The Worse the Weather, The Better the Picture Opportunities
When photographing wildlife bad weather often means good pictures. When the weather is bad wildlife patterns are often disrupted creating opportunities. If the weather is cold or stormy wildlife will often spend more time feeding making them easier to locate and creating more photographic opportunities. Beyond that, bad weather creates more interesting environments for picture taking. Fog, mist and rain can soften backgrounds making it easier to isolate subjects. Wet surfaces create reflections while snow often adds interest and mood.
So, if the weather is bad, dress appropriately, and head out to get that unique picture.