The latest firmware update of Fenix 2 include a barometric pressure trend line which not yet included in the user manual. Since the similar trend line is come with Suunto Ambit 2, below show the extract from the manual:
You may also visit to http://en.wikipedia.org/wiki/Weather_forecasting to know more regarding weather prediction with barometric pressure:
Use of a barometer
Measurements of barometric pressure and the pressure tendency (the change of pressure over time) have been used in forecasting since the late 19th century. The larger the change in pressure, especially if more than 3.5 hPa (2.6 mmHg), the larger the change in weather can be expected. If the pressure drop is rapid, a low pressure system is approaching, and there is a greater chance of rain. Rapid pressure rises are associated with improving weather conditions, such as clearing skies.
So i am expecting a warm weather tonight:(