Tornado Alley (PROG)

[BullNBear52]

Commissioner Edward Davis of the Boston Police Department said two sweeps for bombs had been conducted in the area before the explosions, including one an hour before the attack. However, he said, people were allowed to “come and go and bring items in and out.”

http://thelede.blogs.nytimes.com/2013/04/16/live-updates-in-the-aftermath-of-the-boston-marathon-explosions/

Not the entire city. Just the area around the finish line.