Satellite images for this afternoon show this nicely. Note the presence of shallow cumulus clouds over most of the higher mountains and plateaus of Utah, with fewer clouds over the valleys and basins. In a few places over the high terrain, the clouds are deeper and producing anvils. This is especially apparent in northeast Utah where some deeper clouds are found over the Uinta Mountains, whereas it is cloud free over the Uinta Basin to the south. The storms over the eastern Uinta Mountains might be producing some showers and maybe even a bolt or two of lightning.
This tendency for convective (cumulus) clouds and storms to form over the mountains occurs because the air is more strongly heated during the day over the slopes and higher terrain of mountains and plateaus than the atmosphere at comparable elevations more removed from the mountains. This leads to an thermally driven upslope flow with rising air and convergence that triggers cumulus clouds and thunderstorms over the mountains.
|Source: Houze (2012)|
There are other thermally driven flows that can contribute to cloud and thunderstorm formation. One example is the Great Salt Lake breeze, which is basically a sea breeze that forms because the air over the Great Salt Lake is heated less strongly than the surrounding land surface. Convergence at the leading edge of the Great Salt Lake breeze, sometimes called a lake-breeze front, can contribute to cloud and storm formation. In fact, it contributed to the development of the storm that spawned the August 11, 1999 tornado over Salt Lake City.
Of course, one needs to be cautious about over applying these generalizations. For example, there are situations, especially in big terrain (e.g., Himalayas and Andes) where the upslope flow initiates storms not over the highest terrain but over the lower mountain slopes and foothills.