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From Phoenix to Sacramento, West sweats through worst heat wave in decades

Children cool off from the intense heat in in the Grand Park water fountain in downtown Los Angeles on Monday, June 20, 2016. As the mercury rose on Sunday, records fell and the National Weather Service reported 17 daily heat records were broken in Southern California with more of the same in the works for Monday because of a high pressure over the Four Corners region of the Southwest. (Richard Vogel / Associated Press)
By Angela Fritz Washington Post

All-time heat records could be in jeopardy in the Southwest this week as a dome of hot, high pressure settles over the region. Triple-digit highs are in the forecast from Arizona to Northern California – including the Sierra Mountains.

Notably, this heat wave is going to last through the week, which raises concerns of heat-related illness. Excessive heat warnings are in effect across the southwest, and the National Weather Service doesn’t plan to drop them until Friday.

Phoenix hit 90 degrees at 7 a.m. Monday morning, and they’re shooting for a high around 116. Highs on Tuesday will rival the city’s all-time record – 122 degrees. Phoenix has only reached 120 degrees on three occasions at Sky Harbor airport, and the last time was 20 years ago.

“Heat of this magnitude is rare, dangerous and very possibly deadly,” the Weather Service in Phoenix warned on Monday.

Records were set in California on Sunday as the temperature rose to triple digits in the Central Valley. The high temperature was 97 degrees at San Francisco International, which set a new record for the date – one degree shy of the warmest temperature ever in the month of June. Hayward Airport climbed to 100 degrees, breaking the old record for the date by a whopping 13 degrees.

In Sacramento, the temperature is expected to climb above 100 every day through Saturday. If that happens, it will be nine consecutive days of triple-digit heat, which is the June record for the city, according to the National Weather Service. That hot streak happened in 1981.

This heat wave is right on time. In the weeks leading up to the beginning of monsoon season, temperatures in Arizona, New Mexico, southern Nevada and Southern California typically climb to the highest they’ll be all year.

Southwest Monsoon, which occurs annually, is actually triggered by the very heat looming in the forecast early next week. The buildup of warmth creates a large-scale trough of low pressure that extends from Mexico to Arizona, Southern California and Nevada. Air flows away from high pressure and toward low pressure, so moisture is drawn over the Southwest.

Tucson, for example, experiences its wettest months in July and August, although the monsoon can last through September.

The reason it can get so hot in the Southwest is that the humidity is so low. Perhaps it’s counterintuitive, but in the eastern United States – where summer humidity can be oppressive – the presence of moisture in the air keeps the temperature down. In the Southwest, there’s no moisture in the ground for the sun’s energy to evaporate. So, instead, it goes toward making the air hotter and hotter.

The best thing you can do during a heat wave like this is stay indoors. If you’re working outside, take frequent breaks to rehydrate and cool your body. You may not realize you’re overheating, because sweat evaporates instantaneously in such dry conditions, but you can quickly suffer from heat stress in these conditions.