It's ash from the erupting Puyehue volcano, 60 miles to the West in Chile. Here's a shot of the streets of Bariloche last night....
..and here's more in English from Reuters.
UPDATE: Excellent photoshow of Bariloche and surroundings at La Nacion today, right here.
UPDATE 2: You want really really pretty photos of an erupting Volcano? Chile's La Tercera got really really pretty photos of an erupting volcano. h/t settydude