Today's forecasts for Whitehorse: on
yr.no, 17 with no rain until evening; from Environment Canada, 13 with showers from late morning. At 4pm it's currently 17.4 and no rain has fallen (and none looks like falling in the near future).
Not sure how the Canadians do their forecasting, but I'm guessing that they probably run a regional model covering southern Canada but it doesn't extend this far north, and for Yukon they're relying on global models?