lies in the path of monsoon moisture from the Gulf of California. Most of the lowland areas receive less than of precipitation annually, although the I-15 corridor, including the densely populated Wasatch Front, receives approximately . The Great Salt Lake Desert is the driest area of the state, with less than . Snowfall is common in all but the far southern valleys. Although St. George receives only about per year, Salt Lake City sees about , enhanced by the lake-effect snow from the Great Salt Lake, which increases snowfall totals to the south, southeast, and east of the lake. Some areas of the Wasatch Range in the path of the lake-effect receive up to per year. This micro climate of enhanced snowfall from the Great Salt Lake spans the entire proximity of the lake. The cottonwood canyons adjacent to Salt Lake City are located in the right position to receive more precipitation from the lake. The consistently deep powder snow led Utah's ski industry to adopt the slogan "the Greatest Snow on Earth" in the 1980s. In the winter, temperature inversions are a common phenomenon across Utah's low basins and valleys, leading to thick haze and fog that can last for weeks at a time, especially in the Uintah Basin. Although at other times of year its air quality is good, winter inversions give Salt Lake City some of the worst wintertime pollution in the country. Previous studies have indicated a widespread decline in snowpack over Utah accompanied by a decline in the snow–precipitation ratio while anecdotal evidence claims have been put forward that measured changes in Utah's snowpack are spurious and do not reflect actual change. A 2012 study found that the proportion of winter (January–March) precipitation falling as snow has decreased by nine percent during the last half century, a combined result from a significant increase in rainfall and a minor decrease in snowfall. Meanwhile, observed snow depth across Utah has decreased and is accompanied by consistent decreases in snow cover and surface albedo. Weather systems with the potential to produce precipitation in Utah have decreased in number with those producing snowfall decreasing at a considerably greater rate. Utah's temperatures are extreme, with cold temperatures in winter due to its elevation, and very hot summers statewide (with the exception of mountain areas and high mountain valleys). Utah is usually protected from major blasts of cold air by mountains