The national weather agency says temperatures for those areas on Saturday are expected to reach 35 C, with overnight lows falling to only 18 C. It noted, though, that temperatures will begin to moderate.
A heat warning was also issued for the North Thompson, with the mercury expected to reach 29 C.
For the Boundary region, Environment Canada is forecasting a 30 per cent chance of showers and a thunderstorm on Saturday afternoon, but says skies should clear in the late evening.
For Sunday through Wednesday, the Boundary region forecast is sunny with highs of 32 to 35 C, with overnight lows of 15 to 16 C.
For the Central and North Okanagan and the Shuswap, Saturday’s forecasts are similar.
Environment Canada is forecasting a 30 per cent chance of showers, with a risk of a thunderstorm late in the afternoon, along with a high of 32 and a low of 17.
Notably, in South Okanagan, Saturday’s forecast is mainly sunny with some clouds, and a high of 34 C.
For Sunday to Wednesday, the projected forecast is sunny, with highs of 28 to 33 C, and overnight lows of 15 to 16 C.
A severe thunderstorm watch is also in place for the Kootenays.
For more Environment Canada weather forecasts, click here.