Yes, they got a heavy snowstorm. Articulated buses have difficulty keeping control in heavy snow, the rear end swings too much and drags the bus with it. That isn't a problem with conventional buses as they're one piece, not two. If snow isn't removed from the roads soon enough, there isn't much of a problem. Ottawa gets more snow than Edmonton or Winnipeg (In fact, more than both combined. About 50cm more than Thunder Bay, even) so that is a problem there. That isn't an annual event, but it can happen. As for double decker buses, Ottawa is currently testing them (I assume due to the Articulated bus fiasco) so they would be a viable option, and probably cheaper?
Sydney Australia has two level trains lines for suburban routes, and GO is also bi-level. (For anyone who doesn't know.
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And at least you aren't a hilly city. An articulated bus going down Red River Road in a snow storm would probably end up embedded in PACI.