Instability

The next severe weather term I’d like to cover is instability. Instability can be thought of as the amount of potential energy in the atmosphere. High instability values can be a good indication of severe weather.

Instability can be measured in two separate ways. The first of which is by looking at CAPE values. CAPE values are useful for telling you the amount of energy that is in the atmosphere. Generally, 1,500-2,500 J/kg CAPE values are enough to warrant concern in the spring. However, in the winter months, values of 250 J/kg warrant some concern, especially when coupled with high wind shear.

Instability can also be measured by looking at the Lifted Index. Values less than -4 generally are considered significant. However, in the winter months, a lifted index of -2 is enough to raise some concern. The lifted index is a measure of how much lift is in the atmosphere.

So, why is instability important? High instability values indicate a thunderstorm will build higher into the atmosphere. To build higher into the atmosphere, the storm must have a strong updraft. To have a strong updraft, a parcel of air must be able to accelerate quickly upward. This is directly attributed to instability. The stronger the updraft of a thunderstorm is, the healthier the storm is. This can help forecast severe weather such as hail, damaging winds, and tornadoes.

To find out more about instability, be sure to check out this great website by Meteorologist Jeff Haby.