Analysis of Synoptic Systems Creating Heavy Precipitation during Cold Period of Year in Khorasan Razavi and Khorasan Shomali Provinces

The presented study aims to investigate synoptic atmospheric conditions along with heavy precipitation in Khorasan Razavi and Khorasan Shomali provinces. The identification of temporal and spatial distribution of heavy precipitation associated with these extreme conditions is another goal of this study. The amount of precipitation greater than 20 mm was chose to distinguish heavy rainfall from others. The parameters such as sea level pressure, temperature, relative humidity, specific humidity at the level of 700 hPa and wind direction were analyzed to identify sources of heavy precipitation moisture. Geopotential height at the level of 500 hPa was considered to determine heavy precipitation synoptic patterns. Wind speed and direction at the level of 300 HPA were evaluated to track the high-speed wind (jet stream). Then, these parameters were averaged monthly to investigate the general behavior of the atmosphere status associated with heavy precipitation in the studied area. The results show that in cold period of year the foci of heavy precipitation are located in Khorasan Razavi County. Mediterranean deep trough and Red Sea were identified as synoptic pattern and the main moisture source of heavy precipitation, respectively. Subtropical jet stream also recognized along with almost all heavy precipitation cases at level of 300 hPa.