Castlegar NewsExtremely hot weather expected for next three days in regionHeat warning takes effectPhoto: Wikimedia, Creative Commons Heavy radiation of sun on the earth causing heat weave. A yellow level heat warning has been issued for the Kootenay - Boundary for today, according to Environment Canada (EC). The national weather service issued the warning late Monday, noting that the humidex values will reach 33 for today. “This is a heat warning. High temperatures may persist until Thursday, followed by a cooling trend.