The National Weather Service issued an excessive-heat warning for much of the US from North Dakota to the Mid-Atlantic states and into the South.<br/><br/>On Saturday, was another hot day in US as weather experts said the nation would experience warmer than normal temperatures for the rest of summer.<br/><br/>Meteorologists blamed the miserable conditions on a heat dome a stationary or extremely slow-moving high-pressure system in the upper atmosphere causing sweltering conditions on the ground below.<br/><br/>The excessive heat zone includes Philadelphia, where the Democratic National Convention will open on Monday.<br/><br/>