I have the same request. It would be great to be able to set the altitude to 100m (in my case), and have that remembered.
The forecast that appears when selecting a location is also locked to the surface altitude. If that forecast could display the currently selected altitude, that would be even better!
As it is, I have to select the 100m altitude, and select hour-by-hour on the timescale while watching the windspeed number on my selected point.
Cheers,
Jim