forecast for sunday's much-anticipated marine corps marathon. john gonzalez is at the convention center with what is happening today to get the runners ready. john: the u.s. marine corps health and fitness expo is underway this afternoon at the d.c. convention center, and this, of course, is the preevent for the big event on sunday morning, the 40th marine corps marathon. ruby red shirts will be given out here for the runners -- ruby red for the 40th anniversary, and there is a lot going on. this is mark goldman. marx, tell me about the expert we have a lot going on. the registration is back here for 30,000 runners. mark: it is the marine corps marathon health and fitness expo. over 100,000 people from all 50 states and 59 countries arriving in the nation's capital in arlington virginia and the first stop is the health and fitness expo. every runner checks in here, get their participant bib, the ruby red. john: 26.2 miles.