Cold, dry Arctic air moving across the central and eastern US early next week will cause temperatures to drop to 10-15 degrees below average, according to the Weather Prediction Center. The chilly forecast is causing natural gas prices to spike, as the demand for heating fuel increase,s as it normally does this time of year. Natural gas now provides about 40% of US electricity. U.S. natural gas futures on Monday climbed above $4.30 per MMBtu, the highest since March. The colder forecast is one factor behind the price rise; the…