First, this one was written in 2014. The author looked at different U.S. cities and how often the barometric pressure in those cities changed by more than a certain amount. He then compiled a list of cities and ranked them from the cities where there is the least amount of barometric pressure variation, to those where there is the most.
The second article is from 2016. Now he has taken it a step further and looked at various countries around the world. He also put the data onto maps, by continent (scroll down to see the maps by continent).
Any idea what the ranges mean? You’re at like 0.02 and I’m at .2 which is half the highest at .37. But they’re averages, which smooth out quite a bit of variation. For example, you get hurricanes, we get drizzle. I don’t think barometric pressure is one of my triggers, so I have no idea.
If you scroll all the way to the bottom of the second link, you can download a large spreadsheet that contains all of the raw data. Here is the explanation for that data:
Saving the best for last, perhaps, feel free to download this Global-Barometric-Pressure-Threshold-Variation Excel spreadsheet. It contains the threshold variation percentage for every weather station with at least 50 daily change measurements since 2008, and the spreadsheet tabs provide both annual and month-by-month data. The spreadsheet is 3.5 MB is size, and so might take a little while to download on slower internet connections.
So, for example, if you live in Cape Town, South Africa, you could go to the Annual tab of the spreadsheet, use Control-F to search for “CAPE TOWN”, and see that at the Cape Town International Airport (CAPE TOWN INTL) has 14% of its days throughout the year (51 days) experience a barometric pressure variation of .20 or higher. If .20 pressure variation triggers a migraine headache every time, then a migraineur who lives in Cape Town could expect at least 51 migraines per year while living there. If you want to see whether this varies by season, which it does in every place that I’ve examined, you could go to the January tab, use Control-F to search for “CAPE TOWN”, and see that only 4% of days in January (perhaps one day each January) experience threshold variation. So the summer in Cape Town, as with most places, is a time of much lower barometric pressure variation. Looking at the winter in South Africa, in July, shows that 23% of days in July (an average of 7 days each July) experience threshold variation in Cape Town, which would be problematic for a migraine sufferer with a barometric pressure variation trigger.
This spreadsheet is the best way to see the month-by-month variation for the weather station closest to where you live.
@flutters, I looked at the raw data. I don’t see the units anywhere in his numbers, but I am pretty sure that the units are inches of mercury (Hg). He’s looking at the number of days per month where the barometric pressure changes by more than 0.20 inches of Hg during the day. His spreadsheet shows a percentage of days for a month, not the raw number of days.
(I used to have the MigraineX app installed on my phone. It’s supposed to display an alert when the barometric pressure in your area is forecast to rise or fall by more than a set amount, and I’m pretty sure that default amount was 0.20 inches of Hg.)
Anyway, I looked at the data for my area in Florida and it surprised me to see that the months with the highest number of days with more than a 0.20-inch variation in barometric pressure were in the months of November through February. I would have guessed that it would be during the summer. But the numbers were still very low:
January: 6% of days with a greater than 0.20-inch variation in barometric pressure February: 10% of days
March: 3% of days
April: 0% of days
May: 0% of days
June: 0% of days
July: 0% of days
August: 0% of days
September: 0% of days
October: 1% of days November: 4% of days December: 6% of days
For your area, I used the entries in the spreadsheet for “Seattle,” and it turns out the months with the highest number of days are October through March:
January: 34% of days February: 35% of days March: 42% of days
April: 29% of days
May: 21% of days
June: 11% of days
July: 2% of days
August: 4% of days
September: 14% of days October: 30% of days November: 39% of days December: 37% of days
January: 47% of days
February: 28% of days March: 48% of days April: 35% of days
May: 17% of days
June: 10% of days
July: 27% of days
August: 16% of days
September: 20% of days October: 38% of days November: 40% of days December: 43% of days
@Space_Cadet, I almost said “Do it yourself,” but since you asked so nicely…
January: 52% of days
February: 48% of days
March: 45% of days
April: 40% of days
May: 21% of days
June: 15% of days
July: 18% of days
August: 16% of days
September: 23% of days
October: 33% of days
November: 44% of days
December: 56% of days
Also, if you go back to the second post (the one titled “Global Variation…”), scroll all the way to the bottom and look at the comments left by people who read the post. Many of them point out that the methodology that the guy used for his statistical analysis missed places where there can be significant barometric pressure changes in just a couple of hours during a day. Several people used Florida as their example. In the summer in Florida, a thunderstorm can move in, dump a little rain, and move out in an hour or two.
@Manatee Thanks so much for posting these links! How interesting. I love the raw data, the time of year with the highest amount of barometric pressure change was not what I expected for Baltimore, but once I thought about it it made more sense.