Christchurch has a dry, temperate climate, with mean daily maximum air temperatures of 22.5 �C (72 �F) in January and 11.3 �C (52 �F) in July. Under the K�ppen climate classification, Christchurch has an oceanic climate (Cfb). The summer climate is often moderated by asea breeze from the Northeast, but a record temperature of 41.6 �C (107 �F) was reached in February 1973. A notable feature of the weather is the nor'wester, a hot f�hn wind that occasionally reaches storm force, causing widespread minor damage to property.
In winter it is common for the temperature to fall below 0 �C (32 �F) at night. There are on average 70 days of ground frost per year. Snow falls occur on average once or twice a year in the hill suburbs and about once or twice every two years on the plain, about half as much.
On cold winter nights, the surrounding hills, clear skies, and frosty calm conditions often combine to form a stable inversion layer above the city that traps vehicle exhausts and smoke from domestic fires to cause smog. While not as bad as smog in Los Angeles or Mexico City, Christchurch smog has often exceeded World Health Organisation recommendations for air pollution. The city has funding available to upgrade domestic home heating systems, and to limit air pollution has banned the use of open fires as of 1 January 2006. As of 2008, wood burners more than 15 years old are prohibited
