Nighttime Heat Waves (image) University of Washington Caption Nighttime heat waves lasting three days or more in the Pacific Northwest between 1901 and 2009 are shown. The colors represent different ways of processing the historical readings. Credit K. Bumbaco, UW Usage Restrictions With credit Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.