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How to predict the weather in the mountains with altimeter and barometer

The weather is always one of the great thoughts for those who go to the mountains, whether you want to take a simple trip or think of something more challenging. As long as you are at home or otherwise you can use your smartphone there are good apps for weather forecasts, but problems start when you are in areas where the phone does not take and you still have to somehow predict the time it will take.

It is possible in these cases to forecast the weather using an altimeter and a barometer, which are often found in watches or GPS navigators for outdoor and hiking, or knowing the atmospheric pressure (often in the shelters a barometer is there) and l 'altimetry of the point where you are located, which is marked on the maps or on the signals that are found in the mountains.

What to do to forecast the weather in the mountains with altimeter and barometer

To make weather forecasts with altimeter and barometer, firstly it is important to know precisely the altitude at which you are located and then do some simple mathematical calculation starting from the atmospheric pressure at sea level, which is 1013.25mb. On average, the atmospheric pressure drops by 1 millibar every 10 meters of altitude, so knowing the altitude at which it is located it is possible to calculate the average atmospheric pressure at that altitude.

For example, at 2500 meters above sea level the atmospheric pressure will be 1013.25mb - 250mb = 763 mb

Once you have calculated the average atmospheric pressure at the altitude you are in, you need to know the current atmospheric pressure at the moment, and this can be done with the barometer. From the fact that there is high pressure or low pressure you can then make a prediction about how the weather is evolving.

High pressure means good weather, low pressure bad weather

In general the high atmospheric pressure means presence of good weather while the low pressure means bad weather. So, in the example of 2500 meters altitude, if the pressure is higher than 763mb there is good weather, if it is lower there is bad weather. But this does nothing but photograph the current situation and is not very useful. Instead, it is more useful to predict the time that will be there in a few hours, and this can be achieved by making different measurements: if indeed there is good weather, then with atmospheric pressure higher than the average of the altitude you are in (in our example 763 mb), but the trend is decreasing up to 763 mb or even less it is foreseeable that the weather will worsen; vice versa in the case where the measured pressure has the tendency to grow and exceed the average of the quota to which it is found, even more so if these dynamics of rising or lowering of pressure are fast or sudden.

Predict the weather with Altimeter GPS

The Altimeter GPS app uses the integrated barometer of your iPhone (available from iPhone 6S or higher). It shows useful indications such as atmospheric pressure and weather forecast based on the barometer.

The data displayed are the result of the sensors in the mobile device, ie the GPS and the barometer. If the latter is not available in the terminal, the data will be less accurate as the app will be based on data from local weather stations, if available.

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