What would prevent an orbiting ship from scanning a planet?

In Star Trek a common plot device was for electromagnetic interference (artificial or otherwise) to prevent the Enterprise's sensors from scanning a planet or communicating with people on the surface.

My question is, how realistic is such a plot device, assuming either current-day or near-future sensory technology? If a planet had, say, a large-scale electrical storm or a lot of geothermal activity, would that be enough to obscure the surface of the planet from the sensors of an orbiting ship or a space telescope (aside from broad features such as continents and oceans)?

Thank you!