I love, love the intensity of this entire image, especially how Snape's presence just holds Harry there. Harry, not daring to do anything unless Snape commands it. And oh, Snape is so not finished yet with what he's planning to do, and that's what seals it for me -- the promise of what is to come, with absolutely no need to rush (and no hope of a quick ending for Harry) when it's storming like crazy outside.
And the wine. Snape holding his glass so casually. He just exudes control. Ungh... *melts*