Its true the comet has flared from mag 18 to mag 2.5 over the space of 24 hours! That would be a 1.5 million-fold flare in brightness, easily the largest recorded flare of comet. Its a pity its so low from here (and cloud and rain are forecast). At the moment the comet is being described as like a mag 2.5 nova in Perseus, it looks starlike lthough surely this will change as the dust cloud forming the coma expands..
Comet Holmes is a periodic comet and has been known to flare in the past. In fact it was discovered in 1892, possibly as the result of a major flare. See:
http://www.cometography.com/pcomets/017p.html
Terry