What are Lapse Rates?
Lapse Rates is what tells the decrease of temperatures the higher you go in the sky. It is also a measure of instability. The more difference there is between levels, the more instability there is.
How can you tell if the atmosphere is unstable?
Values in images less than 5.5-6 degrees in the images are considered very stable, while values near 9.5 degrees is considered incredibly unstable.
Below is a Sample Image from March 18, 2011.
In this image, we definitely see good instability in the Plains into the Midwest.