Why is there a heatwave on the West Coast?

There is a significant heatwave on the West Coast of the United States on July 5, 2024, primarily due to a strong upper-level high-pressure system, also known as a heat dome (1)(2)(3).

This weather pattern traps hot air in the region, leading to prolonged periods of extremely high temperatures. Human-caused climate change has also increased the frequency and intensity of such heatwaves.

Which cities or areas are affected by the heatwave?

The heatwave is affecting a widespread area of the western United States. Cities and areas affected by the heatwave include:

• Arizona: Phoenix
• California: Los Angeles, San Francisco, Sacramento, Redding, Death Valley
• Idaho: Boise
• Nevada: Las Vegas
• Oregon: Portland, Medford
• Washington: Seattle

Heatwaves can lead to more numerous, intense, and widespread wildfires. There are currently significant fires in Butte County (Thompson Fire) and Mariposa County (French Fire) California.

There is a heat advisory for much of the U.S. South and Mid-Atlantic states and a smaller excessive heat warning impacting parts of Maryland, North Carolina, and Virginia (4).

How long will the heatwave last?

The heatwave began intensifying around the start of July and is expected to peak from Friday through Monday, lasting through at least the middle of the following week. This prolonged period of high temperatures could last up to ten days, making it one of the most extended heatwaves in recent history.

Are there any alerts in place?

Numerous heat alerts, including excessive heat warnings and advisories, are in place across the affected regions. Red flag warnings have been issued due to elevated wildfire risks.

Evacuation orders are active in areas impacted by wildfires, such as Butte County for the Thompson Fire and Mariposa County for the French Fire.

Cooling centers have been opened, and residents are advised to stay indoors, stay hydrated, and follow safety precautions to mitigate heat-related health risks.