The effect of decoupled low-level flow on winter orographic clouds and precipitation in the Yampa River Valley

Abstract

The first method involved analysis of one and a half months of precipitation and wind data from a 24-station mesonetwork located in the Yampa River valley and surrounding mountains of northwest Colorado during the winter of 1981/1982. The second method was a case study analysis of two orographic storms using data from an instrumented cloud physics aircraft to supplement the data from the mesonetwork. The third method involved two-dimensional numerical simulations. The results show that the presence of extensive low-level decoupled flow causes part of the orographic lift of the mountain barrier to be experienced upstream of the barrier. This changes the location of condensate production which in turn shifts precipitation upstream and appears to enhance the precipitation efficiency for the entire barrier. -from Authors