Extreme cold temperature events are among the natural characteristics of climate that occur annually and cause numerous problems in agricultural, industrial, and economic sectors, as well as road-related hazards. A sharp decrease in temperature can adversely affect various aspects of human life and activities, as well as the ecological conditions of plants.

The aim of this study is to investigate the synoptic atmospheric patterns influencing extreme cold waves in northwestern Iran. For this purpose, daily minimum temperature data from 36 synoptic stations in northwestern Iran were used over the period 1986–2017 for the months of January, February, March, April, November, and December. Using the standardized cold day index, days with intensity lower than −1.2 were identified as extreme cold days on a monthly basis for each station.

By applying factor analysis to sea-level pressure data corresponding to extreme cold days, four dominant patterns affecting the formation of cold waves in northwestern Iran were extracted as representative patterns. Synoptic analysis of these patterns indicates that the dominant synoptic systems responsible for extreme cold waves include the Siberian High, migratory European high-pressure systems, or their ridges at sea level over the northwestern region of Iran, which lead to the advection of cold air from higher northern latitudes toward the region.

orthwestern Iran.