[makeitdouble]

I assume parent means a period of time where the ambient temperature is at or above the wet bulb temperature.

[jcranmer]

Ambient temperature is always at or above the wet-bulb temperature, by definition. A wet-bulb temperature measures the temperature that can be achieved after energy loss due to evaporation of water, so as long as evaporation is possible (humidity < 100%), it is lower than the actual temperature.

[makeitdouble]

Thanks for the correction, I need to revisit the subject in full I think.