Hi Meg- Thanks for writing. First things first...congratulations on training this season. It has been one of the toughest training seasons I've run through. A lot of runners took their training indoors this winter so you won't be alone on Saturday. Although training on a treadmill is different than outdoors, it is still a great way to prepare for a half marathon. You will notice a difference in pace and effort. That is, your pace inside is typically faster at an easier effort than outdoors. This is due to the elements like wind and the terrain (hills). You also propel your body forward outdoors and "keep up" on the treadmill.
It would be best to hold back on your pace in the first 7-8 miles in Saturday's race, especially since this is your first half marathon. Try to match your effort level rather than focusing on speed or pace. Once you hit 8-9 miles, you know you will finish and can up the pace if you want but it is always wise to invest in the second half of the race.
A few years back, I remember reading about Christine Clark, an elite women's marathoner who lived in Alaska and trained on a treadmill in preparation for the 2000 Olympic Marathon Trials (which she won!). She did so because of the nasty weather and she had a young child and no day care options. She was a 2:31 marathoner... It worked for her and it will work for you too.
I have used a combination of outdoor and indoor treadmill runs during winter months to prepare for numerous marathons in my time. Once in an ice storm, I had to run 18 miles on a treadmill. It was either that, or risk a an injury running on the ice. I was preparing to run the Goofy Race and a Half Challenge, and that season most of my runs were on a treadmill because the weather was so nasty. I not only finished Goofy, I finished 10 minutes faster than my predicted race time.
Happy Trails,
Coach Jenny