Attack - Update
It has emerged today that one of the principal informants who inspired last week's Orange Alert was lying. He failed a polygraph test this week. Also, Tom Ridge is playing down the threat (Ridge says warnings intend to build alertness, not alarm). For example, Mr. Ridge observes that "More often than not, unless you are a victim of the explosion itself, you'll get more radiation flying from New York City to Los Angeles in a plane than you will if you are a couple blocks, a couple miles from the initial explosion." The government also believes that there are fewer than 10 al Qaeda operatives in the U. S. with recent ties to the organization, with 20 to 40.
Location of Attacks
Mr. Ridge suggests that Washington and New York would be prime targets because of their symbolic value, but that targets might shift to other cities if Washington and New York appear to be well-defended.
Simultaneity of Attacks
It seems reasonable to suppose that if terrorist attacks occur within the United States, they will all occur at the same time. Once an attack occurs, it will bring everyone to the highest state of alert.
This means that the weather can't be hand-picked in various parts of the country.
Most Likely Modes of Attack Might Be Silent and Hard to Trace
Some facilities that might make attractive targets would be,
What You Can Do to Prepare