@stephen-p
You require the forecast of this parameter. I am not sure that everyone here know what it is used for.
Delta T is the measure of evaporation rate and lifetime of a droplet. It is calculated by the dry bulb temperature minus the wet bulb temperature. This is important when spraying.
Wind displays the forecast temperature that is the dry bulb temperature in Temperature layer and in meteograms.
The Wet bulb temperature layer provides the forecast of this parameter.
So you need to calculate the difference between them. I doubt Windy provides directly the Delta T unless many users ask for it.
I guess this is for aerial spraying, not for ground spraying ?