What makes High and Low pressure, and is one more common during particular seasons?
High pressure is created by sinking, downward-moving air, while low pressure is created by rising air. That can be the result of global weather patterns...or very localized ones. For example...sinking cold air can created local zones of high pressure, while heating of the ground can result in rising air...and local zones of low pressure. In the Pacific northwest, high pressure is most common during the summer to early autumn months, while low pressure is most common during the late autumn to winter months.