While we're on the topic of tornados... Here is a pic of the tornado that hit La Plata, MD earlier this year. This picture is taken from Calvert Cliffs nuclear plant - thats how close the tornado got to the plant. This tornado basically wiped out the town of La Plata as a strong F4 tornado. I believe F4 and F5 tornados (the strongest) account for less than 1 percent of all tornados in the US in any given year.