Just finished a mountain flying and a back country flying course in CO. I am surprised how much the pressure changed between reporting stations that aren't very far apart, often between 15 and 50 miles. The weather is clear, no fronts, stable air - light winds for a couple of days, no frontal activity on the weather charts. Yet, here are the altimeter readings of a few nearby stations and airports: 30.16, 30.55, 30.61, 30.65, 30.75. Anyone know why the pressure differs so much between reporting stations in the Rocky's? My instructor wasn't sure. He thought it might have to do with the Continential Divide.