POTENTIAL INSTABILITY- Also known as convective instability. Instability caused by dry air advecting over warm and humid PBL air.
With the cap in place, air below it can continue to warm and/or moisten, thus increasing the amount of potential instability. Or, air above it can cool, which also increases potential instability.
This in turn increases the amount of potential instability. Also, the air above it can cool, which also increases potential instability.
convective instability"1. An instability due to the buoyancy force of heavy fluid over light fluid overcoming the stabilizing influence of viscous forces. 2. Same as potential instability. 3. Same as thermal instability.
Potential instability at medium levels (circa 500 hPa/5 to 6km) is also required, as is an initial inhibiting factor (warm/dry air capping surface based instability) to allow the 'loaded gun' effect to build up.
 See also: Energy, Forecast, Surface, Instability, Clouds
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