Dangerous Heat for California and Desert SW Through Early Next Week

Summer 2022 is one that Pacific Northwest seasonal forecasters would like to have back. On the heels of a very wet and cool spring, and with La Nina conditions persisting in the Tropical Pacific, forecasters favored near or slightly below-average temperatures this summer. Instead, we’ve had well-above-average temperatures ever since late June, with an astonishing 12 days reaching 90 degrees or above. This ties 2015’s record, and there’s a chance we could touch 90 again today. A typical Seattle summer has only 2 such days.

The main story of this blog, however, is not the warmth in the Pacific Northwest, but the dangerous heat expected over California and the Desert SW later this week into early next week. Los Angeles could reach 100 degrees over the weekend, while the hottest spots of the Central Valley should top out in the low 110s. And with such hot weather over such a populated region, California’s power grid will see very high loads and Californians will likely be asked to conserve power during certain hours of the day. This blog will start with a brief discussion of the current and forecast conditions over the Pacific NW, and then will jump straight into the upcoming heat wave for California and the Desert SW.

Current Conditions: 

We currently have a large ridge of high pressure centered over the Inland Northwest. This ridge will bring well-above-average temperatures to the entire Pacific Northwest through the end of the week.

The National Weather Service has a Heat Advisory in effect for Seattle through Friday, but given the current model solutions, I wouldn’t be surprised if that Heat Advisory expires Thursday instead. As the chart below shows, Thursday and especially Friday should have stronger onshore flow than earlier this week, helping moderate temperatures west of the Cascades despite continued heat over the Columbia Basin. I’m currently forecasting Thursday and Friday to see highs in the low 80s across the Seattle metro area, with temperatures moderating into the 70s next week as onshore flow continues.

Later This Week: Dangerous Southwest US Heat

This ridge will migrate south as the week goes on, cooling temperatures over the Pacific Northwest but raising them over California and the Desert SW. This will result in near record temperatures for much of the Southwestern US, with Southern California experiencing its hottest temperatures of 2022.  Excessive Heat Warnings and Watches are already in effect through next Tuesday to cover the heat risk.

Unlike the current warm spell over the Pacific Northwest, the Southwest will experience hot, dry offshore flow. This will give 90-100 degree temperatures all the way to the Southern Californian Coast, with Los Angeles potentially experiencing a couple days in the low 100s from this weekend through early next week. Fresno should rise into the low 110s during the peak of the heat wave, and Death Valley may not see a high below 120 degrees until late next week!

While temperatures this high will certainly break daily records, they are not unprecedented for this time of the year. September is the second warmest month of the year for Los Angeles, and September 27, 2010 holds Los Angeles’ all-time high temperature record of 113 degrees. The reason for such a late peak in heat is because the intense heat and thermal low over the Desert SW earlier in the season causes onshore flow for Southern California, but when the days become shorter and the Desert SW cools off, offshore flow becomes much more common. The offshore flow with this heat event will be weak and shouldn’t result in additional downslope warming, but it will be strong enough to make it to the coast and keep the cool, marine air offshore.

The image below shows the warmest period of year on average for regions across the US (based on 1981-2010 climate normals). Note how nearly the entire West Coast – from Central Washington south to the Mexican Border – typically experiences their warmest period of the year after mid/late August. This is due to the increasing frequency and strength of offshore flow as the summer progresses into autumn.

Fire danger will increase throughout the week for California and peak this weekend/early next week when temperatures are hottest, the air is driest, and offshore flow is light-to-moderate in strength. I don’t expect the California utilities to call any Public Safety Power Shutoffs due to the marginal winds, but with such critical fire conditions over the area, it is imperative that we avoid new fire starts. Any new starts that occur during this heat wave could easily grow into much more destructive blazes when we start seeing the stronger “Santa Ana” and “Diablo” winds that routinely impact California in the autumn.

Load Forecasts and the California Power Grid

Due to this heat being centered over the major population centers in Southern California, loads on California’s grid are expected to be extremely high. The chart below shows the net load forecast for California over the next seven days – note how net loads are expected to peak near 47,000 MW from Sun 9/4 to Tue 9/6. These would be the highest loads experienced thus far this year.

Because California is in the midst of a multi-year drought, they don’t have much hydropower to work with on their own system, and while they can import power from other areas, there are still constraints in how much power can be sent over the transmission lines feeding into California’s system. The California ISO will almost certainly issue one or more “Flex Alerts” – which are announcements asking the public to conserve electricity during peak hours. This could involve reducing the power usage during peak hours, or it could involve scheduling a power-intensive task (such as running a dishwasher or charging an electric vehicle) to lower demand hours.

Due to high heat and forecasted energy demand across the state, the power grid operator issued a Heat Bulletin to prepare consumers for #FlexAlerts, especially on 9/4 & 9/5. https://t.co/kVLNk4w3l5

— California ISO (@California_ISO) August 31, 2022

The latter is a form of “demand response,” where power demand is not reduced but is “shifted,” so that peak loads are reduced. Demand response is one of the cheapest and most efficient ways to reduce greenhouse gas emissions, as the lower, stabler demand results in lower and less volatile energy wholesale energy prices, making it uneconomical to bring inefficient natural gas or diesel “peaker” plants online to cover peak loads. There are a lot of pieces to the decarbonization puzzle, but demand response is a massive one that doesn’t get nearly as much attention as renewable energy, and it will only become a bigger factor as battery technology progresses, renewables penetration increases, and the grid becomes more connected at the distribution level.

Enjoy the warmth here in the Pacific Northwest, but prepare for heat and California ISO Flex Alerts if you live in the Golden State.