Mean July daily temperature

The map shows the mean daily temperatures based on the 30-year period 1941-1970 for the warmest month in Canada. Although, the most direct and the most intense incoming solar radiation occurs in June, there is a lag in the warming of the Earth’s surface. As a result the warmest month in Canada is normally July. The lowest mean July temperatures are below 5 degrees Celsius and are located in the Arctic Islands. The highest mean July daily temperatures are above 20 degrees Celsius and are located in southern Ontario, southern Quebec, south of Winnipeg, Manitoba, the Medicine Hat area of Alberta and in some valleys in the interior of British Columbia. Generally, the mean increases from north to south, from 2.5 to 22.5 degrees Celsius. In British Columbia, the warmer temperatures are in river basins of the Cordillera. In fact, all valleys of the Cordillera are warmer than the surrounding slopes. In winter, however, atmospheric inversions may result in valleys being warmer or colder than higher terrain. The warmest temperatures occur in the lower broader valleys of southern British Columbia, such as the Okanagan. This "warm valley" effect is less spectacular elsewhere in Canada, but may be observed, for instance, in the basin of the Red River of Manitoba or the Saguenay of Quebec. A steep temperature gradient along the shores of large bodies of cold water is also observed on this map. Earlier maps, based on 1931-60 data, showed a very generalized temperature pattern for July. The authors of the present map were able to refer to data from new stations and a longer record from existing stations. In constructing this map, recognition was given to the effect of the cold waters of the Arctic, deep lakes, and Hudson Bay. For instance, throughout most of July ice floes drift to and remain in south eastern Hudson Bay. Temperatures over such cold waters contrast sharply with those over heated adjacent landmasses and result in strong temperature gradients near the shorelines. Temperatures at shoreline stations, such as Churchill, can change as much as 10 to 15 degrees Celsius in a few hours when the wind shifts from offshore to onshore. Where the climate is suitable for vegetation, coastal areas having these extreme temperature differences exhibit marked changes in vegetation.