So, Spring arrived yesterday, at least temporarily. The warm front I wrote about a couple of days ago passed through Ottawa around 9am Wednesday morning, as can be seen from this graph:

The blue line represents the wind direction. Leading up to 9am on March 7th, it was coming from between NE (45°) and E (90°). Between 9am and 10am, you can see the direction changed to come from roughly SSE (160°), which is basically when the front passed through.