Iowa's largest electrical utilities will participate next week in a national exercise to test U.S. response to a simulated prolonged blackout. The exercise will test vulnerabilities of the power grid to attack, The Des Moines Register reported. Officials with MidAmerican Energy Co. and Alliant Energy confirmed they will be involved in the exercise, called GridEx II,  Nov. 12-13. The event is sponsored by the North American Electric Reliability Corp., a nonprofit entity whose mission is to ensure the reliability of the bulk power system in North America. The scenario calls for a simulated "prolonged blackout" that will highlight timely vulnerabilities and issues facing the electrical utility industry.