Capital Weather Gang NatCast has 'It doesn't look like a washout by any means, but there could be noticeable rain drops at times. Temperatures are quite comfortable though' with temperatures in the low/mid 70's throughout and 50% chance of rain. Yahoo! Weather only sees 30% chance of rain, with an isolated thunderstorm.
[oh well it's an afternoon match so rain delays are a bit easier to take]
Don't forget: if you're Metro-ing in today, you might want to budget a bit more time getting in, both because of the track-work and because of the Caps playoff match (face-off 12.30).