All this talk about Rossby waves, and the movement of waves west or
east dependent on wavelength.
Anyone would think the real world is simple.
However, can I put it to you that the flow you are observing at any
instant in mid-latitudes is due to Baroclinic waves, which are
modified by the Rossby Effect (the variation of Coriolis parameter
with latitude). It really is impossible to observe pure Rossby waves
at any given instant.

Len Wood
Wembury, SW Devon