The federal weather agency says a stretch of high temperatures this week poses a risk to public health in areas of B.C.’s Southern Interior. Environment Canada issued a yellow-coded heat warning for the Okanagan Valley, Lillooet, South Thompson and Shuswap areas Wednesday. A notice says daytime highs will be in the mid-to-high 30s and overnight lows in the high teens Wednesday and Thursday. Humidex values may reach the high 30s on Thursday in the Okanagan and Shuswap. The agency advises watching for signs of heat illness such as fatigue, thirst and headache, and to move to a cool environment and drink plenty of water. An air quality warning is also in effect for the Fraser Canyon and South Thompson due to the Brunswick Complex fires burning near Boston Bar. Officials say rising temperatures and gusty winds over the next two days, as well as a risk of dry lightning, could escalate wildfire activity on existing fires and spark new blazes. British Columbians are urged to be fire smart heading into the weekend.