Hello and welcome to active.com!  Given that your marathon is in only three weeks it is best not to try and add another long run at this late date.  I know that it's frustrating to miss a workout, but it's just one out of many that I'm sure you have on your schedule.  The benefits of a long run at this point would be primarily psychological and would be far outweighed by the potential risk of not being fully recovered for your race.  Go ahead and start your taper and focus on the few remaining tempo/speed sessions you still have left.

Good luck!

Jay

ps - Which marathon will you be running?

I like to sit in the sauna when I feel a little cold coming in, but not to long just long enough to clean your cold pores. Resting is never overrated when trainging for a marathon. Good luck whith your race.

I guess it would depend on how many 20 milers you have already put in.

Congrats on your Shamrock.  Glad your last long run went well.  Another so soon?  You're going to get good at this!  You'll find that your times will drop even if you don't push it and do any kind of tempo or repetition work.

My 21-milers usually take me about 3.5 hours.  I believe that I'm benefiting from them insofar as they are getting much easier to finish.  18 months ago, I was pretty "destructed" after them.  Now, I get it done, then go about my day pretty much as if I'd taken the day off.

I believe Galloway has over-distance runs in his training program.

Absolutely!  I'm doing the full Maryland Double (Frederick in the spring and Baltimore in the fall).  Dave is thinking about it but he'd better get a move on because it might fill up fairly soon.  I hope I'll see you there!