Climatology and trends in some adverse and fair weather conditions in Canada, 1953–2004

This study characterizes the climatology and trends of some adverse and fair weather occurrence in Canada, on the basis of reliable long‐term records of hourly weather and bright sunshine observations at about 90 Canadian stations for the period 1953–2004. The results show that fair or no‐weather (i.e., no precipitation or visibility obscuration) trends are generally consistent with the sunshine trends, showing significant increases in southern Canada, with decreases in the Canadian Arctic. The increase of no‐weather is most extensive in spring and summer, while the decrease is most extensive in autumn. For the same period, freezing precipitation has become more frequent in the region north of 50°N (especially in spring and autumn) but less frequent in southern British Columbia (BC), central Prairies, and the Great Lakes area in autumn‐winter, as well as in northeastern Canada in winter. Blowing snow occurrence has decreased significantly almost everywhere across Canada, with the most significant decline in southwestern Canada in winter. In every season, fog occurrence has significantly increased in the Prairies‐Yukon‐Northwest Territories and northern BC but decreased in eastern Canada and southern BC. The frequency of low ceiling conditions (<304.8 m, i.e., 1000 feet) has increased in Alberta‐BC interior and the Great Lakes area, with the most significant increases in Alberta‐BC interior in autumn‐winter and in the Great Lakes area in spring; while the other regions have experienced a negative trend, which prevails across the country in summer.