On April 9, 2002, just about nine years ago, the Cubs hosted the New York Mets on a Tuesday afternoon where the weather was just about what it's going to be like today (45 degrees at game time, overcast, with the wind blowing in, according to the linked boxscore). The Cubs won 2-0, an unremarkable game in an unremarkable season.
The reason it's worth mentioning is that the paid attendance announced that day was 18,151. That's the last time the Cubs had a paid crowd of under 20,000. Today may be the first time since that date that the Cubs have an announced crowd that small, and with the weather forecast being iffy, it will likely be far fewer than that in the ballpark. The Cubs have to start winning, or attendance the rest of the season is going to continue to spiral downward.
The Cubs' Randy Wells faces the Diamondbacks' Joe Saunders in the season debut for both pitchers. The game starts at 1:20 and will be televised on CSN Chicago.