We had a nor-easter the other day which brought high winds, gusting to nearly 40 mph, and swirling wind. Interestingly the snow accumulated on the western side of the trees. I have never seen such a thing in my entire life. I asked around for an explanation and the best was that the trees acted like a leading edge of a plane's wing and created a "vacuum" effect on the opposite side of the wind. As a scientist and keen observer of nature, I have no idea why I was never aware of this, and why, the meteorologist said that no one has ever asked this question before.
The constant air flowing by the round tree profiles creates a low pressure zone which attracts the particles to the back side. Were it to continue, eventually it would form a teardrop shape.
