Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Johannesburg to Yellowknife as you normally would.
The rainfall in Johannesburg is generally less than the rainfall in Yellowknife. This will continue over the next 19 days.
With an average temperature of 26 °C, peak weather can be found in January. As a traveller, expect to see changes in flight prices during that period. The temperatures in Yellowknife are colder than in Johannesburg.