Model: GFS (Global Forecast System) Global Model from the "National Centers for Environmental Prediction" (NCEP) Update: 4 times per day, from 3:30, 09:30, 15:30 und 21:30 GMT Greenwich Mean Time: 12:00 GMT = 13:00 BST Parameter: Relative Humidity at 700 hPa Description: This chart shows the relative humidity at 700 hPa. In the forefield of a trough line as well as at and near fronts (Jets), warmer less dense air is forced to ascend. As the ascending air cooles, the relative humidity increases, eventually resulting in condensation and the formation of clouds.This process is known as frontal lifting. High relative humidity at 700 hPa - equivalent to ca. 10,000 ft a.s.l. - indicates the areas of frontal lifting and thus the active zones of the current weather.