The United States is experiencing its first significant heat wave of the 2025 summer, starting June 20, 2025, coinciding with the summer solstice. The National Weather Service (NWS) reports that the heat wave, driven by a heat dome—a high-pressure system trapping heat—began in the Great Plains and is spreading to the Midwest, Great Lakes, and East Coast, affecting over 255 million people. Temperatures are expected to soar 25–35°F above average, with heat indices (how hot it feels accounting for humidity) reaching triple digits, peaking at 100–105°F in many areas, including the Plains, Upper Midwest, and Mid-South. Cities like Denver may hit 100°F, potentially breaking daily records, while Philadelphia has issued a code red to protect vulnerable populations like the homeless.
The heat wave is particularly dangerous due to its early timing after a mild spring, leaving people unacclimated to extreme heat. The NWS warns that heat waves have doubled in frequency since the 1980s, with the season extending from 40 to 70 days, exacerbated by climate change. The summer of 2024 was the hottest on record, and 2025 is forecast to be similarly intense, with above-average temperatures expected coast-to-coast through August, especially in the West, Southwest, Florida, and New England. Vulnerable groups, including the elderly and children, face higher risks of heat-related illnesses like heat stroke, with symptoms including muscle cramps, heavy sweating, dizziness, and nausea.
The NWS recommends staying hydrated, wearing lightweight clothing, avoiding strenuous outdoor activities, and checking on vulnerable neighbors. The heat and humidity are expected to persist until late next week, with another wave possible in early July. Additionally, areas from New Mexico to New England may see heavy rain and flood risks due to moisture from a hurricane near Mexico. For detailed heat index forecasts, the NOAA’s HeatRisk tool provides color-coded risk maps.
