I remember that there was once the variable "equivalent potential temperature" - a very important one for meteorologists!
It is a common variable found in the models as "theta_e" - since I am now Premium Subscriber, I would really love to see it back in the list!
Short explanation (source wikipedia):
" θ e {\displaystyle \theta _{e}} \theta _{e} is the temperature a parcel of air would reach if all the water vapor in the parcel were to condense, releasing its latent heat, and the parcel was brought adiabatically to a standard reference pressure, usually 1000 hPa (1000 mbar) which is roughly equal to atmospheric pressure at sea level. "
Which makes it such a nice variable to look at, because fronts are easy to detect in 850hPa and the amount of water can be derived with it as well.