The synoptic investigation of flood in North Khorasan province

Floods are included in the natural hazards that can have devastating effects on human and the environment. North Khorasan province is one of the most flood-prone provinces in the country due to its topographic and geographical location and suffers damages from this natural disaster every year. This article deals with the synoptic study of a flood that occurred in the province using the analysis of land surface maps as well as 850 and 500 hPa pressure levels. The daily precipitation data from several synoptic stations in provinces affected by the selected systems were obtained from Iranian Meteorological Organization. The required data was extracted from the NCEP / NCAR archive on a regular network limited to zero to eighty degrees’ east longitude and ten to sixty degrees’ north latitude. Synoptic analyzes showed that crossing pressure patterns, over northeast of Iran can provide conditions for extreme weather events spatially gust fronts and sever convective rainfall in the region. High relative humidity and intense vertical velocity in the lower and middle levels of the troposphere are the main factors affecting heavy convective rainfall in the region; the former was due to the humid and warm southerlies winds at the surface and the latter was due to the cyclonic relative vorticity advection in the middle level troposphere.