Large sections of the southern United States faced dangerous heat on Thursday, with the National Weather Service’s Norman, Oklahoma, office maintaining a Heat Advisory from midday to 8 p.m. Central Time. Actual temperatures were in the upper 90s Fahrenheit and, when combined with high humidity, pushed heat-index readings to between 105°F and 110°F across Oklahoma and parts of North Texas. Farther west, California’s Office of Emergency Services urged residents to limit outdoor activity as triple-digit conditions persisted in several inland counties. The agency reiterated guidance for outdoor workers to take frequent breaks, stay hydrated and seek shade, underscoring the strain prolonged heat can place on power grids, public health systems and vulnerable populations. The extreme conditions extend south of the U.S. border. Mexico’s federal Health Ministry reported 49 heat-related deaths so far this season, led by the northern state of Sonora with 14 fatalities and Veracruz with eight. Health officials warned that sustained exposure to temperatures above 37 °C (98.6 °F) can quickly trigger heat stroke and other life-threatening illnesses.