The U.S. National Weather Service is warning that a “widespread and significant” heat wave is expected to affect parts of the western United States over the weekend, including drought-hit areas. In its outlook issued Friday, the agency says a developing heat dome will spread from northwestern states into the northern Plains. Forecasters warn that oppressive daytime temperatures combined with potentially record-warm overnight lows will increase heat stress. The heat risk is described as “major to locally extreme,” with “Extreme” being the highest category on the NWS HeatRisk scale. One area of concern highlighted is the possibility of temperatures reaching about 110°F (43°C) on Sunday in parts of the northern Plains region. The NWS also notes that all-time temperature records are at risk of being broken, reflecting the magnitude of the expected heat. Across the affected regions, the forecast emphasizes that conditions could affect anyone who lacks adequate cooling or protection from extreme heat, not only people who are typically considered high risk.