An unusually intense heat dome is bringing dangerous temperatures to parts of the West on Sunday, where about 45 million people are under heat alerts. Public health threat: The NWS warns of "major" or "extreme" heat risks across much of the region, indicating a widespread threat to public health from heat exposure. "Major" heat risk is not only centered on the Southwest, but will also stretch from Denver to North Dakota. When extreme heat risk is present, it indicates the heat could be deadly, particularly to those without cooling access. Extreme heat risk also means that health systems are likely to see increased demand, including with visits to the emergency room for heat-related illness.