Cerveny comments on the precipitation Dante describes in Hell's Plain of Burning sands, pointing out that blood snows are not uncommon in medieval writing:
He goes on to mention other reported incidents in Europe and the United States, on up until the end of the 19th century. The cause of such strange snow? The uplift and transfer of reddish sand particles.
Remember, as related in "How Weather Works," particles like this serve as condensation nuclei in raindrops and snowflakes. If the particles are red, then the resulting snow may fall red as well -- perhaps hundreds of miles from the initial uplift.
Of course, as Cerveny points out, the condensation nuclei in Hell would be actual bits of blood and gore from the boiling, sanguine River Phlegyas.
But expect more information on that in our upcoming podcast episode "The Science of Hell."