Mountainous regions occupy a significant fraction of the Earth's continents and are characterized by specific meteorological phenomena operating on a wide range of scales. Being a home to large human populations, the impact of mountains on weather and hydrology has significant practical consequences. Mountains modulate the climate and create micro-climates, induce different types of thermally and dynamically driven circulations, generate atmospheric waves of various scales (known as mountain waves), and affect the boundary layer characteristics and the dispersion of pollutants.

At the local scale, strong downslope winds linked with mountain waves (such as the Foehn and Bora) can cause severe damage. Mountain wave breaking in the high atmosphere is a source of Clear Air Turbulence, and lee wave rotors are a major near-surface aviation hazard. Mountains also act to block strongly stratified air layers, leading to the formation of valley cold air-pools (with implications for road safety, pollution, crop damage, etc.) and gap flows. Presently, neither the fine-scale structure of orographic precipitation nor the initiation of deep convection by mountainous terrain can be resolved adequately by regional-to global-scale models, requiring appropriate downscaling or parameterization. Additionally, the shortest mountain waves need to be parameterized in global weather and climate prediction models, because they exert a drag on the atmosphere. This drag not only decelerates the global atmospheric circulation, but also affects temperatures in the polar stratosphere, which control ozone depletion. It is likely that both mountain wave drag and orographic precipitation lead to non-trivial feedbacks in climate change scenarios.

Measurement campaigns such as MAP, T-REX, Materhorn, COLPEX, i-Box, provided a wealth of mountain meteorology field data, which is only starting to be explored. Recent advances in computing power allow numerical simulations of unprecedented resolution, e.g. LES modelling of rotors, mountain wave turbulence, and boundary layers in mountainous regions. This will lead to important advances in understanding these phenomena, as well as mixing and pollutant dispersion over complex terrain, or the onset and breakdown of valley cold air pools. On the other hand, recent analyses of global circulation biases point towards missing drag, especially in the southern hemisphere, which may be due to processes currently neglected in parameterizations. A better understanding of flow over orography is also crucial for a better management of wind power and a more effective use of data assimilation over complex terrain.

To address these problems, we welcome contributions focusing on theoretical aspects, numerical modelling, field measurements, laboratory experiments, and downscaling or parameterization, within the following broad areas:

1. Mountain windstorms, gap winds, Foehn and Bora
2. Katabatic winds, slope flows and other thermally driven circulations
3. Upstream flow blocking and cold-air pools
4. Mountain wave dynamics and orographic gravity wave drag
5. Lee wave rotors and mountain wakes and vortices
6. Orographic precipitation and mountain hydrology
7. Interaction of boundary layers with orography
8. Mixing, transport, pollutant dispersion and air quality
9. Renewable energy and wind power in complex terrain
10. Forecasting, predictability and data assimilation of mountain weather
11. Climate change in mountainous regions

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