Extreme-Value Climatology of Maximum Soil Freezing Depths in Contiguous United States

Extreme-value statistics for the maximum depth of soil freezing are developed based on a physical soil freezing model and a semiphysical soil water budgeting scheme. The model uses only daily air temperature, snow depth, and precipitation data. These data are available from a relatively dense network of observing stations, permitting the development of a national climatology of extreme soil freezing levels. A set of adjustment factors is also presented that allows conversion between the mapped base-soil freezing depths and those associated with other soil conditions. Surface cover characteristics of bare soil with and without ambient snow cover and turf are analyzed. The deepest soil freezing levels within the United States are found across the Dakotas, where persistent subfreezing winter temperatures, and relatively little soil moisture and snow cover combine to maximize soil freezing. Ample winter snow cover mitigates soil freezing extremes in the Great Lakes, northern New England, and western mountains. Soil freezing is unlikely south of northern Florida and the immediate Gulf Coast, along the California coast, and in southern Arizona.