Power outages caused by windstorms on June 29 killed 26 people and are expected to persist through Saturday, says Risk Management Solutions (RMS).

This morning following Independence Day, Bloomberg reports that 500,000 customers in the mid-Atlantic region were still without electricity.

Thirteen states have been affected by the derecho, or squall line of fast-forming, long-lived, violent, convective (electrical) storms that travel hundreds of miles at speeds that may top 90 mph. The storms left four million without power in Maryland, Virginia, West Virginia, Washington, D.C., New Jersey and as far west as Iowa and Illinois early this week.

According to the National Oceanographic and Atmospheric Institute, a derecho produces destruction similar to that of a tornado, and can extend its reach of damage for more than 240 miles.

The storm system that produced the derecho began in Iowa on June 28 and threaded eastward with the National Weather Service Storm Prediction Center reporting high wind gusts picking up in 13 states. The highest wind speeds were reported at 91 mph at Fort Wayne International Airport, Ind., and at 81 mph at Tuckerton, N.J.

Barack Obama declared West Virginia a disaster area following the storm path, with 230,000 people still waiting to turn on their air conditioners and refrigerators.

Electric companies continue to work to get the power back on.

Exelon continues to experience disrupted service to 700,000 residents of its 4.3 million affected clients along the east coast, said the U.S. Department of Energy, and AEP/Appalachian Power said that 100 transmission lines were affected by the storm, although 80 percent of service has been restored to distribution stations. AEP Ohio may not fully restore power until July 10.

However, Bloomberg says Dominion Resources Inc., in Virginia, restored service to more than 95 percent of its 1 million customers that had lost power.