Seas of Clouds as a Weatherscape for Low-level Clouds and Fogs

Seas of clouds (SOCs) attract mountain trekkers/photographers and are an important resource for rural tourism. The recognition of SOCs as a weatherscape in relation to low-level cloud/fog formation is described. Much of the information on the Internet explains SOCs as a low-level cloud/fog formation without considering the geographical conditions of observers. SOCs spots do not always represent meteorologically favorable conditions but are artificially advertised, and cloud/fog types that are the targets of SOCs change depending on the observer's altitude. High visibility is an important condition for the observer, otherwise it can be difficult to evaluate whether the clouds/fogs are in contact with the ground. Fog is also a weather type in which visibility is less than 1 km, so care should be taken not to confuse fog with the concept of SOCs, which require observers to have high visibility. At the foot of Mt. Yatsugatake, the modification of SOCs from midnight radiation fog to early morning low-level stratus and the development of stratocumulus clouds after sunrise and their dissolving with the development of valley winds were observed with an interval camera. Namely, the behavior of SOCs in mountains reflects the process of dry and wet atmospheres mixing at the top of a boundary layer to form a weatherscape. A case study of sunshine hour differences between Ueda and Sugadaira AMeDAS demonstrates important impacts of low-level clouds on the local morning weather in the valley where people live.