Hey, I have no answer re the treadmill as I don't use one but I say run in the rain. It's great fun i'm up to wk 4 of the C25K and the runs i've done in the rain have been my best

Good luck with your 5k

(1) Run with the treadmill at about a 1% incline. This is the equivalent of running outside on a flat surface - compensates for the lack of wind resistance on the treadmill.

(2) If your race will have hills, include some similar hills in your treadmill training (adjust your uphill speed accordingly).

(3) Consider covering up the display - or at least not looking at it - for at least part of your runs. When you run outside, you will not have the electronic display to give you continual feedback on your pace. Learn to judge your pace independently - e. g. by breathing rate, leg turnover speed and fatigue level - which is what you will need to do during the race.

(4) Consider: if you are doing all your training on a treadmill, in a climate controlled environment - what will you do if it is raining on race day? Some outdoor running in the rain is excellent practice for racing in the rain.

(P. S. I live in Los Angeles where it rarely rains - and it is quite easy to schedule runs to avoid bad weather - but you can't control the weather on race day. So I intentionally started to do occasional training runs in the rain. It was definitely worth it when I recently got poured on during a race).