Wednesday, December 15, 2021
A persistent July heat dome has put more than 100 million people under heat alerts, driving temperatures past 110 degrees from the Southwest into the northern Plains.
A sprawling dome of high pressure has locked dangerous heat over much of the country. By the weekend of July 25 more than 100 million people were under heat alerts from the National Weather Service, from the desert Southwest to the northern Plains. The same ridge that broke all-time records across Montana and Wyoming in mid-July, when Miles City reached 115 degrees, has since spread south and east into the Rockies, the central Plains, and the Upper Midwest.
The readings have been punishing. As of July 26, forecasters expected Las Vegas near 112 degrees, Phoenix near 109, and Rapid City, South Dakota, close to 105 after the city hit 112 the day before. Denver, Omaha, Dallas, and Kansas City were all forecast to pass 100. Heat index values of 105 to 115 degrees covered a broad area. Those numbers climb through the afternoon, so any single figure is a floor rather than a final reading while the pattern holds.
Heat is the deadliest kind of weather in an average year, and it does its damage quietly. The body loses the ability to cool itself well before most people feel they are in real trouble. Drinking water before you feel thirsty is the habit that matters most, and keeping up with survival hydration through the day beats trying to catch up once a headache sets in. Move hard outdoor work to the early morning, and treat the hottest hours as time to stay indoors and still.
A cool home is the other half of the job. Holding indoor temperatures down gets harder when the grid is strained, and preparing your home for extreme heat covers how to shed heat when the power is on and how to hold it out if the power fails. That failure is a real risk this week, because air conditioners run flat out and demand spikes toward evening, so it helps to know how to prepare for a power outage before the grid is tested. Check on the people who feel heat first, since older adults, young children, and anyone without air conditioning are the ones a hot week reaches soonest.
Where it stands now, a cold front should ease the Upper Midwest early in the week, but dangerous heat is expected to hold across the central and southern states for days. Heat domes break slowly. Find your nearest cooling center before you need it, keep water within reach, and do not count on the overnight low for relief when it only falls into the 80s.
