Profiling Radar Observations and Numerical Simulations of a Persistent Downslope Windstorm and Rotor on the Lee of the Medicine Bow Mountains, Wyoming

We analyze a downslope windstorm event that was observed over the Medicine Bow Mountains on 11 January 2013 during the AgI Seeding Cloud Impact Investigation (ASCII) field campaign. The University of Wyoming King Air (UWKA) made four along-wind passes during a five hour period over the target mountain. Several in-situ measurements as well as the Wyoming Cloud Radar (WCR) were onboard the UWKA to measure the upwind and downwind atmospheric conditions. In addition, three rawinsondes were released from an upstream location at different times within a period of nearly ten hours. All four WCR transects indicate a persistent downslope windstorm, wave breaking, hydraulic jump and rotor. The in situ measurements at flight level reveal very high turbulence in the leeside hydraulic jump, reaching the severe turbulence condition based on the measurement of eddy dissipation rate (maximum measured value is 0.51 m2/3 s-1) by the MacCready turbulence meter. The WCR measured Doppler vertical velocity shows a turbulent, deep hydraulic jump, up to ~5 km deep (7 km MSL), about 4 times deeper than the mountain is high. A dual Doppler synthesis of the two-dimensional velocity fields in the vertical plane below flight level reveals rapidly accelerating plunging flow in the lee of the crest, and a rotor with reverse flow further downwind. This case is also simulated using the non-hydrostatic Weather Research and Forecast (WRF) model at 1 km resolution, to analyze the dynamics of the event. A detailed dynamical analysis and comparison of observed downslope windstorm and rotor formation with the model simulation will be presented