The National Weather Service issued a Severe Extreme Heat Watch for parts of Los Angeles County and adjacent ranges, in effect from June 18, 2026 at 10:46 until June 25, 2026 at 21:00. The alert covers multiple zones where dangerously hot conditions are possible, with highs near 100°F and peak heat anticipated on Wednesday and Thursday. Last update: June 20, 2026.
Officials said the watch signals an elevated risk of heat-related illnessparticularly for the very young, the elderly, people without air conditioning, and those active outdoors. Residents were advised to follow public safety guidance, seek cooled environments during the hottest hours, and call 911 in a medical emergency.
Affected areas and timing across Los Angeles County
The alert applies to the Santa Clarita Valleythe Western and Eastern San Fernando Valleyand the Los Angeles County San Gabriel Valley. Mountain and corridor zones included are the Western San Gabriel Mountains and Highway 14 Corridor and the Eastern San Gabriel Mountains. The watch remains in effect continuously through 21:00 on June 25, framing a multi-day period in which hazardous heat may develop, with conditions varying by location and elevation.
The expanded coverage from valley floors to adjacent mountains indicates a broad dome of high pressure capable of producing widespread hot afternoons and warm overnights that limit cooling. Authorities emphasized that the midweek period is the most likely window for the highest readings, though above-normal warmth may persist through the watch duration.
Temperature outlook and peak heat midweek
Forecasters noted temperatures up to 100°F are possible, with the hottest conditions expected Wednesday and Thursday. While local microclimates may modulate exact highs, the combination of elevated daytime heat and reduced nighttime relief can compound stress on vulnerable groups. Urban valleys could experience prolonged periods of high heat index values due to retained heat and limited ventilation.
Residents and workers in the affected valleys and mountain foothills were cautioned that even brief exposure during peak afternoon hours can lead to dangerous heat illness. Outdoor activities and strenuous labor should be adjusted when feasible, especially in sun-exposed areas with minimal shade or airflow.
Public health guidance and safety steps
Authorities urged frequent hydration, access to air-conditioned spaces, and regular checks on neighbors and relatives who may be at risk. People without adequate cooling were encouraged to identify cooling options and limit time in direct sun. Those engaging in outdoor work or recreation should pace activities, take breaks in the shade, and watch for symptoms such as dizziness, headaches, or nausea.
Emergency services advised that signs of heat stroke—including confusion, fainting, or lack of sweating—require immediate medical attention; call 911. Individuals were also reminded to never leave children or pets in parked vehicles, as interior temperatures can rise quickly even with windows cracked.
