In Part 1, the theory of Normal-Mode Rossby-Haurwitz waves (NMRHW) will be reviewed from Rossby (1939), Haurwitz (1937; 1940), to Kasahara (1980; 1981)  to provide predictions of their horizontal and vertical structures and their expected periods.  Part 2 presents results of a search for these predicted characteristics in three years of vorticity fields computed from European Centre Interim Analyses.  Results suggest that the largest scale (zonal wave number + meridional index <6) NMRHW can be identified.