Outdoor VMD definitely has some limitations with regard to filtering false alarms. Environmental effects are pretty hard to filter, but there are some best practices to try to avoid it.
In general the best way to set up motion detection windows is to set up long narrow windows sort of like trip-wires, and set the target size to a reasonably high value for what you are trying to catch. The higher the target size, the better it should filter other effects.
See this thread for a detailed step by step showing best practices!