I think that just because the Muslim holidays will be over, doesn't mean the threat is.
9-11 was not any Muslim or US holiday, it was "just another day", until the attacks made it significant.
Also:
http://www.freerepublic.com/focus/f-news/1068666/posts FBI and DHS Warns of National Rail System Vulnerabilities (to terror attacks, mentions sarin gas)
WASHINGTON, DC: According to reports from law enforcement sources, a FBI and Department of Homeland Security Bulletin warned that there was a continuing terrorist threat against U.S. subways and railways. The bulletin released on Wednesday said that although no specific information pertaining to an attack existed, "such an attack could not be ruled out."
Mentioned in the bulletin was Usama bin Laden's long-term fascination with the 1995 sarin gas attack on the Tokyo subway system.
"An attack on a subway or rail system could cause substantial loss of life, and would have an adverse impact on public confidence, resulting in massive economic loss," the bulletin said, according to a report of it by FoxNews.