Just before noon today I noticed that the sky to the north of the Ottawa River was nice and clear, while the sky to the south was overcast. Well, that’s because the boundary between the high pressure to the north and the low pressure to the south was more or less right there.
The temperature at Ottawa Airport a few minutes later (i.e. noon) was -5C, while in Pembroke about 2 hours to the northwest it was -12C and -16C in North Bay, which is a couple of hours past Pembroke.
If you check out the following two graphs, you can see the incoming cold air coming in from the northwest: