Abstract
This study describes a downslope wind storm event observed over the Medicine Bow range (Wyoming, USA) on 11 January 2013. The University of Wyoming King Air (UWKA) made four along-wind passes over a five-hour period over the mountain of interest. These passes were recognized as among the most turbulent ones encountered in many years by crew members. The MacCready turbulence meter aboard the UWKA measured moderate to severe turbulence conditions on each pass in the lee of the mountain range, with eddy dissipation rate values over 0.5 m2/3 s−1. Three rawinsondes were released from an upstream location at different times. This event is simulated using the non-hydrostatic Weather Research and Forecast (WRF) model at an inner- domain resolution of 1 km. The model produces a downslope wind storm, notwithstanding some discrepancies between model and rawinsonde data in terms of upstream atmospheric conditions. Airborne Wyoming Cloud Radar (WCR) vertical-plane Doppler velocity data from two beams, one pointing to the nadir and one pointing slant forward, are synthesized to obtain a two-dimensional velocity field in the vertical plane below flight level. This synthesis reveals the fine-scale details of an orographic wave breaking event, including strong, persistent downslope acceleration, a strong leeside updraft (up to 10 m·s−1) flanked by counter-rotating vortices, and deep turbulence, extending well above flight level. The analysis of WCR-derived cross-mountain flow in 19 winter storms over the same mountain reveals that cross-mountain flow acceleration and downslope wind formation are difficult to predict from upstream wind and stability profiles.
Highlights
Downslope wind storms sometimes occur on the lee of mountain ranges such as the RockyMountain Front Range (e.g., [1,2,3,4])
A rich array of instruments was deployed in the 2006 Terrain-induced Rotor Experiment (T-REX) to study downslope wind storms and related phenomena in the Owens Valley, California, in the lee of the Sierra Nevada [8]
Data were collected in all four transects on the upstream and downstream sides of the Medicine Bow Mountains (MBM); for one of the passes the Wyoming Cloud Radar (WCR) failed in intense turbulence on the lee side
Summary
Downslope wind storms sometimes occur on the lee of mountain ranges such as the Rocky. Mountain Front Range (e.g., [1,2,3,4]) Such terrain-induced non-linear flow phenomena can result in damaging surface winds as well as severe turbulence both near the ground and at higher levels, affecting flight safety (e.g., [5,6]). The present study documents a downslope wind storm, a deep updraft and rotors in the lee of the Medicine Bow Mountains (MBM) in southeast Wyoming, USA (Figure 1). This range is lower and narrower (in the cross-wind direction) than the Sierra Nevada or the Rocky Mountain Front.
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