![]() ![]() When you’re excessively warm, you tend to build and strengthen the anticyclone, which encourages continuation of clear skies, which in turn encourages a lack of precipitation, which makes it drier, which makes the incoming solar radiation more able to heat the ground.” Heat waves threaten the power grid just as people need electricity the most. “It compounds on itself,” said Jonathan Martin, a professor of atmospheric science at the University of Wisconsin Madison. But with so little water in the ground, in waterways, and in vegetation, there isn’t as much to soak up the heat besides the air itself. Moisture in the ground can blunt the effects of heat, the way evaporating sweat can cool the body. Heat waves are especially common in areas that are already arid, like the desert Southwest, and at high altitudes where high-pressure systems readily form. The ground - soil, sand, concrete, and asphalt - then bakes in the sunlight, and in the long days and short nights of summer, heat energy quickly accumulates and temperatures rise. The high-pressure system also pushes out cooler, fast-moving air currents and squeezes clouds away, which gives the sun an unobstructed line of sight to the ground. The sinking air acts as a cap or heat dome, trapping the latent heat already absorbed by the landscape. That creates a sinking column of air that compresses, heats up, and oftentimes dries out. Heat waves begin with a high-pressure system (also known as an anticyclone), where atmospheric pressure above an area builds up. The impact of this additional exposure to solar radiation is cumulative, which is why temperatures generally peak weeks after the longest day of the year.Īmid the general increase in temperatures in the summer, meteorology can push those numbers to extremes. So the threshold for a heat wave in Tucson is higher than the threshold in Seattle.ĭuring the summer in the Northern Hemisphere, the northern half of the planet is tilted toward the sun, which increases daylight hours and warms the hemisphere. ![]() What counts as a heat wave is typically defined relative to local weather conditions, with sustained temperatures in the 90th to 95th percentile of the average in a given area. Heat waves, explainedĮxtreme heat might not seem as dramatic as hurricanes or floods, but the National Weather Service has deemed it the deadliest weather phenomenon in the US over the past 30 years, on average. ![]() But with global average temperatures continuing to rise, more records are poised to fall. With a large El Niño warming pattern brewing in the Pacific Ocean, 2023 may be one of the hottest years on record. They’re a public health threat that can exacerbate inequality, cause infrastructure to collapse, and amplify other problems of global warming. The forces behind them are complex and changing. There’s more to heat waves like this than high temperatures, though. Scientists say these record highs align with their expectations for climate change, and warn that more scorchers are coming. It has stressed the power grid and caused outages just as people most urgently needed to cool off. A deadly heat wave is broiling Louisiana, Texas, and Mexico this week with record-breaking temperatures reaching 114 degrees Fahrenheit. ![]()
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