You’ve always been taught to use a flash indoors, and don’t use it outdoors. Think just the opposite. Flash indoors is harsh and not as beautiful as natural lighting. In addition, it can ruin the color of certain scenes.
Use a flash outdoors to light a person who is standing in an overly back light environment. Otherwise they will be a silhouette. You may want a silhouette, but if you don’t, use a flash.
Use a flash to fill in your subjects’ faces when in harsh sunlight. Use your camera’s “fill flash" setting if it has one.
Don’t pack up your gear when the weather gets cloudy. Outdoor photography is great on cloudy days. Things can be beautiful even after a rain. If the day is too cloudy, go ahead and shoot anyway—it’s easy to add “pop” to your photos in Picasa or Photoshop.
People’s reaction to weather can add interest to a photo. Snow never stopped me from taking a picture.