How can the Earth be warming if Houston gets snow?

My latest letter to the Chronicle.

I'm certain there will be a letter flurry precipitated by the snow flurries, of global warming deniers saying "Aha! Snow in Houston.Global warming is a hoax!"
Well it isn't so simple. The truth is that global warming actually makes snow in Houston more likely. How can that be? Normally in winter the Arctic ices up and Canada becomes extremely cold. Occasionally Canadian air will head south and strike us, but not so often. The situation is fairly stable. But if you melt all the Arctic ice in the summer due to global warming, the sea gets warmer, and retains a lot more heat. That heat causes a high pressure area to form offshore, which tends to push the cold Canadian air south, so we are actually more likely to get snow and freezing spells in winter due to global warming.