Effects of terrain on the horizontal and vertical structures of fronts over the Intermountain region

This talk will describe some observed effects of terrain on frontal structures over the Intermountain region of the western United States. Results from two landfalling frontal systems will be presented: one that featured an occluded system, and another that featured a well-defined cold front. The following occurred during both events: the low-level portion of the front was terrain-stripped or destroyed by the Sierra Nevada, a new surface feature redeveloped downstream of the Sierra, and surface and upper-level frontal structures became uncoupled. The evolution of the attendant precipitation system will also be described for one event, which featured a dramatic transition from a katafront (most precipitation is prefrontal) to anafront (most precipitation is postfrontal) configuration over 12h. This was due in part to relative humidity contrasts across the Sierra Nevada.