If all you want is relative difference in altitude between your location and some other location, say a low-altitude weather balloon, you can use a MPL115A2 on the balloon and one at your location and the difference in atmospheric pressures will tell you the difference in height. Using the differential pressure method reduces the effects changes in the weather, note I said reduces the effects not eliminates. After working on systems like this I can tell you the baro method of height estimation will be more accurate then the GPS method in the majority of cases.