Hmm, I'm definitely far from an expert, but it seems like this weekend would be too close to the marathon to be doing 20M. Maybe increase the shorter runs this week so your total mileage is still high, then begin your taper as per the schedule?

I am going to miss 1 day this week (Thursday, an 8-mile day) because I am traveling. I am thinking I will either increase Wednesday to 8 miles (was 6 miles) and skip Thursday, or try hard to find someplace to run. I'm going to San Diego, so I know there has to be something, but whether I find the time and am comfortable with the route...