Numerical Simulation of the Life Cycle of a Persistent Wintertime Inversion over Salt Lake City

An episode of persistent wintertime inversion over Salt Lake City, Utah and its vicinity from 1200 UTC 30 November to 0000 UTC 7 December 2010 is simulated using an advanced research version of the Weather Research and Forecasting model. The numerical simulations agree well with observed soundings in temperature, wind speed, and wind direction in the atmospheric boundary layer and above, although there are some differences near the surface due to the influence of complex terrain in the area. The characteristics of large-scale environmental conditions and their interactions with local-scale processes are analyzed to understand the factors that influence the onset and evolution of persistent inversions. It is found that the inversion formed mainly because of the interaction between the heating effect from a high-pressure ridge in the mid-troposphere and a near-surface cold pool due to the effects of radiation. During the following six to seven days, the high-pressure ridge was maintained and vertical motion very weak, allowing a persistent inversion to become established. Finally, the cold effect from a low-pressure trough in the mid-troposphere, combined with mixing due to vertical motion, led to extreme weakening of the persistent inversion.