A national heat wave has Americans dripping in sweat from San Diego to Boston and the strain on the electrical grid is causing power outages. Record amounts of electricity are being used today, and air quality in some regions is reaching unhealthy levels.

In the Midwest, about 300,000 customers have been without power in Wisconsin and Michigan. In New York City, outages shut down parts of LaGuardia Airport and the subway system during the morning rush hour.

Air quality is poor throughout the mid-Atlantic states, with smog so bad that it reached the "purple zone," which is one level past red. The rarely used classification means that it's unhealthy for anyone to spend much time outdoors.

The Midwest and Northeast states are expected to get a break soon from the heat: A cold front is forecast to move in from Canada, and thunderstorms are possible along the Atlantic states.

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