I have a MY12, which has the same stupid blue light. It seems that most (if not ALL) the new Subaru models have this engine temperature system, which a lot of Forester owners here dislike.
From what I've heard newer vehicles that use very thin, synthetic oil need to be warmed up in order for the oil to get to its optimal functioning temperature. I'm not an engineer, but if the synthetic oils contract more in the cold than good ol' dino than the engine needing to warm up makes sense. Subaru says it's okay to drive while the light is on, just don't drive it 'hard'.
I live in Florida now, but will be moving to the DC metro area in less than a month. During cold weather I plan on letting it warm up a bit before driving, it shouldn't take more than couple of minutes to warm up and it usually takes me that long to get settled in the car and pull out of my complex before I hit a real road anyway.
I'd just keep the pedal off the floor and the revs below 3500, and you should be fine while the light is on.