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Extreme Heat Watch San Bernardino County Mountains: What to Know Tuesday–Friday

By CALWIRE Weather Desk — Saturday, August 22, 2026
By CALWIRE Weather Desk  |  PUBLISHED: Saturday, August 22, 2026
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Photo: Omnitrans Joint Powers Authority / Public domain

A potentially life-threatening heat event is bearing down on the San Bernardino County Mountains, with an extreme heat watch now in effect from Tuesday through Friday, according to early reports. Temperatures across Southern California are already soaring past 100 degrees, and conditions in the mountains could make this stretch especially dangerous for residents and visitors alike.

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The watch covers the mountain communities of San Bernardino County specifically, setting it apart from the broader heat advisories already issued for other parts of Southern California. Extreme heat watches at this level are not routine, and forecasters are flagging the risk as serious. This story is developing, and the exact temperature projections and geographic boundaries may be updated as the week progresses.

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If you're in San Bernardino County, don't wait on this one. Check on neighbors, especially older adults and anyone without reliable air conditioning. Hydrate early, limit time outside during peak afternoon hours, and know where your nearest cooling center is before the heat peaks.

What We Know So Far

Southern California
Southern CaliforniaPhoto: apnews.com

The extreme heat watch runs Tuesday through Friday for the San Bernardino County Mountains. A separate heat advisory has been issued for other parts of Southern California. Temperatures regionwide have already pushed past 100 degrees, per KTLA and CBS News reports. Details on exact peak temperatures and specific mountain communities affected have not yet been confirmed in early reports.

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Why Mountain Communities Are at Risk

Mountain areas don't always have the cooling infrastructure that valley cities do, and residents there may be less accustomed to extreme valley-level heat. Overnight temperatures that don't drop much can make conditions harder on the body, and power grid strain is always a concern during multi-day heat events like this one.

Stay Updated

This is a developing story. Conditions, watches, and advisories can be upgraded or expanded quickly during an active heat event. Follow the National Weather Service and San Bernardino County emergency management for the latest alerts as Tuesday approaches.

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Filed Under: Weather Extreme Heat Watch San