California braces for 110°+ heat wave: All 28 active alerts this Thursday

California is facing widespread extreme heat warnings and heat advisories this Thursday, August 21st, with alerts stretching from the Central Valley to the deserts of Southern California.

Record-breaking temperatures are expected across valleys, deserts, and inland areas, while Red Flag Warnings highlight an elevated risk of wildfire due to hot, dry, and unstable conditions.

Quick Guide: Heat Alerts in California (August 21, 2025)

For a clear picture of the scale of the heatwave, here’s a quick guide to every official alert in effect today.

California’s inland regions are bearing the brunt of the heat, with the Central Valley, deserts, and interior mountains all under some form of warning. Some alerts, like those in the Siskiyou County valleys, will stretch into next week, while others are expected to ease after Saturday evening. The overlapping Red Flag Warnings add another layer of concern, with hot, unstable air and gusty winds raising wildfire risks.

Statewide Overview

A total of 28 active alerts are in place across California as of this morning. The warnings have been issued by multiple National Weather Service offices, including Hanford, San Francisco, San Diego, Los Angeles/Oxnard, Eureka, and Sacramento, with additional coverage from regional offices in Medford (OR), Reno (NV), Las Vegas (NV), and Phoenix (AZ).

Most alerts remain in effect through Saturday, August 23, with some extending into Sunday, August 24 or later, depending on location.

Extreme Heat Warnings

The most serious alerts in place today are Extreme Heat Warnings, covering wide areas of California’s valleys, deserts, and foothills. These warnings indicate dangerous temperatures that significantly increase the risk of heat-related illnesses.

• San Joaquin Valley & Foothills (Hanford CA): Highs between 105–110°F, with warm overnight lows in the 70s and 80s providing little relief.
• Mojave Desert & Indian Wells Valley: Temperatures expected to reach 105–110°F.
• San Diego Deserts, Coachella Valley, San Gorgonio Pass: The hottest zone in the state, with temperatures climbing as high as 116°F.
• Apple & Lucerne Valleys: Conditions reaching up to 108°F.
• Death Valley, Owens Valley, Mojave regions (Las Vegas NV coverage): Among the hottest in the country today, with highs ranging from 105–120°F, including Furnace Creek near 120°F.
• Southwest California (Los Angeles County, San Fernando Valley, Santa Clarita Valley, Ventura County Mountains, and nearby regions): Temperatures ranging 95–110°F, impacting both urban and rural communities.
• Siskiyou County Valleys (Weed, Yreka, Happy Camp): Highs of 100–110°F through early next week.
• Imperial & Southeast California Deserts (Phoenix AZ coverage): Dangerous heat with highs between 107–116°F.

Heat Advisories

In addition to the most severe warnings, a wide swath of California is under Heat Advisories, which signal conditions that can still cause heat stress and illness, especially for vulnerable populations.

• Central Valley (Merced, Fresno, Tulare, Kern): Temperatures reaching up to 107°F across key agricultural areas.
• Bay Area & Central Coast (Santa Clara Valley, East Bay, North Bay, Monterey & San Benito Counties, Santa Cruz Mountains): Highs in the 90s to low 100s, with slightly cooler nights near the coast offering modest relief.
• Northern California (Trinity, Humboldt, Lake, Mendocino, Shasta, Sacramento Valley): Daytime highs between 95–110°F, extending heat risk into traditionally cooler inland counties.
• Southern California (Inland Empire, Orange County, Mountains, San Diego Valleys): Broad coverage with temperatures between 96–108°F, depending on elevation and location.

Red Flag Warnings (Fire Weather Risk)

Alongside the extreme heat, Red Flag Warnings remain in effect, underscoring the heightened wildfire danger.

• Kern County (Frazier Park, Grapevine): Low humidity and gusty winds, combined with a chance of dry lightning, make fire starts more likely and difficult to control.
• Los Angeles, Ventura, Santa Barbara, San Luis Obispo Counties (mountains & foothills): An unstable air mass and unseasonable heat are combining to create conditions favorable for rapid fire growth through at least Saturday evening.

Health & Safety Guidance

Officials warn that heat-related illnesses such as heat exhaustion and heat stroke can develop quickly under these conditions. Key safety steps include:

• Stay hydrated: Drink plenty of water and avoid alcohol or caffeine, which can worsen dehydration.
• Keep cool: Spend time in air-conditioned spaces when possible, and use fans or cooling centers if home cooling is limited.
• Limit outdoor activity: Schedule strenuous work or exercise for early morning or evening hours.
• Check on others: Older adults, children, outdoor workers, and those without adequate cooling are at highest risk.
• Vehicle safety: Never leave children or pets in parked cars — interiors can become lethal within minutes.

The National Weather Service also reminds residents that overnight lows in the 70s to 80s across much of inland California mean that relief from the daytime heat will be minimal.

Stay Cool; Stay Safe; and Stay Informed

California is under one of the most widespread heat alert events of the summer, with both Extreme Heat Warnings and Heat Advisories in place across nearly every inland region. Added Red Flag Warnings further elevate wildfire risk as the state moves into a dangerous late-August weekend.

Residents are urged to stay cool, stay hydrated, and stay informed by monitoring official National Weather Service updates and local advisories.