I work on 54th floor of a downtown skyscraper and I see clouds sometimes forming over the tops of high buildings in the Loop. How does this happen?
Clouds form over downtown high-rise buildings in the same way that orographic (mountain induced) clouds do: When easterly winds are blowing here in Chicago, temperatures tend to be cool in the moist marine layer. Buildings obstruct air flow just as mountains do so winds are forced to flow over or around them.
The atmosphere cools with height. In situations in which the air is moist but not quite saturated, forcing air to ascend over tall buildings can be just enough to cool the air to saturation and initiate cloud development. It’s a spectacular demonstration of man-made weather.