Stability or instability prevailing in the atmosphere largely controls the daily weather. If there is stability in the atmosphere, it would resist vertical motions. Thus, stable air does not favour cloud formation.
However, when there are certain processes that force the stable air aloft, the clouds that form do not have great vertical thickness, rather they are fairly widespread.
Precipitation from such cloud types is invariably light. On the contrary, if the atmosphere is in the state of unstable equilibrium, the ascending air currents generally produce clouds with great vertical thickness.
There is greater convective activity and the resultant precipitation is in the form of heavy showers. Thus, the nature of precipitation itself is a sure indicator of the type of stability prevailing in the atmosphere.
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Light drizzle and overcast sky suggest the uplift or forced ascent of the stable air. By contrast, cumulonimbus clouds are suggestive of the ascent of unstable air.
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On hot summer afternoons, when the earth’s surface is intensely heated, the lapse rate becomes steeper leading to instability in the atmosphere. Surface irregularity often causes pockets of air to be heated more than the free air in the atmosphere.
The convectional currents are set up, and if they can reach above the condensation level, clouds form to yield occasional mid-afternoon showers. However, in such cases the clouds do not grow to great heights.
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The reason is that the “instability caused by surface heating does not extend to more than a few kilometers from the surface. Precipitation occurring in this way is generally of very short duration, because it cools the surface.
A temperature inversion produces the most stable conditions in the atmosphere. Because of the impact of an inversion layer in the atmosphere the air lying close to the earth’s surface is cooler and heavier than the air in the upper layers.
Therefore there is little vertical mixing between the layers of the atmosphere. This results in a greater concentration of pollutants in the lowermost layers. Similarly, an extensive fog is a sure indicator of atmospheric stability.
The development of clouds and the nature of precipitation occurring there from are all determined by the air stability or lack of it. Hence the state of equilibrium prevailing in the atmosphere determines to a large degree the type of weather we are going to have.