A heat dome, where atmospheric conditions trap heat, was forecast to create sustained high temperatures and accumulating discomfort. Advertisement AdvertisementThe region's heat was forecast to continue through the week, with temperatures topping 100 F (37 C) even in normally moderate areas of Montana and Wyoming. Advertisement AdvertisementIt's not just the United States: A June heat wave devastated Europe, with France recording at least 5,700 more deaths than usual. In an already hot year, heat extremes are dangerousAuthorities warned that this heat dome will be dangerous. Children and older adults, along with people with medical conditions, are especially at risk of serious conditions including heat stroke.