Deep Stable Layers in the Intermountain Western United States

Abstract

Abstract A deep stable layer (DSL) is a layer much deeper than a typical nocturnal inversion with stabilities not frequently found over a sizable portion of the lowest 1.5 km. They have traits that can cause the stagnation of cold air in basins, i.e., light winds at the surface even if moderately strong winds aloft are present, and the restriction of the growth of daytime convective boundary layers. The objective definition used in this study is that, if 65% of the lowest 1.5 km of the 1200 UTC [0500 mountain standard time (MST)] sounding has a lapse rate of 2.5°C km−1 or less, then the day is under the influence of a DSL. A climatology of days under the influence of a DSL was performed at four sites in the intermountain western United States: Grand Junction, Colorado; Salt Lake City, Utah; Winnemucca, Nevada; and Boise, Idaho. The DSL is a wintertime phenomenon with 10% to 20% of the days in December and January at the four stations being under the influence of a DSL. Successive days with a DSL present l...