The act of spitting the cum that your partner unexpectedly deposited in your mouth back in his mouth. Some people may like this, but, in general, it is thought to be an act used to get back at a guy for cumming in your mouth without warning.
He came in my mouth without any warning, so I snowblowed the punk to get him back.
The act of getting back at someone for cumming in their mouth and not telling them. (I.e) After cumming in someones mouth that person then with out telling you, spits the spermies back into your mouth.
Previously the act of snow blowing was to "kiss your partner after they've ejaculated in your mouth, without expelling the semen" But the modern day act of snow blowing is to transfer the semen into the month of your unsuspecting partner. See also snow balling
When engaging in oral sex, a unique way to dispose of a mouthful of semen, is to try snow blowing.