LOS ANGELES (REUTERS) - An extreme heatwave that has already shattered temperature records across the US South-west threatened on Friday (June 18) to push power systems to the brink of failure as residents cranked up air conditioners.
California power grid operators, who have so far been able to keep the lights on, issued their latest "flex alert" for Friday, asking homeowners across the state to conserve energy in the late afternoon and evening when demand surges.
The heat, which comes amid years of drought across the South-west, has strained power grids in California and Texas and fuelled the spread of wildfires.
"It feels somewhat apocalyptic with the record high heat, the smoke from wildfires tearing through the Sonoran desert and the news on the drought," said Ms Emily Kirkland, a communications organiser for a Phoenix non-profit group. "Just the 10-minute walk from my house to the light rail made me queasy."
The National Weather Service has issued excessive heat warnings for five states - California, Nevada, Utah, Arizona and parts of Colorado - warning that temperatures soaring well above 38 deg C can be dangerous.
"Very hot conditions will continue for interior areas through Saturday, followed by gradual cooling into next week. Until then, USE CAUTION as heat can be deadly! Most importantly, stay hydrated and never leave kids or pets in a hot car!!" the National Weather Service station for Los Angeles said on Twitter.
Temperature records have already been tied or broken in Salt Lake City, Palm Springs and elsewhere and record highs were forecast for Phoenix on Friday at 47 deg C.
"It's miserable, you literally just don't leave your house unless you have to," said Ms Hannah Knight, 20, a waitress at The Coronado coffee shop in Phoenix.
The diner has an outdoor dining area but "when it reaches over 110 (degrees Fahrenheit or 43 deg C), there's no way to make it comfortable," she said.
Many other cities were expected to come close to tying or breaking their daily records, including Las Vegas where a high temperature of 45 deg C was forecast.
A high-pressure ridge, or dome, over the South-west has been blamed for the heatwave.
"Every year it's hot in the South-west," National Weather Service meteorologist Bob Oravec said from the Weather Prediction Centre in College Park, Maryland. "It just seems to be more newsworthy when you have temperatures of 115 or so day after day. It's pretty hot."
Power systems in Texas and California have so far withstood the strain but operators said that if residents did not conserve energy in the late afternoon, rolling blackouts could be required to keep the system running.
In Texas, where temperatures have moderated, demand hit a record on Monday, according to the Electric Reliability Council of Texas (Ercot).
California's power demand peaked on Thursday at 41,364 megawatts and was expected to surpass that level on Friday, according to the California Independent System Operator, which operates the grid in most of the state. One megawatt can power about 200 homes on a hot day.
The heatwave extended to the Midwest, prompting weather services to issue advisories for Kansas, Missouri and Illinois, before a strong cold front brings relief by the end of the weekend. Temperatures in St. Louis and Kansas City, Missouri, were forecast to top 100 degrees (37 deg C) on Friday.
Relief, relatively speaking, is also forecast to come to the South-west at the beginning of next week, Mr Oravec said.