Alberta  spans 11 degrees of latitude, and its varied topography includes elevations ranging from 170 meters (560 feet) above sea level in the extreme northeast to more than 3,700 meters (12,100 feet) above sea level along the Continental Divide. As a result, the climate of the province varies widely from place to place. In addition, the Canadian Rockies  create some of Alberta’s unique climatic characteristics. As prevailing, moisture-laden westerlies blow in from British Columbia , the cold heights of the Rockies wring them dry. This cycle makes for clear, sunny skies in southern Alberta; Calgary  gets up to 350 hours of sunshine in June alone, which is good news, unless you’re a farmer. In winter, the dry winds blasting down the eastern slopes of the Rockies can raise temperatures on the prairies by up to 40°C (104°F) in 24 hours. Called chinooks, these desiccating blows are a phenomenon unique to Alberta.
Another interesting phenomenon occurring in southern Alberta’s Rocky Mountain regions is the temperature inversion, in which a layer of warm air sits on top of a cold air mass. During these inversions, high- and low-country roles are reversed: Prairie residents can be shivering and bundling up while their mountain fellows are sunning themselves in shirtsleeves.
Overall, Alberta  features cold winters and short, hot summers. May to mid-September is ideal for touring, camping out, and seeing the sights; one month on either side of this peak period, and the weather is cooler but still pleasant; and the rest of the year the skiing and snowboarding are fantastic.
January is usually the coldest month, when Calgary ’s mean average temperature is –13°C (8.5°F) and Fort McMurray ’s is –20°C (–4°F). In winter, extended spells of –30°C (–22°F) are not uncommon anywhere in the province, and temperatures occasionally drop below –40°C (–40°F). Severe cold weather is often accompanied by sunshine; the cold is a dry cold, unlike the damp cold experienced in coastal regions. Cold temperatures and snow can continue until mid-March. Groundhog Day (February 2) is noted, but Albertans realize spring is still a long way off for them.
After the March 21 spring equinox, daylight exceeds nighttime, and the coldest days of winter become a distant memory. Although spring officially continues to late June, snow often falls in May, many mountain lakes may remain frozen until early June, and snow cover on higher mountain hiking trails may remain until late July. Late snowfalls, although not welcomed by golfers in Calgary, provide important moisture for crops.
Summer is officially June 21–September 21, the dates of the summer and fall solstice, respectively. Air temperatures lag behind solar intensity as the sun melts snow, heats land surfaces, and warms the water of lakes and rivers. July is the hottest month and provides the most uniform temperatures throughout the province. On hot days, the temperature hits 30°C (86°F)—usually every other summer day in the south—and occasionally climbs above 40°C (104°F). Again, because of the dry air, these high temperatures are more bearable here than in coastal regions experiencing the same temperatures. Alberta  records around 40 tornados each summer. The deadliest on record killed 27 people in Edmonton  on July 31, 1987, while a tornado that touched down in Pine Lake in 2000, killing 12, was the deadliest in North America that year.
The frost-free growing season is over by late September, when the air develops a distinct chill. October brings the highest temperature variations of the year, with the thermometer hitting 30°C (86°F) but also dipping as low as –20°C (–4°F). Mild weather can continue until early December, but the first snow generally falls in October, and by mid-November winter has set in.