A record-setting heat dome is blanketing half the United States, exposing roughly 70 million people to triple-digit temperatures that officials warn could rapidly turn deadly.
The massive high-pressure system has settled over at least 15 states, including parts of California, Arizona, Nevada, Utah, Colorado, Oregon, Idaho, Montana, Wyoming, New Mexico, Texas, Minnesota, Nebraska and the Dakotas. Widespread extreme heat warnings have been issued in California, Arizona, Nevada, Utah and Colorado, and are expected to remain in effect through at least Sunday, with record heat lasting until late next week in some areas.
Las Vegas and Phoenix are expected to see temperatures surpass 115 degrees Fahrenheit throughout the weekend, and parts of Southern California could hit 120. The National Weather Service has warned that the risk of dehydration and heat stroke will be so severe that people should avoid drinking alcohol, eating high-protein meals or sitting in cars for any length of time.
"Car interiors will reach lethal temperatures in a matter of minutes," the agency said in a statement Friday.
Extreme heat above 120F can cause the body to struggle to cool itself through sweating alone, sending body temperature climbing and triggering heat stroke, a life-threatening emergency in which the body's systems begin to fail. This can happen even faster inside a car, which becomes a mini greenhouse with temperatures topping 150F within minutes, making hot cars especially dangerous for young children and pets.
The heat dome traps warm, humid air and prevents it from rising, sending temperatures across the region 10 to 20 degrees above normal averages for late July and early August. AccuWeather has predicted Las Vegas will see its daily temperature record shattered for five straight days starting Saturday, when the high is expected to reach 117F. Phoenix is expected to break its heat record on Friday, Saturday and Sunday, surpassing 115F each day.
Health risks mount
"Heat-related illnesses increase significantly during extreme heat events. Take extra precautions when outside. Wear lightweight and loose-fitting clothing," the National Weather Service said. "Try to limit strenuous activities to early morning or evening. Take action when you see symptoms of heat exhaustion and heat stroke."
Heat exhaustion often starts with heavy sweating, fatigue, cool, pale, clammy skin, a fast weak pulse, muscle cramps, dizziness, nausea and headaches. Heat stroke, which is far more deadly and can develop within 15 minutes in extreme conditions, often begins with a throbbing headache, confusion, slurred speech, nausea, dizziness and a fever above 103F. Sufferers may also develop red, dry or damp skin, a rapid pulse, and lose consciousness, and it turns fatal when the body's organs fail.
Anyone affected by these conditions should be moved to a cool, shaded spot right away, with emergency services called. The National Weather Service said elderly adults, children and people with chronic health issues or mental health conditions face the greatest risk, and urged them to stay indoors and use air conditioning.
Other major cities expected to feel the heat this weekend include Los Angeles, which could reach 100F, along with San Diego, Salt Lake City, Tucson and Palm Springs. AccuWeather warned that in areas where temperatures reach 115F and hotter, most outdoor activity should be considered dangerous, with cramps and dehydration setting in quickly without frequent rests in shade and water breaks.
Wildfire risk grows
The heat dome is also expected to combine with strengthening winds in the Northwest, sharply raising the risk of wildfires in several states.
AccuWeather meteorologist Chad Merrill said fire danger will spread east as dry conditions set off more fires and winds push smoke toward the Northern Plains, Midwest, Great Lakes and Northeast through August.
"Uncontrolled wildfires that are burning in an area where the jet stream winds are persistently strong will blow smoke downwind of the source region, usually to the east," Merrill said. "The smoke can be thick enough to obscure the sun during the day and lead to cooler high temperatures. In this case, the air quality suffers."
