A mountain range can have both a mechanical influence or a thermal influence, or a combination of the two. Mechanically, a mountain can force the air to go up and over the range or it can block the air and make it move laterally around the obstacle. Air parcels that have been displaced vertically often undergo a wavy motion downwind of the mountain. Sophisticated computer models used for weather prediction make better forecasts when they include the energy transports due to mountain waves. Bannon and a graduate student have documented the strength of Pennsylvania's mountain waves using high resolution data of the state's topography that includes Tussey and Nittany Mountains.
Mountains also affect the path of low-pressure cells or storms.
Typically a storm system off the west coast of the U.S. is deflected to the north, bringing rain to Seattle but sparing San Diego. The storm tends to weaken over the Rockies, only to reform and intensify over Colorado and Kansas. He has also studied the distortion of a cold front as it encounters a long mountain range like the Appalachians. A front is slowed upstream of a mountain, weakens as it move over the crest only to reappear stronger and steeper downstream. Bannon has also investigated the role of mountains in the summer monsoon of South Asia.