3. Stability

Determining Stability » Potential Instability Effects on Weather

The idea of potential instability and stability appears to be very simple, and the criteria for them are certainly very easy to use. But the relation of these states to the resulting weather is very complex and difficult to predict. The classic example of the release of potential instability in severe convection is when an air mass characterized by a dry layer overlying a surface moist layer is lifted. This is similar to the example we just examined.

Skew-T showing shallow potentially-unstable layer with potentially-stable air both above and below

There are, however, many other layers with less-marked potential instability, and the assessment of the type of weather that lifting will produce remains a challenge. For example, the sounding above shows a shallow potentially-unstable layer with deep layers of potentially-stable air both above and below. When lifted to saturation, this layer may produce any of the following:

  • A solid stratiform deck of cloud
  • Scattered shallow cumulus clouds
  • Mixed cumulus and altostratus clouds
  • Deep cumulus penetrating into the higher, stable layers with or without precipitation