A punishing heat dome will only worsen. Here’s when temperatures could peak

By Mary Gilbert, CNN Meteorologist

(CNN) — A brutal heat dome is ramping up and sending temperatures to dangerous levels in California and the West in what is the region’s first significant heat wave of the year.

And heat hasn’t peaked yet. July-like high temperatures will top out at 20 to 25 degrees above normal in multiple Western states this week and could break several daily record high temperatures. Thursday will be the hottest day of the week for millions of people.

The temperatures will be dangerous for those exposed to the elements and unable to cool off. Relief from the heat won’t be found at night, either – another symptom of a world warming due to fossil fuel pollution.

The extreme heat already turned deadly over the weekend with worse to come.

Excessive heat warnings are in effect for nearly 19 million people in California, Nevada, Arizona and Utah and South Texas. The warnings are the most extreme form of heat alert issued by the National Weather Service and are used when widespread, dangerous heat is expected.

The soaring temperatures are being caused by a heat dome, a large area of high pressure that parks over an area, traps air and heats it with abundant sunshine for days or weeks. The resulting heat becomes more intense the longer a heat dome lasts.

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The intense heat began Tuesday in parts of California and the West. Sacramento, California, hit triple digits for the first time this year while Las Vegas ended up just a degree shy of its hottest temperature of the year so far. Numerous daily records were also broken in Texas.

Temperatures will soar higher on Wednesday across a larger portion of the Southwest. The most extreme heat will avoid major population centers along the coast, but Los Angeles will still be 5 to 10 degrees warmer than normal this week.

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Triple-digit temperatures will become widespread in California’s Central Valley Wednesday and stick around into the weekend. Conditions will also sizzle in Southern California’s desert regions.

Death Valley, the hottest place in the world, will likely reach a high temperature of at least 120 degrees by Thursday. Even the brutal desert landscape doesn’t typically get this hot until mid-to-late June.

Phoenix will likely hit 110 degrees for the first time this year by Thursday, even though the city doesn’t typically encounter these temperatures until mid-June. High temperatures are forecast to climb into the low 110s in Las Vegas, likely tying this year with 2010 for the earliest such reading on record in the city.

Summerlike heat will also send daily high temperature records tumbling. Phoenix; Las Vegas; Flagstaff, Arizona; Reno, Nevada; and Fresno, California, are just a handful of cities where the day’s high temperature record could fall on one or more days this week.

By Friday, records could be broken in parts of Oregon, Washington, Idaho and Colorado as heat expands north and east.

Deadly heat on the US-Mexico border

Dangerous heat isn’t new for the far southern US. Brutal heat in Mexico crept north into southern Texas earlier this spring and has been unrelenting for weeks. Several cities along the Texas-Mexico border experienced their hottest May on record.

The triple digit temperatures at the border proved deadly last weekend after US Border Patrol agents said four migrants died “from heat stroke and dehydration.”

The deaths were part of “several emergencies” involving heat-related illnesses last weekend, according to the US Border Patrol, El Paso Sector. The sector includes portions of southeastern New Mexico and western Texas.

Heat is the deadliest weather threat in the US. It kills more than twice as many people each year as hurricanes and tornadoes combined, according to the National Weather Service.

High temperatures in the area were about 5 degrees above normal from last Friday through Sunday, but are likely to climb to 10 degrees above normal Thursday and Friday.

Note: The CNN Original Series “Violent Earth with Liev Schreiber” explores harrowing weather events such as wildfires that are increasingly frequent in our changing climate. It airs on Sundays at 9pm ET/PT.

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