I've had chronic daily migraine for 44 years. I recently had a septoplasty (against the advice of 4 neurologists); even the ent said it wouldn't help the migraines, but I'd breathe easier.
My triggers have always been hormonal as well as weather related (I had a total hysterectomy solely because I thought it would help my headaches; it didn't). The turbinates in the nose swell in response to hormones and barometric pressure. I've been carrying nose drops in my purse since I was a kid, and every time I lie down my nose gets stuffy. Sure enough, it turns out my septum was so deviated to the right that it actually touched the opposite side of my right nostril, visibly pulling my left nostril towards the right, making it look narrower.
As it happens, the septoplasty is the only thing I've ever done over the course of 44 years which has had a significant positive impact on my migraines. I still get them, but they are not as severe. Over the last 5 weeks I've only been down for the count for 4 days, and it has rained a lot more than 4 days in that time. That is an incredible improvement!
This may not be the answer for every migraineur who also has a deviated septum, but it's definitely worth a try. It's an easy surgery, and even if it just helps you breathe easier, it's worth a try. I had doctors from one of the most prestigious headache clinics in the country advise me strongly against the septoplasty, saying that it couldn't help the headaches in any way. They were wrong. It's one more thing to look into.