September is generally a very dry month in Seattle (1.3" of rain typically, well below what it is for most months, given nearly 40" of rain per year - remember Seattle gets less rain than NYC), but the pattern late next week looks to be generally cloudy, a little cool, and some chances of light showers, including for Saturday. Nowhere near a washout, as any rain is likely to be quite light. Temps expected to be a few degrees below normal (74/56F is normal for 9/3). Still very possible that gameday is completely dry, as we're still a week out and the chances of showers are low. Wish I could be there...
http://www.wrh.noaa.gov/sew/
http://www.wrh.noaa.gov/sew/