Southern Appalachian Cold Air Damming (CAD): A Climatology and Simulation of Case Studies

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Sunday, 4 January 2015
Jared Rackley, Univ. of Georgia, Athens, GA; and J. A. Knox

Cold air damming (CAD) occurs when a shallow, surface-based layer of relatively cold air becomes entrenched against the windward side of a mountain chain. In the US, CAD forms along the eastern slopes of the southern Appalachians. CAD is known to have a significant effect on sensible surface weather conditions including temperature, precipitation type, and cloud cover. Though numerical weather prediction model forecast accuracy of damming events has improved drastically in the last several decades, CAD still often thwarts forecasters. A 30 year climatology (1981 2010) of CAD events in the southern Appalachians was conducted using hourly surface observations and North American Regional Reanalysis (NARR) data. Analysis of the frequency of CAD events and CAD event types on a month-by-month and year-by-year basis is generally consistent with previous CAD climatologies, though, results do show some variation due in part to this study's longer period. Results confirm that CAD is much more frequent during the cold season versus the warm season, with CAD occurring most often (by average number of events and hours per month) during the month of December. July recorded the lowest average number of CAD hours per month during the period, while June showed the lowest average number of events per month. Additionally, analysis of the spatial distribution and frequency of cold air domes sheds light on a previously unexplored aspect of southern Appalachian CAD events and their impact on the Southeast. This study denotes unique patterns in the spatial distribution of cold air domes for cold and warm seasons and differing CAD types. Specifically, different CAD types exhibit one of two spatial patterns in the southernmost extent of the cold air dome: a more southerly dome with a ridge axis oriented from north-northeast to south-southwest or a more westerly dome with a ridge axis in a more northeast to west-southwest orientation. CAD is shown to occasionally penetrate farther west than Birmingham, Alabama, and farther south than Tallahassee, Florida. The Weather Research and Forecasting model (WRF) is also used to investigate an unusual case study of CAD in the Southeast and explore the impacts of wedge fronts on convection.