In 2011, Japanese researchers studied 28 migraine patients (full text here) living within 10 km of the Utsunomiya Meteorological Observatory in Japan to investigate whether atmospheric pressure may contribute to migraine symptoms. These researchers found that frequency of migraine  worsened when atmospheric pressure decreased by more than 5 hPa the day after the start of the headache. Conversely, migraine frequency improved when atmospheric pressure increased by more than 5 hPa within two days following the first headache.  In other words, symptoms worsened while air pressure was decreasing and improved with pressure increasing.

At page 1925 they wrote:

“In all the subjects, the headache frequency significantly decreased (p=0.02; odds ratio, 0.78) when the barometric pressure from the day the headache occurred (n) to 2 days after (n+2) was higher by more than 5 hPa (as compared with when the barometric pressure on (n+2) ranged from -5 to 5 hPa) (Fig. 3A). In the weather-sensitive group, the frequency of headaches significantly increased (p=0.009; odds ratio, 1.27) when the difference in barometric pressure from the day the headache occurred (n) to 1 day after (n+1) was lower by more than 5 hPa (as compared with when the difference in barometric pressure on (n+1) ranged from -5 to 5 hPa) and significantly decreased (p=0.02; odds ratio, 0.84) when the difference in barometric pressure from the day the headache occurred (n) to 2 days after (n+2) was higher by more than 5 hPa (as compared with when the difference in barometric pressure on (n+2) ranged from -5 to 5 hPa).”

In conclusion, they wrote at page 1926:

“We have shown for the first time that migraine headaches are associated with decreased barometric pressure on the following day, but are not associated with barometric pressure on the day the headache occurred. In our study, the frequency of headaches decreased when the difference in barometric pressure from the day the headache occurred to 2 days later was higher by more than 5 hPa, and increased when the difference in barometric pressure from the day the headache occurred to the following day was lower by more than 5 hPa. These results suggest that the headaches occurred during the fall in atmospheric pressure from the day of the headache to the following day.”

Of the 28 patients, 18 were thought to have symptoms correlating to changes in atmospheric pressure. That’s 64% of the patients in this study that were thought to be affected – a significant proportion.

The researchers do cover some limitations of this study at page 1927, including a relatively small sample size, that sample being overwhelmingly female and other limitations.  In this study they could not rule out the possibility of other contributing factors, such as temperature, humidity, sunlight etc.