For me, when I am shooting landscape photography, what I look for more than anything else is transitional light. Taking pictures outdoors when the weather is changing provides more contrast as some parts of the land are hit by light, while others are not. And the clouds themselves can add great drama to the picture.
The natural tendency is to avoid stormy days when it might be raining, snowing or windy. Personally, though, I find these times to afford the opportunity to make some of the most dramatic images possible. It's important to be prudent, and stay out of dangerous situations created by severe weather. Shooting with lightning in the area, or chasing tornadoes are not things I would recommend, for example. With that in mind, the next time a weather system rolls through, think about getting out and making some images.