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Patrick A. Reinecke and Dale R. Durran

propagation of uncertainties in the specification of initial conditions, the predictability of forecasts for mesoscale motions with spatial scales on the order of 10 km would be limited to time scales on the order of 1 h. This discouraging prospect has largely been supplanted by a more optimistic view based on experiences with high-resolution NWP models demonstrating that realistic mesoscale circulations can be generated during the forecast without having to specify mesoscale precursors to these

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Peter Sheridan and Simon Vosper

1. Introduction The Sierra Nevada range is a well-known source of strong mountain waves, downslope windstorms, and turbulence associated with lee-wave rotors, which represent hazards to aviation, residents, and property and are difficult for forecasters to predict ( Holmboe and Klieforth 1957 ; Grubisic and Lewis 2004 ). Continued increase in the resolution of operational numerical weather prediction (NWP) models is expected to improve forecasts as the phenomena become more explicitly resolved

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James D. Doyle, Qingfang Jiang, Ronald B. Smith, and Vanda Grubišić

, and (iii) evaluate the ability of high-resolution models to forecast the wave characteristics including three dimensionality. The paper that addresses these points is organized as follows. A description of the numerical model is contained in section 2 . The observational analysis is presented in section 3 . Numerical simulations results are discussed in section 4 and the summary and conclusions appear in section 5 . 2. Numerical model description The numerical simulations of

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Yanping Li, Ronald B. Smith, and Vanda Grubišić

Valley observations from the Terrain-Induced Rotor Experiment (T-REX) project. In section 4 we propose a novel approach for estimating the valley daily maximum mixed-layer depth using surface pressure and temperature amplitudes. Idealized 2D Weather Research and Forecasting Model (WRF) simulations are described in section 5 , together with a discussion of the physical processes involved in producing surface pressure and temperature variations in mountain valleys. Section 6 gives the results of

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Patrick A. Reinecke and Dale Durran

1. Introduction Accurately forecasting orographically generated internal gravity waves is a significant challenge for mesoscale numerical weather prediction (NWP) models. More commonly known as mountain waves, these features occur when stably stratified air is forced over a topographic barrier. While NWP models have steadily advanced over the last several decades, opportunities to verify model forecasts of mountain waves against observations are limited to a handful of field campaigns. Several

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Shiyuan Zhong, Ju Li, C. David Whiteman, Xindi Bian, and Wenqing Yao

Sierra Nevada. The combination of high winds and the dry, alkali soils of the Owens Lake bed produces some of the highest concentrations of particulate matter with diameter less than 10 μ m (PM 10 ) observed in the United States ( Reheis 1997 ). Forecasting these high wind events has proven to be challenging because forecast models often perform poorly in this region because of the prominent mountain barrier and the steepest orographic gradient in the contiguous United States. The lack of

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Georg J. Mayr and Laurence Armi

that foehn occurs when potential temperatures at the downstream valley floor become at least as high as the potential temperature on the upstream side at barrier height ( Mayr and Armi 2008 ). The strength of cross-barrier flow remained almost unchanged before and after in the Alpine cases and the event here and is thus only of secondary importance. A forecaster will need to predict the evolution of both upstream barrier height temperature and downstream valley temperature correctly in order to

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James D. Doyle, Saša Gaberšek, Qingfang Jiang, Ligia Bernardet, John M. Brown, Andreas Dörnbrack, Elmar Filaus, Vanda Grubišić, Daniel J. Kirshbaum, Oswald Knoth, Steven Koch, Juerg Schmidli, Ivana Stiperski, Simon Vosper, and Shiyuan Zhong

including sensitivity of mountain-wave predictions to the model formulation. During the Terrain-Induced Rotor Experiment (T-REX; Grubišić et al. 2008 ), high-resolution forecasts were routinely conducted to assist in mission planning using a number of different three-dimensional nonhydrostatic numerical models such as the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS 1 ; Hodur 1997 ), two dynamical cores of the Weather Research and Forecasting model (WRF), namely the Advanced Research

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Qingfang Jiang, Ming Liu, and James D. Doyle

optimum interpolation analysis of upper-air sounding, surface, commercial aircraft, and satellite data sources that are quality controlled and blended with the 12-h COAMPS forecast fields. Lateral boundary conditions for the outermost grid mesh are derived from Navy Operational Global Atmospheric Prediction System (NOGAPS) forecast fields. The 36-h forecast period runs from 0000 UTC 25 March to 1200 UTC 26 March with a data output frequency of 5 min. b. Aerosol model A dust microphysical aerosol model

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Juerg Schmidli, Brian Billings, Fotini K. Chow, Stephan F. J. de Wekker, James Doyle, Vanda Grubišić, Teddy Holt, Qiangfang Jiang, Katherine A. Lundquist, Peter Sheridan, Simon Vosper, C. David Whiteman, Andrzej A. Wyszogrodzki, and Günther Zängl

1. Introduction Over mountain areas the evolution of the boundary layer is particularly complex as a result of the interaction between boundary layer turbulence and thermally induced mesoscale wind systems, such as the slope and valley winds (e.g., Rotach et al. 2008 ). As the horizontal resolution of operational forecasts progresses to finer resolution, a larger spectrum of thermally induced wind systems can be explicitly resolved. It is therefore useful to document the current state

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