If you're using a iPhone 6, 6 Plus or an iPad Air 2 you will be able to read directly the current pressure reaching the internal sensor.
The widget available in the notification center can give you the pressure or the current temperature depending on your settings.
Easy Weather give you the ability to use your phone as an awesome barometer.
The full app color will change with the pressure variation with a magic effect.
After a few days, you will be able to understand how the weather updates around you.
The barometer it the best way to anticipate the coming weather.
Do not wait anymore, and start making your own forecast.
With this app you will learn how to make your own forecast.