Why does cloudy weather sometimes cause headaches?

Probably a change in atmospheric pressure.

Some people sensitive to the change in atmospheric pressure. What you are experiencing is a barometric pressure headache. (Most likely it’s irritating your sinuses, so you are right about that.) The changes in pressure lead to changes in the oxygen level, which you might be sensitive to, as this can cause the blood vessels in your head to expand and contract to accommodate the lower oxygen levels.

Barometric pressure changes cause the headache. During hurricanes when extreme drops in barrometric pressure is observed it contributes to pregnant women going into labor.

Also, what can be a coincidence is during springtime when storms are plentiful in the upper ⅔’s of the US it is also a time when things are blooming, and allergies can contribute to headaches.

It may also have something to do with the quantity and quality of ions in the air. Prior to a storm, large numbers of positive ions build up on the ground, which is known to cause anxiety in people (and animals). After discharge by a storm, these are replaced with negative ions, which have been proven to have a soothing and anti-depressive effect.

@SmashTheState that is 100% true, I had forgotten all about that :)

For me, on a cloudy day I’m in a bad mood. When I’m in a bad mood, somehow I get a headache. Maybe it’s because of the stress that kind of gets created by people not liking to be around me. Then the headache puts me in a worse mood….a spiral downwards. By the next day it’s usually hunky dory.

If the cloudiness is accompanied by high levels of humidity that could also be a factor.

Allergies contribute to sinus congestion. If you are allergic to molds, there is an increase of mold growth with higher humidity levels thus congesting the sinuses increasing pressure and leading to sinus headaches.

CHEMTRAILS (artificial clouds made up of harmful chemicals) may cause headaches.