On the features of clouds occurring over the Mackenzie River basin

[1] To better characterize the occurrence of clouds and some of their features over the Mackenzie basin of northwestern Canada, surface-based measurements of cloud fields have been examined from several operational observing sites. This article focuses on the determination of cloud cover fraction, cloud base height, multiple layering, and cloud type as well as the variations of these on temporal scales ranging from diurnal to interannual. In addition, the cloud features were related to the large-scale circulation, large-scale convergence, air mass, and surface temperature. The results indicate that clouds over this region are very common (occurring about 80% of the time and covering an average of about 60% of the sky), are linked with surface temperature variations (such as being less common and higher during winter cold periods), are poorly correlated with large-scale factors (such as El Nino), and may be exhibiting some long-term trends (such as an increase in cloud cover fraction).