Being near the mountains in Calgary Alberta, we get some extreme weather and barometric changes and I find my heads follow those. So I am going to vote pressure change. I have found going from hot to cold and cold to hot environments can trigger or increase a head as well. Like AC to outside or winter coming inside or going from warm inside to 30 below outside in the winter.
I did find, when I vacationed in the Bahamas, that my heads kinda leveled out and dropped some in intensity as the weather is pretty consistent along with sea level pressure. Now, I just need my healthcare to prescribe and pay for the bahamas....