CLEAR CREEK COUNTY, Colo. (CBS4) – It doesn’t happen very often, but Colorado had a rare mountain tornado touchdown near Mount Evans. Saturday afternoon at 2:51 pm. Thunderstorms strengthening over the mountains west of Denver were strong enough to produce a weak, short-lived twister. The National Weather Service has analyzed pictures from the area and confirms that it was a bona fide tornado.
Typically, these types of storms can produce what are known as cold air funnels. Which are not tornadoes but do develop from cold air pooling in the upper levels of a thunderstorm. And with differing temperatures at altitude wind shear can cause a funnel-shaped cloud to drop from a thunderstorm. These funnels tend to be very weak and almost never touch the ground.
CBS Denver has the full article