Unforgiving heat wave forecast in swaths of U.S. in the coming days

According to Heat.gov, the government’s heat portal, 108 million people are under heat alerts.

Heat indexes, a metric that gauges how much stress the heat and humidity will place on the human body, will be downright dangerous in many spots. Excessive-heat warnings blanket much of California, southern Nevada, western Arizona, Texas and Oklahoma, while heat advisories cover the surrounding areas, as well as part of Florida.

“Extreme heat and humidity will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities,” wrote the National Weather Service in Dallas.

Across the Southwest, meteorologists are warning that the heat risk is “extreme” and could have dire consequences, such as an “increase in heat-related illnesses, including heat cramps, heat exhaustion and heat stroke.” Heat stroke can quickly prove fatal. Excessive heat kills far more Americans annually than do hurricanes and tornadoes combined and disproportionately affects the elderly, the poor and other systemically vulnerable populations.

In some places, forecasters were even running out of ways to describe the severity of the heat.

“The atmospheric oven will roast and fry northern and central New Mexico like bacon through at least the next 7 days,” the National Weather Service in Albuquerque wrote.

Outside the South, parts of the southern Plains and Midwest are also sweltering. The peak heat index Wednesday is forecast to be 106 in Kansas City, Mo., and a blistering 112 in Topeka, Kan.

Why this heat wave is noteworthy

Heat is a staple of the summertime, but this heat wave is in a league of its own. In addition to the magnitude of the heat, enough to establish scores of new records, the temperatures are remarkable for their duration.

Phoenix, for example, has logged 12 consecutive days at or above 110 degrees, and the remainder of this week into early next is sure to bring the same. Daily highs are forecast to climb into the 115- to 118-degree range by late in the week and should carry into early next week, potentially posting its hottest week on record. In fact, there’s no immediate end in sight. That will surely establish a new city record for the longest streak of days to reach 110 degrees or higher; the current record is 18 days, set during June 1974.

El Paso is up to 26 days at or above 100 degrees, which is a new record, and in Miami, the heat index has hit 100 or higher for nearly a month.

The overarching weather pattern — featuring a sprawling heat dome, or stubborn ridge of high pressure — has been stuck for weeks. The heat dome deflects any inclement weather, and the jet stream, to the north. Beneath the dome, hot, dry, sinking air combines with ceaseless sunshine that bakes the ground.

That heat dome is expanding and now stretches from the eastern Pacific and the Baja Peninsula to Florida. By early next week it’s expected to expand northward and take hold of most of the country.

The Southwest

In the Southwest, the heat is dry but punishing. Phoenix isn’t alone in expecting absurd highs approaching 120 degrees. Las Vegas is likely to tie its all-time record high of 117 degrees on Sunday and Monday. If the city makes it to one degree higher, it would breach uncharted territory.

California’s Death Valley could approach or even nick 130 degrees this weekend, perhaps on Sunday. The National Weather Service is forecasting a high of 128 degrees at the Furnace Creek Visitor Center. A high of 130 degrees would match the mark it set on July 9, 2021, which is the highest reading ever reliably recorded worldwide, and would be hotter than anything experienced in the past 90 years. (There are some antiquated records that suggest Death Valley reached 134 degrees on July 10, 1913, but the measurement practices can’t be vetted.) The famously hot desert location might not dip below 100 degrees on Saturday, Sunday or Monday nights.

Across the rest of California, the worst of the heat looks to arrive on the weekend. Excessive-heat warnings have expanded into the central and southern San Joaquin Valley, where readings of 112 to 117 degrees could set a number of new all-time high temperature records. Excessive-heat watches have been posted for the northern Central Valley.

The National Weather Service in Hanford, Calif., estimates an 86 percent chance that Fresno hits 109 degrees on Sunday, an 81 percent chance for Bakersfield to reach that temperature and a 76 percent likelihood in Visalia.

“This type of heat will result in a major to extreme risk for heat-related illnesses for much of the population, especially those who are heat sensitive and those without effective cooling and/or adequate hydration,” the agency wrote.

It’s also worth noting that when the air is bone-dry anyone outside won’t notice the sweat gather on their skin, since it will immediately evaporate into the parched atmosphere. That means that people won’t realize they’re dehydrated until it may be too late.

Texas and the South

Widespread 102- to 107-degree readings will be the norm in Texas for each of the next several days. Combined with Gulf of Mexico humidity wafting northward, the heat index should push past 110 degrees for most residents of the Lone Star State.

It’s not just Texas that’s in the crosshairs of this brutal southern heat. Most of the mid-South, the southern Plains, the Gulf Coast and even the Southeast is in play. Dallas is looking at a heat index of 111 degrees on Monday, and Corpus Christi will feel like a mind-boggling 118 degrees. New Orleans, Memphis and Jacksonville, Fla., will also swelter with a heat index of 110 degrees.

The tropical humidity will prevent sweat from evaporating into the atmosphere, rendering the entire mechanism of evaporative cooling (the reason mammals sweat) moot and exacerbating our susceptibility to the extreme heat. As we sweat, we risk dangerous dehydration.

Dallas, Houston, San Antonio and Memphis are forecast to see actual air temperatures of 102, 100, 102 and 92 degrees, respectively. Many locations won’t fall below 80 degrees each night, a significant risk for the unhoused population who don’t have access to cooling shelters. There is a well-established link between premature deaths and warm overnight lows.

Florida

In Florida, the magnitude of the air temperatures alone is less impressive; highs are running just a few degrees above average. But a marine heat wave, with water temperatures off the southwest Florida coastline topping 95 degrees, is helping to pump robust moisture into the atmosphere.

That’s been combining with highs in the 90s to foster hazardous heat indexes. Miami, for example, had a heat index of 110 degrees on Sunday and Monday and 108 on Tuesday. A heat advisory remained in effect there Wednesday.

At least in Florida, the end is in sight. For days, a layer of Saharan air aloft was reducing thunderstorm chances, allowing sunshine to pour down unimpeded. That air mass has largely left, meaning that a return to daily storms and their cooling influence is likely in the days ahead.