From AMS Glossary
(Or Siberian anticyclone.) An area of high pressure that forms over Siberia in winter and that is particularly apparent on mean charts of sea level pressure.
Its center is near Lake Baikal, where the average sea level pressure exceeds 1030 mb from late November to early March. This anticyclone is enhanced by the surrounding mountains that prevent the cold air from flowing away readily. In the center of the anticyclone the normal clockwise circulation is replaced by katabatic winds down the river valleys, but to the east along the Pacific Coast there is a belt of very strong northerly winds. The offshore flow is known as the winter monsoon. In summer the Siberian high is replaced by a low pressure area.