Heat Wave and Storms Forecast for July Fourth Celebrations

Why it matters locally: Arizona is frequently impacted by extreme heat advisories, and the forecast for a national heat wave, especially around a major holiday, brings increased concern for public health and safety across the state.

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Millions of people across the United States are observing the 250th anniversary of the nation's independence during a period of hot weather. Twenty-one states have received extreme heat alerts as temperatures reach triple digits. Meteorologists are also tracking the potential for severe storms. These weather conditions could affect plans for holiday weekend activities across multiple regions. NBC News correspondent Sam Brock reported on the current weather patterns. Al Roker, a meteorologist for TODAY, provided updates on the holiday weekend forecast.