July 2024 was the all-time hottest on record for many Bay Area locations. Here's why

It was an extremely hot July in the Bay Area with many locations observing the all-time hottest July on record.

The average July temperature is calculated by taking the average of both daytime and nighttime temperatures in specific locations. A big factor was not only the very hot daytime highs but that there was not much relief in terms of cooler overnight lows.  

Inland East Bay communities like Concord and Livermore observed average July temperatures in 2024 in the mid to upper 70s - around 5 degrees or more above normal for the month and breaking the old record by 1-2 degrees.

North Bay communities felt average temperatures in the mid to upper 70s were well over 5-6 degrees above normal and broke the old record heat by over 2 degrees.

Locations in the Santa Clara Valley may have been slightly cooler, in the mid-70s, but compared to normal that's over 7 degrees warmer than it should be for July. Those temperatures broke the old record by over 2 degrees.

Mt. Hamilton felt an average July temperature of 79.7, over 8 degrees above average and breaking the old record by 2 degrees. 

But the most staggering observation site was Skyline Ridge in the Santa Cruz Mountains.

The average temperature for that site was nearly 82 degrees, over 12 degrees above normal for July, which shattered the old record by nearly 7 degrees.

The hotter-than-normal temperatures at Skyline Ridge may seem odd, especially since it was hotter than the other observation sites, but it was due to a particular weather phenomenon.

The reason for the excessive heat, in general, was a persistent pattern of high pressure that sat over the West Coast, also known as a 'Heat Dome'.

The 'Heat Dome' did not budge for weeks on end in July, which is why many locations also broke daytime high temperature records for multiple individual dates during the month. The high pressure also blocked the onshore flow from being nearly as strong or persistent.

Much of the month lacked the iconic 'No Sky July' look without the dense fog and sea breeze.

A lot of the time, the 'Heat Dome' was centered farther south, which is why places south of the Bay Area broke their records by even more. It's the reason Skyline Ridge was so much hotter — It's on the southern edge of Bay Area, where the 'Heat Dome' was more directly overhead.

Luckily, August will not be nearly as hot as the 'Heat Dome' has departed, no longer centered directly over the West Coast. This has allowed the stronger onshore flow normally seen this time of year, bringing in the fog, to persist across the Bay Area.

 Long-range models are also pointing to a more seasonable, if not slightly cooler, pattern sticking around through late August.