See the question and my original answer on StackOverflow

Sure. There is an example here: Example COM Class (C# Programming Guide).

The first thing you should do is locate the real (idl or c/c++) definition of the interface. For this SDK it's located for example in the <setup path>\Lockheed Martin\Prepar3D v4 SDK\inc\PDK\IWeatherSystem.h header file. This is where you will get the methods and the interface id (a.k.a. 'IID').

So in your case, it would be something like:

[Guid("e4452b96-16ba-4e82-9342-aa37af1f5c26")] // IID
public interface IWeatherStationV430 // IUnknown base interface is implicit
    bool IsValid();
    float GetSurfaceWind();
    void SetSurfaceWind(float aVal);
    // etc...