If you're planning to visit DC between Feb. & June 2013, here is a link to the Washington Post list of all weekend track closures which might affect your plans or your decision of where to stay.
When stations are closed, buses replace trains, "linking" around the closed stations which may add 15-20 min. to your trip. Check www.wmata.com.
The following is NOT a comprehensive list - just highlights of the closings that will most affect Tourists. For more info. read the article and look at a Metro map.
Feb. 2-3 - BLUE/ORANGE line - Eastern Market station closed.
Feb. 16-18 - GREEN line - Greenbelt Station closed. (This will affect the public bus/metro option from BWI Airport.)
Feb. 23-24 - ORANGE line - West Falls Church & East Falls Church stations closed. (This will affect Bus/metro option from Dulles airport)
March 2-3 - BLUE/YELLOW line - Reagan National airport station closed.
April 20-21 - ORANGE line - (This is a big one for those staying in VA along the Orange Line!) Court House and Clarendon stations are closed.
May 11-12 - ORANGE line - West & East Falls Church stations closed.
May 18-19 - GREEN line - Greenbelt Station closed.
ORANGE line - Virgina Square & Balston stations closed.
May 25-26 - ORANGE line - West Falls Church closed.
June 1-2 RED LINE - Farragut North & Dupont Circle stations closed. (Will affect trips to the zoo.)
June 8-9 - GREEN LINE - U St. and Columbia Heights stations are closed. (Circulator bus is a good option here.)
June 15-16 - RED line - Silver Spring Station closed.
June 22-23 - RED line - Silver Spring Station closed.
June 29-30 - GREEN line - Greenbelt station closed.