A record-breaking heatwave affects large parts of the United States ahead of the Fourth of July, with dangerous temperatures and high humidity. One report says that more than 130 million Americans across southern and Great Plains states are under a moderate to severe heat risk over the weekend. Authorities and forecasters warn that the combination of heat and humidity increases the danger of heat-related illness, particularly for people spending time outdoors or those without adequate cooling and hydration. The situation is described as widespread, spanning multiple regions rather than isolated local conditions. While specific temperature readings are not detailed in the provided excerpts, the coverage consistently frames the event as unusually intense and potentially harmful. The reports emphasize the need for heat-safety measures as the holiday approaches, including monitoring vulnerable individuals and following public health guidance. Overall, the sources agree that millions of people across affected states face elevated heat conditions during this period.