Heat Advisory Issued for Northern Californias Mendocino and Lake Counties as Temperatures Reach 100-110F

When the sun was already blazing over northern California on Saturday night, the National Weather Service (NWS) office in Eureka sounded the alarm.

At 9:33 p.m., the NWS issued a heat advisory that will remain in effect until Sunday at 10 p.m. The warning covers Northwestern Interior Mendocino, Northeastern Interior Mendocino, southeastern Interior Mendocino, Western Lake, Southwestern Lake, Eastern Lake, and the entirety of Lake County.

Officials forecast temperatures of 100 to 110 °F for Sunday, a range that the NWS classifies as a moderate to major HeatRisk. The agency cautions that hot conditions are likely to persist throughout the day and that heat‑related illnesses could arise.

To stay safe, residents are urged to drink plenty of fluids, seek refuge in air‑conditioned rooms, and avoid direct sun exposure. The NWS also reminds people to check on vulnerable neighbors and relatives, and to never leave young children or pets in vehicles—car interiors can reach dangerous temperatures in minutes. Outdoor workers should follow Occupational Safety and Health Administration (OSHA) guidance, which calls for regular rest breaks in shaded or air‑conditioned environments and immediate transfer of anyone affected by heat to a cool area. In an emergency, the NWS says people should call 911.

Heat advisories are issued when the HeatRisk level reaches Level 2 on the NWS HeatRisk scale. The scale ranges from 0 to 4, with higher numbers indicating greater risk of heat‑related health problems. A Level 2 rating means that temperatures are high enough to pose a moderate to major risk to people who are not acclimated to the heat.

The advisory also reminds people to recognize warning signs of heat exhaustion and heat stroke, to wear lightweight and loose‑fitting clothing, and to time strenuous outdoor activities for early morning or evening when temperatures are lower.

The NWS is part of the National Oceanic and Atmospheric Administration (NOAA), a branch of the U.S. Department of Commerce. Its local weather forecast offices, such as the one in Eureka, issue advisories, watches, and warnings to protect the public from hazardous weather conditions.

Mendocino County, located on California’s north coast, has a population of about 91,000 people, according to the 2020 census. Lake County, directly north of the San Francisco Bay Area, has a population of roughly 68,000. Both counties are known for their wine production and natural landscapes, but the heat advisory highlights that even rural and scenic areas can experience dangerous heat conditions.

Residents in the affected regions are urged to follow the NWS guidance and to stay informed through local news outlets and the NWS website. The advisory will remain active until Sunday night, after which the NWS will reassess conditions and issue any further updates as necessary.

The heat advisory is part of a series of NWS heat advisories issued across Northern California during the summer of 2026. For example, a heat advisory issued on August 5 covered Central Siskiyou County and Western Siskiyou County. These advisories aim to reduce heat‑related health risks across the region. Residents should heed the guidance and stay safe.