“Immediately”

Does the American State Department know something that we don’t?

The U.S. Department of State urges U.S. citizens in Syria to depart immediately while commercial transportation is available. Given the ongoing uncertainty and volatility of the current situation, U.S. citizens who must remain in Syria are advised to limit nonessential travel within the country.

What I’m interested in is this: Why today? Why not last week? The Syrian revolution is six months old, and some are even saying it’s losing momentum. What is it that happened this week that requires all Americans to leave Syria “immediately” ?