Snowing on just one place?

Two days ago I left home to take some pictures in the harbour. On the way I saw something strange in the woods nearby our home. It was very cold, -20 degrees Celsius and the sun was low in the sky. So it was a clear day, no clouds and sunshine. This is what I saw: it was snowing on a very small area and on a straight line. It was an area of only a few meters broad and about 40 meters long. I have never seen this before and can't explain how this is possible. Snow on a clear day I have seen before. This is what they call in Finland "pakkaslunta" which means that the humidity in the air is changing
to snow or ice during very cold temperatures. So if somebody understands what I saw that day, please let us all know.