I just read this webpage in detail for the first time, and the comment about atmospheric pressure changes intrigued me:
The cause of high altitude sickness is two fold, less oxygen and less pressure (they go hand and hand). At sea level, we have a reading of 29.92 inches of mercury, but this drops to 20.57 at 10,000 feet. This means that at 10,000 feet above sea level, you will have about 1/3 (31.25%) less pressure. Now if a low pressure weather system moves in, this can drive the above numbers down a bit lower. Meteorologists estimate that low or high pressure systems can make up to a 3 to 4 percent difference in the barometric pressure. Those who find themselves highly subject to altitude sickness may want to consider this when planning for a trip to higher altitudes.I suppose it's possible that the 3-4% difference in atmospheric pressure during a low pressure event could account for someone who summits Whitney just fine one time, but suffers AMS another trip - even though their acclimation regimen, diet, hydration, etc. may have been the same. I had never given much thought to the effect of weather on AMS, but I suppose it stands to reason that AMS might be more prevalent during a low pressure sytem than when a high is in place. That 3-4% may not sound like much, but for those prone to altitude issues, it may be worth bearing in mind.
