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: Geopotential height (solid line) Temperature (colored, dashed) at 500 hPa
Description: Geopotential height at 500 hPa (solid line)
Temperature at 500 hPa (colored, dashed)

The maps show the predominant tropospheric waves (trough or ridge). They virtually control the ''weather'' (dry, warm / wet, cold) and the long waves drive the smaller synoptic waves. Thus, this upper-level chart illustrates the dynamics of our atmosphere.