So recently I've noticed people have been having problems understanding how to "see" instability/buoyancy on an observed sounding so I though I'd shed a little light on the subject. The amount of instability (CAPE) on a sounding can be eyeballed by looking at the parcel path relative to the temperature line. The parcel path of a sounding is the theoretical path any given parcel (imagine a box) of air would take in the environment. The temperature line is simply displaying the temperature on an X/Y axis throughout the atmosphere (millibars on the Y-axis and temperature values on the X-axis). Below is an example of a sounding with very high ML/SBCAPE values from June 29, 2012, a day that would produce a derecho that caused extensive damage from Ohio to Maryland:
The parcel path is represented with the dashed brown line and the temperature line is the red line. There is a large area in between the two indicating an extremely unstable environment and positively buoyant parcels (tendency to rise). The larger the area in between the parcel path and temperature line indicates high instability. Be wary though, there was also a thermal inversion at 850 mb which can put a damper on rising parcels due to the parcels not being warmer than the surrounding air at 850 mb (i.e. not having positive buoyancy).
While the thermodynamics for this sounding are very favorable for severe thunderstorms, the shear environment isn't favorable for
discrete severe thunderstorms i.e. supercells. This sounding however does show a favorable environment for linear thunderstorms, especially organized bows/derechos.
So when looking at soundings in the future, you can always eyeball it if the nice CAPE values below aren't available!
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