Extreme American heat wave breaks all-time hottest temperature record in March

Everything about this week’s record breaking western heat wave is extreme

By Andrea Thompson edited by Claire Cameron

On Wednesday in North Shore, California, temperatures soared to a blistering 108 degrees Fahrenheit (42 degrees Celsius) — matching the hottest March temperature on record for the state. And then, on Thursday, Phoenix, Arizona, hit 105 degrees F (41 degrees C) — the earliest such record by more than a month. And on the same day, temperatures just outside Martinez Lake, Arizona reached 110 degrees F (43 degrees C) – the highest March temperature ever recorded in the United States

The heat wave engulfing much of the western United States right now is unprecedented. An area of ​​high pressure – the strongest ever observed over the South West in March – ushered in the unusually fiery weather. This area, also known as a ridge because of the northward humps in the jet stream with which the phenomenon is associated, covers a huge swath of the United States. It will persist for several days, sending temperatures 20 to 30 degrees F (11 to 17 degrees C) above normal. It’s “one of the more meteorologically exceptional events I’ve seen in recent years in the American West, and that’s saying something,” climate scientist Daniel Swain said on his YouTube channel.

Generally, all record high temperatures in March tend to be set towards the end of the month, when it is climatologically warmer. But this heat wave is so extreme that it has broken some April records, never mind the ones for March. The event is “breaking records by … just absurd margins,” Swain said.

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“This is a summer-like ridge that occurs in March. It’s really shocking,” he added.

Ridges are always flanked by areas of low pressure, and the air at the surface flows from high to low pressure. It allows air in the atmosphere above to sink to the surface. As the air decelerates, it is compressed, which heats it up. The air under a hill is also stable, preventing the formation of clouds or rain showers – the clear sky allows sunlight to heat the surface unimpeded.

Another, conflicting weather pattern is also bringing the heat: a “Kona low” that drenched Hawaii in record-breaking rain last week. Essentially, when there is a lot of water vapor in the atmosphere, it represents potential – or latent – ​​heat. When that water vapor condenses and is wringed out of the atmosphere as intense precipitation (rain), it releases that heat. That’s what happened with the Kona lichen, and an atmospheric river now shunts that moisture and heat up into the Pacific Northwest, where some of it diverges into the ridge and likely increases the heat.

But climate change also plays a role. Research group World Weather Attribution, which does rapid analysis looking for climate change fingerprints on extreme weather, has said this heat wave would be “virtually impossible without climate change.”

In the last decade alone, such an event has become about four times more likely due to the heat trapped by greenhouse gases in the atmosphere and up to 0.8 degrees C warmer than it might otherwise have been.

Heat advisories and extreme heat warnings have been issued for many western states to warn of the health risks of heat, especially for the very young, older individuals and people who work outside – although summer temperatures often get much higher than this. The concern is not only based on the number on the thermometer, but also on the sudden heat. Normally, people have time to acclimatize gradually to warming temperatures throughout the spring and summer. But not now.

Read more: How to keep your home cool in extreme heat

Some experts are also concerned that the heat could provide ideal conditions for wildfires to spread. Much of the West is in a dry phase, and the snowpack that normally keeps soil and streams replenished with moisture in the spring is worryingly low. The heat wave will likely melt what’s left in “a shocking, sudden loss event,” Swain said on his YouTube channel. It will create even worse drought conditions and forest fire danger as the spring and summer continue.

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