Soaring temperatures across the U.S. strained power grids, snarled commuter traffic, and caused at least 10 deaths this week. Temperatures hit 110 degrees in Redding, in Californias Central Valley, and hovered in the 90s as far north as Maine. A 3-year-old boy died of heatstroke in Indiana after he accidentally locked himself in a car while playing. In New York City, where temperatures hit a record 98 degrees, service was shut down on one subway line after rails buckled in the heat. Violent thunderstorms brought cooler air to the Northeast, but it may be a week or more before the Southern U.S. gets any relief.