127 mm, occurred at Nahavand station. The arrangement of sea level pressure patterns also indicates the existence of severe pressure gradients between the low pressure in northern Saudi Arabia and western Iran and the high pressure of Siberian and European cold cores, which have created contradictory weather conditions and a strong front at sea level. Also, in the middle and upper levels of the troposphere, with the penetration of cold air flow and cyclonic from Russia and its settlement in West Asia and the region in the form of cutoff low-pressure blocking, severe positive vorticity and divergent and humid ascent flows at all analyzed levels in the western half of the country have been created. Humidity advection maps of 500–1000 hPa levels show that at the 850 and 1000 hPa levels a humidity supply is provided from various sources in the Gulf of Aden, Red Sea, and Mediterranean Sea. But at levels of 500 and 700 hPa, only the Mediterranean Sea plays a key role in supplying and injecting humidity.