Observations of strong mountain waves in the lee of the Medicine Bow Mountains of southeast Wyoming

Strong winds in the atmosphere may be disrupted by mountain ranges creating strong waves and turbulence that are hazardous to aviation and creating damaging surface winds. Flow in complex mountain terrain is not well understood and until the recent development of remote sensing instruments, observations near the surface have been difficult to obtain.

In January and February 2006, a field campaign, utilizing the University of Wyoming King Air (UWKA), was conducted over the Medicine Bow Mountains in southeast Wyoming to study the formation of orographic precipitation. The UWKA is instrumented for in situ observations, including state variables of temperature, humidity, and winds and has probes for cloud microphysics. It is also instrumented for remote sensing with the Wyoming Cloud Radar (WCR). One upward-pointing and two downward-pointing beams of the radar allow for vertical profiling of clouds and precipitation in the atmosphere as well as dual-Doppler synthesis of the two-dimensional wind below the aircraft. Repeated flight legs were flown along the wind over the highest point, Medicine Bow Peak. On two occasions (January 26 and February 5), strong waves and turbulence were observed by the radar. Winds in excess of 30 m s-1 were measured near the surface. On January 26, vertical wind speeds in excess of 12 m s-1 were observed by the UWKA at the flight level of 3000 m, about 1000 m above the surface.

In this study we will examine the meteorological conditions under which these intense waves formed. The synoptic and mesoscale analysis from operational data will be combined with local, in situ observations from the UWKA. During both of the case studies the flow at ridge level is about 15 m s-1. The low level down-slope winds are about twice this value. Profiles were taken upwind of the mountain by the UWKA. On January 26, the more intense of the two cases, the Froude number is about 0.8. On February 5, it is about 1.05. A companion paper will present a detailed multi-Doppler analysis from the WCR of the waves and the turbulence.