Intense Southern California Heat Wave Shatters All-Time Record Highs

The eastern two-thirds of the United States has been mired in an oppressive heat wave for the past couple of weeks, bathing much of the country in a brutal mix of hot temperatures and high humidity. However, while the east has gotten all the headlines (as usual), it's not the only heat in town. The desert southwest and southern California are in the midst of their own historic heat wave, the likes of which have never been recorded in some cities. The heat in the west has more than made up in intensity what it lacks in longevity.

Temperatures easily climbed into the 100s across much southern California and the state's Central Valley, and readings pushed 120°F in the California and Arizona deserts. Downtown Los Angeles reached 108°F on Friday. San Diego saw a high of 96°F. Yuma, Arizona, set a daily record high of 117°F. Las Vegas reached a toasty 112°F—a few degrees short of a record, sure, but still 8°F above normal.

You would expect this type of heat in the desert, but many spots in urbanized areas of California set record highs on Friday. Some of those cities saw their warmest July day on record, and some reporting stations even saw the hottest day ever recorded in decades of weather observations. At least six reporting stations in southern California on Friday broke their all-time record highs.

• Burbank Airport, which is east of downtown Los Angeles, saw a high temperature of 114°F on Friday afternoon. This broke the all-time record high of 113°F set there in September 1971.
• UCLA, which is in western Los Angeles, saw its all-time record high of 111°F on Friday, beating the previous record of 108°F set all the way back in September 1939.
• Van Nuys Airport, northwest of downtown Los Angeles, measured a 117°F high on Friday. The previous all-time record high at the airport was 114°F—however, the airport's records only go back 24 years.
• Riverside, California, reached 118°F on Friday,  tying the all-time record high first set there back in July 1925.
• The fire station in Santa Ana, California, south of Anaheim, measured a high temperature of 114°F on Friday afternoon. This was the hottest temperature ever recorded in Santa Ana, where records go back to 1893. The previous all-time record high was 112°F set in June 1917.
• The airport in Ramona, California, northeast of San Diego, saw an all-time record high temperature of 117°F on Friday. While impressive, records here only go back to April 1998.

The cool water of the Pacific kept communities immediately along the coast much cooler than spots just a few miles inland, but the air was considerably hotter just a few thousand feet above ground level. It was still hot at the surface despite the marine layer's powerful influence. Los Angeles International Airport only ("only") reached 92°F on Friday, but that still beat the record high of 88°F for July 6 set back in 1957.

Temperatures will climb back up into record territory for many of the same areas on Saturday. The heat will start to break on Sunday and should fall back to simply above-normal through early next week.

Why is it so blazing hot? There's a large and powerful upper-level ridge over the western half of the United States. Ridges are associated with sinking, stagnant air; we saw a great example of this last week when several derechos rode around the ridge over the Plains. There are also localized factors at play, such as downsloping winds off of higher terrain (air warms as it descends) and the classic urban heat island effect.

This type of heat is more common of early fall than the middle of summer. Our traditional idea of weather fitting neatly into three-month seasonal blocks kind of falls apart once you travel west of the continental divide. The brutal heat of summer usually plagues southern California once September rolls around, as evidenced by Burbank and UCLA's all-time record highs falling in September.

This is typically the dry season across southern California. Cities like Los Angeles historically see very little rainfall between the end of May and the end of September. Much of southern California has slipped into a moderate to severe drought over the past couple of months. These brutally warm temperatures won't help the cause. Extreme heat helps remove moisture from the ground even faster than normal, which could exacerbate dry conditions heading through the rest of the summer.

[Weather Model: Tropical Tidbits | Temperature Map: me]

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