  Long-lasting, very bright multiwavelength flares of blazar jets are a curious
phenomenon. The interaction of a large gas cloud with the jet of a blazar may
serve as a reservoir of particles entrained by the jet. The size and density
structure of the cloud then determine the duration and strength of the particle
injection into the jet and the subsequent radiative outburst of the blazar. In
this presentation, a comprehensive parameter study is provided showing the rich
possibilities that this model offers. Additionally, we use this model to
explain the 4-months long, symmetrical flare of the flat spectrum radio quasar
CTA 102 in late 2016. During this flare, CTA 102 became one of the brightest
blazars in the sky despite its large redshift of $z=1.032$.
