section_path: Geography/Climate
section_name: Climate
paragraph_text: Climate
  
  Most of Tehran has a cold semi-arid climate, BSk within the Köppen climate classification. The climate is BSh (hot semi-arid) around Mehrabad International Airport and cold semi-arid in higher areas, with a borderline Mediterranean climate (Csa) in the northern area of Tehran, with hot, dry summers and cool, rainy winters. Tehran's climate is largely defined by its geographic location, with the towering Alborz mountains to its north and Iran's central desert to the south.
  
  There are significant differences in elevation among various districts, and the weather is often cooler in the hilly north than in the flat southern part of Tehran. For instance, the 17.3 km (10.7 mi) Valiasr Street runs from Tehran's railway station at 1,117 m (3,665 ft) elevation above sea level in Tehran's south, to Tajrish Square at 1712.6 m (5612.3 ft) elevation above sea level in the north. The elevation rises up to 2,000 m (6,600 ft) at the end of Velenjak in northern Tehran. The sparse texture, the existence of old gardens, orchards, green spaces along the highways and the lack of industrial activities in the north of Tehran make the air in the northern areas 2 to 3 degrees Celsius cooler than the southern areas. Air currents have a great effect on Tehran's weather. The prevailing wind blowing from the west causes the west of Tehran to always be exposed to fresh air. Although this wind brings smoke and pollution from the western industrial areas, its strong wind takes polluted air out of Tehran.
  
  The main direction of the prevailing wind is northwest to southeast. Other air currents that blow in the area are:
  
  Most of the annual precipitation occurs from late autumn to mid-spring. March is the wettest month with an average precipitation of 39.6 mm (1.56 in). Summer is the least rainy season, and September is the driest month of the year. The average annual rainfall is sometimes very different in the north and south regions. One of the most intense rains happened on 21 April 1962, with 10 hours of rain. Meteorology determined that the amount of rainfall on that one day was equivalent to six years. The hottest month is July, with a mean minimum temperature of 24 °C (75 °F) and a mean maximum temperature of 36.7 °C (98.1 °F). The coldest is January, with a mean minimum temperature of −0.4 °C (31.3 °F) and a mean maximum temperature of 7.9 °C (46.2 °F). There are between 205 and 213 days of clear to partly cloudy weather.
  
  Summer is hot and dry with little rain, and relative humidity is generally low. Average high temperatures are between 31 °C (88 °F) and 38 °C (100 °F) during summer months, and it can sometimes rise up to 40 °C (104 °F) during heat waves. Average low temperatures in summer are between 18 °C (64 °F) and 25 °C (77 °F). It can occasionally drop to below 14 °C (57 °F) in the mountainous north of the city at night. Winter is cold and occasionally snowy, with an average of 12.3 snow days annually in central Tehran and 23.7 snow days annually in northern Tehran. During the winter months, average high temperatures are between 3 °C (37 °F) and 11 °C (52 °F). Average low temperatures are between −5 °C (23 °F) and 1 °C (34 °F), and it can occasionally drop to below −10 °C (14 °F) during cold waves.
  
  The highest recorded temperature was 43 °C (109 °F) on 3 July 1958. The lowest recorded temperature was −15 °C (5 °F) on 8 January 1969.
  
  In February 2005, heavy snow covered all parts of Tehran. Snow depth was recorded as 15 cm (6 in) in the south and 100 cm (39 in) in the north. One newspaper reported that it had been the worst weather in 34 years. Ten thousand bulldozers and 13,000 municipal workers were deployed to keep the main roads open. On 5 and 6 January 2008, a wave of heavy snow and low temperatures covered Tehran in a thick layer of snow and ice, forcing the Council of Ministers to declare a state of emergency and close down the capital from 6 January to 7 January. On 3 February 2014, Tehran received heavy snowfall, specifically in the northern parts of the city, with a depth of 2 metres (6.6 ft). In one week of successive snowfalls, roads were made impassable in some areas, with the temperature ranging from −8 °C (18 °F) to −16 °C (3 °F). On 3 June 2014, a severe thunderstorm with powerful microbursts created a haboob, engulfing Tehran in sand and dust and causing five deaths, with more than 57 injured. This event knocked down numerous trees and power lines. It struck between 5:00 and 6:00 p.m., dropping temperatures from 33 °C (91 °F) to 19 °C (66 °F) within an hour. The dramatic temperature drop was accompanied by wind gusts reaching nearly 118 km/h (73 mph).