What Is An Extreme Heat Warning Today

What Is an Extreme Heat Warning Today?

An Extreme Heat Warning is a public alert issued by the National Weather Service (NWS) when forecasted heat index values are expected to reach dangerous levels for an extended period. The warning signals that the combination of high temperature and humidity will create conditions that can quickly lead to heat‑related illnesses such as heat exhaustion, heat stroke, or even death, especially for vulnerable populations.

How the NWS Determines an Extreme Heat Warning

The NWS typically issues an Extreme Heat Warning when:

• The heat index is forecast to reach 105 °F (40.6 °C) or higher.
• The elevated heat index is expected to persist for at least two consecutive days.
• Local factors—such as urban heat islands or limited nighttime cooling—increase the risk of prolonged exposure.

These criteria may vary slightly by region, but the core purpose remains the same: to encourage the public to take immediate protective actions.

Current Situation: A Valley Heat Wave

KTLA’s Chris Wolfe reports that the Los Angeles Valley is experiencing a dangerous heat surge. Highs will be near or above 100° for at least Thursday, Friday and Saturday, pushing the heat index into the extreme range across much of Southern California. The forecast aligns with a broader pattern of heat waves that have already impacted Phoenix, where temperatures have consistently topped 110 °F for several days.

Here’s a recap of the day and what the next few days look like in and around the Valley:

1. Thursday: Morning lows in the mid‑70s, but afternoon heat indices climb to 112 °F.
2. Friday: Slightly higher nighttime lows (mid‑80s) keep the heat index above 115 °F.
3. Saturday: Expect another peak near 115 °F, with limited relief after sunset.

The prolonged heat has prompted the NWS to issue an Extreme Heat Warning for the entire region, and local officials are urging residents to stay indoors, hydrate, and check on neighbors.

Why the Warning Matters

When temperatures exceed 100 °F, the body’s ability to cool itself through sweating becomes less effective, especially when humidity is high. The resulting heat index—often called the “feels‑like” temperature—can be 10–30 °F