Because it is weather sensitive, it makes me think of my arthritis. I suggest you get her in to see a doctor. Even if it is not arthritis, she needs to know what it is as the pain you describe is not normal. Please let us know what they say.
I agree with txsilver- I have osteoarthritis in my lumbar region and I have the same symptoms. Only a doctor could diagnose her, but the shooting pains could be compressed nerves and that could be cause by arthritis or even simple bulging disks. I would start with her PCP they can at least order x-rays and get the ball rolling.
Best of luck to you and your wife!