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I really love wearing an altimeter watch while in the mountains. I know that it's affected by weather, but unfortunately I don't actually know how it is affected. This usually causes me to ignore the altitude readings entirely when the weather is unstable (and thus altimeter readings are inconsistent), rather than use what I have with some kind of mental/watch correction.

So, what types of weather patterns impact the altimeter reading?

To still estimate the altitude, can I do a mental re-calibration and/or what features of the watch could I use to mitigate any changes due to weather patterns?

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  • Barometric changes and to a minor degree temperature affect it. Its tuned on a standard pressure&temperature so if real press&temp are higher, true altitude is higher than it shows and the other way around for lower press&temp. You normally calibrate it at known points, on topo map if you have it, on the closest weather stations data if available (and not too far as error increases with the distance from it), helicopter if thats where you are coming from etc, and go from there. Calibration against a gps can be unreliable at times... Do you really need readings that are spot on? – Erik vanDoren Jul 8 '16 at 12:53
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In simplest terms, as you climb, the air pressure around you decreases and your watch subsequently registers an increase in elevation.

However, thunderstorms are often associated with a low-pressure weather system moving in, which will also register on your barometer. This can erroneously be interpreted as an increase in elevation. Similarly, high pressure (clear weather) systems moving in can make your watch register a decrease in elevation.

Some modern watches have accelerometers in them that can sense when you are moving. Algorithms then determine whether a change in pressure is likely due to your climbing (moving, and in an upward trending motion) or due to weather (no movement). These calculations can increase accuracy significantly, but you'll still need to calibrate on a regular basis.

Some GPS watches like Garmin's Fenix 3 (which has an acceleromter) also can auto-calibrate elevation based on GPS information -- though GPS elevation is notoriously bad.

More accurately, the Fenix 3 can also use your smartphone connection to look up your elevation based on USGS survey data of your current location (given by the GPS). This is not automated, but can allow you to more precisely calibrate the watch as often as you feel necessary.

Without super-sensitive tech to register these pressure changes, you'll be hard-pressed to track this on your own in any meaningful way.

Finally, temperature does have some (albeit slight) effect on mercury-based barometers as the the density of the liquid changes causing variation in the readings (low pressure = more volume). Modern non-mercury barometers are not influenced by this to any significant amount.

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    Temperature has an effect on altimeter as barometric pressure does change with temperature. If you were to fly here in Canada you would be required to compensate for cold weather during approach, there are "altitude correction charts" but you could do -4ft every 1000s ft above reference station and every degree below standard temperature. In some conditions difference can be more than 700ft, an hiker doesnt have the problem of hitting something but OP wanted to know how to calibrate an altimeter and temperature has its effect on it – Erik vanDoren Jul 8 '16 at 17:57
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    @ErikvanDoren "here in Canada", we are (officially, at least) using metric system, though. – njzk2 Jul 8 '16 at 19:15
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    @njzk2, but when you are flying you work in feet, if just for curiosity you check an altitude correction chart example, you will find temperature indicated in Celsius and altitude in feet. Russia (and China) would instead use the metric system for altitude and distance. (Obviously an hiker is not a pilot and just reason in whatever system is comfortable with, its just a practical example of temperature affecting altimeters) – Erik vanDoren Jul 8 '16 at 19:50
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In a nutshell:

  • when the weather goes bad, pressure drops, your perceived altitude increases
  • when the weather clears, pressure rises, your perceived altitude decreases

Using a precise topographic map of your hike, re-calibrate your altitude watch whenever possible.

(At the start, at a summit, at a crossing,...)

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