Multiscale Analysis of a Meso-β Frontal Passage in the Complex Terrain of the Colorado Front Range

Abstract

Data from a mesoscale observing network are used to describe the evolution of a complex boundary between a dry air mass near the foothills of the Rocky Mountains and a shallow moist air mass over the eastern plains. Synoptic-scale analyses revealed that the origin of the moist air mass was associated with lee cyclogenesis. Mesoscale analyses provided a detailed picture of a localized anticyclonic circulation that developed within the larger-scale flow. Mixing ratio data from the mesoscale observing network indicated the position of the boundary between the air masses. It is shown that the cooler, moister air on the plains advanced toward and retreated away from the foothills during the evening. Eventually, downslope winds that were opposing the motion of the mesoscale boundary decreased, and the anticyclonic circulation on the plains became more organized. On an even smaller scale, Doppler lidar measurements revealed characteristics of the wind flow associated with the mesofront and the interaction of this flow with the downslope winds near the foothills of the Rocky Mountains. These characteristics included the horizontal variability of the winds near the complex foothills topography; the vertical structure of the winds associated with the mesofront, which indicated density-current-like features; the vertical structure of strong downslope flow opposing the mesofront?s motion; and differences in the aerosol content of the air masses.