Legend of 1-15 days forecast (Ensembles of GFS) Ensemble consists 52 runs (or members) =1 operational run, 1 undisturbed control run but with a resolution of twice as much as operational run, 50 slightly disturbed runs based on operational run but also with a resolution of twice as much as the operational run.   Depicted are one control run and 10 slightly disturbed members. Upper values are forecasted temperatures at 850 hPa in °C (left column) Bold red line=30 years mean value Bold green line = operational run Bold blue line=control run Bold grey line=mean value of the 11 depicted lines Other colored thin lines=10 other (slightly disturbed) runs Bottom values are forecasted amounts of precipitation in mm (right column) Bold green line = operational run Bold blue line=control run Bold grey line=mean value of the 11 depicted lines Other colored thin lines=10 other (slightly disturbed) runs   T850 hPa is useful for forecasting Tmax temperature by adding a certain value (difference Tmax - T850 hPa) depending on season and amount of cloud.  Source experimental diagram: Alwin Haklander