So the rain gauge conclusion is that it doesn’t matter if the rain is coming straight down or at an angle. Up to a point, the rain gauge will measure the correct amount of rain. If you go back to my earlier visualization, that we’re sampling a tube of air and raindrops above the top of the rain gauge, maybe instead of imagining tilting that tube and slicing it off diagonally, we should just imagine the drops coming down at an angle inside a tube that is vertical. Then, for every drop of rain that blows away and escapes the rain gauge, another drop of rain will be blown in and be captured by the rain gauge.
Of course, if there is a strong wind, and the rain is blowing sideways over the top of the rain gauge, you could get plenty wet, without any rain ending up in the gauge. Unlike a rain gauge, we collect rain from any direction.
Then again, I particularly enjoy the thought that a good wind vortex might actually pull some water from the gauge, resulting in negative rain!
