I was surprised to learn that the average in my town had only gone up 1 degree since the last update. I expected a bigger jump like yours, purely based on vibes.
For example, every +0C day in the winter leads to snow melt. The total amount of snow collected per winter depends highly on the number of +0C days in the winter. Your average temperature might only go from -11C to -10C, but if there are 20 additional +0C days, you might end up with a lot less snow cover.