A reader asked: “The forecast had mentioned that the surface pressure was decreasing. However, it also stated that stability was increasing. Does this not seem counterintuitive?”
In a general sense, yes. High pressure at the surface is often found where there is slow, steady, sinking air due to air converging at the top of the troposphere. In a sinking airmass stable layers become more stable. This is because as a layer sinks it compresses. In contrast, above a surface-low air is rising slowly and stable layers are becoming less stable.
However, it is not quite that simple. If it were only about surface pressure, we would not need to consider soundings, horizontal movement or advection of different air temperature and humidity at different levels, cloud cover, or even air pollution.…
