In the southern part of the state the bulk of rainfall comes from west to east moving cold frontal low pressure depressions, originating off the edge of the winter pack-ice in the Southern Ocean, south of South Africa. Cold southern airflows, wedging beneath humid north westerly winds triggers vertical instabilities, bringing this region the bulk of its rain between May and August. During the summer months these frontal depressions travel well to the south, leading to warm high pressure systems dominating the southern part of the state.