What are upper level low pressure systems and upper level high pressure systems?
Upper level low pressure systems are pools of cold, unstable air aloft with comparatively low air pressure readings. High altitude winds, including jet stream winds, blow around the perimeter of these systems and can encourage surface storm development. Sometimes upper level lows separate from the primary flow pattern, becoming “cut off”, with winds blowing all the way around such systems in a circular fashion.
References to upper level high pressure systems are less frequent, but upper highs are instrumental in creating blocking patterns that foster air pollution episodes and warm and dry surface weather beneath them.