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It is important to assess the potential influence of any inadequately resolved features and the subsequent downstream evolution and consequences.  A judgement of the medium-range performance should be based upon large upstream areas and also involve the upper-air flow.  A good or poor short-range forecast in an area does not mean the medium-range forecast there is necessarily similar.

Fig4.3-1:  Schematic illustration of the typical propagation of forecast errors over the northern hemisphere towards Europe in situations with generally zonal flow.  The errors propagate mainly along the storm track, which during the warm season, on average, is displaced polewards. Note however that in individual cases the propagation speed can vary greatly from what is shown here.

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