The characteristics of global models are:
The forecast ist the result of a mathematical dynamical model: Atmosphere and the physical processes going on are formulated in form of the equations derived in physics. As neither these contained processes nor the actual measurements initialising the model can be complete, the forecasts are of course incomplete and erraneous. The longer the model is forecasting the less is the skill of the model. On the other hand are those models the only information about the processes taking place in the near future.