A punishing heatwave, known as the "heat dome," that originally swept through Mexico in May is now expanding northward into the western United States, raising concerns of record-breaking temperatures from Arizona to the Pacific Northwest. This week, California's interior is expected to experience some of the most intense heat, with Wednesday, Thursday, and Friday predicted to be the hottest days, with temperatures at least 10 to 20 degrees above normal.

The region is bracing for scorching conditions, with temperatures ranging from 100 to 110 degrees anticipated in much of the interior West. Even more extreme temperatures are expected in desert locations, where readings could top 110 or even 120 degrees in the most extreme cases. Meteorologists are predicting that dozens of record highs will be shattered as the heatwave takes hold.

As a result, several areas are already under excessive heat watches and warnings, including much of interior California, southern portions of Arizona and Nevada, as well as southern Utah. Major cities such as Las Vegas, Sacramento, and Phoenix are among the locations affected by these heat alerts, impacting approximately 25 million residents. The number of affected individuals is expected to grow as the heat reaches its peak later this week.

The Desert Southwest will experience the most extreme heat, with warnings set to take effect on Wednesday for cities such as Phoenix, Las Vegas, and Death Valley. Heat warnings also extend to California's Central Valley, including Bakersfield, Fresno, and Sacramento, with the warning even reaching as far north as Shasta County and Redding. Heat advisories are in effect even closer to the coast, including eastern portions of the San Francisco Bay Area.

The National Weather Service's HeatRisk product indicates that the Southwest and California's Central Valley will experience "major" impacts from the heatwave, graded as Level 3 out of 4, from Wednesday through Friday. Some smaller pockets within southeastern California and southern Nevada may even face "extreme" or Level 4 conditions on Thursday and Friday.

Record warmth is expected to transition from isolated occurrences on Monday to widespread and persistent heat by Thursday. For instance, Las Vegas is forecasted to reach 108 degrees on Wednesday, just one degree shy of breaking the June 5 record. Predictions of 111 and 110 degrees on Thursday and Friday, respectively, would establish new calendar-day records. Nighttime lows are also alarming, as Las Vegas may only dip into the mid-80s later this week, posing additional risks.

In the Desert Southwest, temperatures are set to surpass 110 degrees easily, with Phoenix expected to set a record high of 112 degrees on Thursday, while Needles in California's eastern region may reach 114 degrees. Notorious for its extreme heat, Death Valley is likely to experience temperatures exceeding 120 degrees on multiple days during this period. If Death Valley reaches 124 degrees, it would mark the highest temperature recorded so early in the season.

Moving northward, the heatwave will soon impact California's Central Valley, with numerous locations potentially breaking records by Wednesday as temperatures exceed 105 degrees. By Thursday, Northern California will experience record-challenging heat, followed by a brief period of extreme temperatures reaching the Pacific Northwest on Friday.

According to the National Weather Service, what makes this heatwave exceptionally dangerous is not only the high afternoon temperatures but also the lack of relief at night. A persistent heatwave early in the year is a cause for concern as people are not yet acclimatized to the intense heat. Lack of proper shelter and air conditioning further exacerbates the risks associated with such extreme heat, potentially leading to heat-related fatalities.

This heatwave coincides with the overall trend of increasing temperatures globally, with each of the past 12 months setting record highs. Recent incidents of near-record heat in India and Iraq, as well as repeated episodes of heatwaves in South Florida and southern Texas, highlight the severity of the current situation. As human-caused climate change intensifies, these extreme heat events are likely a preview of even more severe conditions to come.

Although the heat is expected to ease slightly over the weekend, above-normal temperatures are projected to persist in the Western US until at least mid-June. Authorities urge residents to remain vigilant, stay hydrated, and seek shelter in air-conditioned spaces to mitigate the health risks associated with the ongoing heatwave.