Final answer:
High pressure systems aloft with low pressure at the surface typically indicate unstable and potentially severe weather, which may include storms, strong winds, or heavy rainfall. Meteorologists track these pressure variations using weather maps, monitoring isobars for changes that forecast weather events.
Step-by-step explanation:
High pressure systems aloft combined with low pressure at the surface can be indicative of severe weather conditions. When the atmospheric pressure is low at the surface, this usually means that moist air is rising and condensing, leading to cloud formation and potentially to precipitation. The movement of moisture and air within these pressure systems is what drives various weather events. For instance, storms or even hurricanes can be associated with such conditions when the pressure difference is substantial, causing strong winds.
Meteorologists use weather maps to track these pressure changes. Regions of high and low pressure are marked with "H" and "L" on these maps, and the areas of constant pressure are plotted as isobars. Changes in these pressure patterns can signal incoming weather changes, including the development of storm systems with potentially high winds and heavy rainfall. Overall, the combination of high pressure aloft and low pressure at the surface warns of an unstable atmosphere and the likelihood of adverse weather.