June 17 (Reuters) – A grueling heatwave that has gripped the U.S. Southwest for three days spread eastward to Iowa and Missouri on Thursday, while punishing the hardest-hit areas with record high temperatures that are challenging local power systems. The National Weather Service issued excessive heat warnings for much of the Southwest, including Arizona, southern Nevada, much of California and parts of Utah. Heat advisories were issued parts of the Central Plains, including Kansas, Nebraska, Iowa and Missouri. “It’s a pretty big impact with respect to where the record heat is,” said National Weather Service meteorologist Bob Oravec at the Weather Prediction Center in College Park, Maryland. A high-pressure air mass parked across the Southwest has been bearing down for three days on the area where temperatures of around 100 degrees Fahrenheit (38 degrees Celsius) are not uncommon between now and September, Oravec said. “But now the temperatures in […]