When a mountain station is at a level lower than the base of the clouds, the procedure for observing clouds is the same as at low-level stations. Mountainous country often provides clear vertical reference points, so information about cloud height or altitude can often be quite accurate. When clouds are observed below the station level, they should be indicated separately. A description should be given of the upper surface of these clouds, including features such as a flat or undulated surface, or the presence of towering cumuliform clouds above the top of the layer. When estimating the cloud amount, locations where mountains protrude through a patch, sheet or layer should also be considered as covered with clouds.