Unfortunately there was no mention of this in yesterday’s dev stream.
It really is a big problem.
It seems like the surface type (forest in this case) simply subtracts a sink value from the vertical wind above, regardless whether that rising air is caused by heat (surface thermals) or wind (ridge lift), which makes no physical sense.
If Asobo cannot distinguish between the different forms of rising air, they should consider decreasing the sink values for forest type terrain.