A massive heat dome parked over the southern United States has placed more than 50 million people in Arizona, Arkansas, California, Louisiana, New Mexico, Oklahoma and Texas under extreme heat warnings or heat advisories, the National Weather Service announced on Monday.
Texas is forecast to be hit hardest, with Dallas, Fort Worth, Houston, San Antonio, Austin, Lubbock, Odessa and El Paso all caught under the high-pressure system blanketing the Southwest.
Phoenix and Tucson in Arizona, San Diego and Los Angeles in California, Shreveport in Louisiana, and Oklahoma City have also been warned of a potentially deadly combination of extreme heat and high humidity lasting until at least 8pm local time. California's warnings remain in effect until Wednesday, while Arizona's are expected to last until Saturday night.
"An extreme heat warning means that a period of very hot temperatures, even by local standards, will occur," a National Weather Service spokesman said.
Temperatures in the Phoenix area are expected to reach between 106 and 118 degrees Fahrenheit in the afternoons this week. In Texas, forecasters are bracing for near-record temperatures that could reach 112F on Monday, affecting roughly 25 million people in that state alone.
Extreme heat risk levels
The National Weather Service classified conditions in Texas on Monday as "major" or "extreme" on its heat risk guidance chart, the two most serious levels on its five-stage alert system. Extreme conditions bring "no overnight relief" from the heat and threaten anyone without air conditioning or proper hydration, according to the agency.
Dallas, Fort Worth, Austin and Houston were all listed in the extreme heat zone on Monday. By Wednesday, the worst of the heat and humidity is projected to shift west toward Arizona and Southern California, affecting Phoenix, Tucson and Los Angeles.
Safety warnings from officials
"Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors," National Weather Service officials said. "Do not leave young children and pets in unattended vehicles. Car interiors will reach lethal temperatures in a matter of minutes," they added.
Record temperatures expected in Phoenix
Forecast highs of 114F on Tuesday and 116F on Wednesday in Phoenix are expected to break or challenge the city's single-day records, both of which were set in 2011.
Multiple heat domes have formed over the United States this year, starting unseasonably early in mid-March. Heat domes trap both hot air and high humidity close to the ground, acting like a lid over large portions of the country for days at a time.
Who is most at risk
Officials urged anyone who has to go outside to wear lightweight, loose-fitting clothing and to limit strenuous activity to early morning or evening hours. The elderly, pregnant women, newborns, young children and people with chronic health problems such as heart disease, obesity or poor blood circulation face the highest risk from heat-related illness.
Heat exhaustion, which occurs when the body overheats after prolonged exposure to hot weather, can cause heavy sweating, fatigue, cool, pale, clammy skin, a fast and weak pulse, muscle cramps, dizziness, nausea and headaches.
Heat stroke is far more deadly and can develop within 15 minutes in extremely hot conditions. It 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 loss of consciousness, and the condition turns fatal when the body's organs begin to fail.
Drought and wildfire concerns
The heat is expected to worsen an already severe drought across the Southwest, which may soon lead to water shortages in several states. The US Drought Monitor has found that conditions in northern Texas, western Oklahoma and parts of New Mexico have reached the monitor's most severe level, known as D4 or "exceptional drought."
Large portions of nearby Colorado, Idaho and Oregon have also moved into D4 status, raising the risk of dangerous wildfires across the western United States this summer.
