We examine the S-index data, obtained in the context of the Mount Wilson H\&K project for the nearby F-type star tau Boo, for the presence of possible cyclic variations on timescales below one year and ``phase jump{''} episodes in the observed S-index activity levels, to determine whether such features are persistent properties of the chromospheric activity of tau Boo and possibly other late-type stars. Within the Mount Wilson H\&K project tau Boo was observed during 1278 individual nights, albeit with a very inhomogeneous coverage ranging from 2 to 137 observations per year. Our analysis shows that periodical variations with timescales on the order of 110-120 days are a persistent feature of the Mount Wilson data set. Furthermore we provide further examples of ``phase jump{''} episodes, when the observed S-index activity drops from maximum to minimum levels on timescales of one to two weeks, hence such features also appear to occur on a more or less regular basis in tau Boo.