When my daughter was in daycare in Calgary when they did fire drills, each room had a set of blankets that the teacher would bring out and cover the kids for the 5 minutes they were outside. When we had them at work we took our coats but that was because they were hanging by our exit door
There she went out most days unless it was below -15. In Mass, she rarely goes out if it is raining or snowing or windy.... We kind of think it is wimpy.
I think the fire drill should be done how it would be done in a fire. If weather is a concern, it should be addresed in your plan. In your drill, they might only be outside for 2 minutes but in the real thing, it could be a long time.
I've lived in FL all my life. I'm a wimp when it comes to the cold. Anything below 55 and my eyes are watering, teeth are chattering, and bones are aching! If it is freezing outside, my students and I are going out with coats in the event of a drill. Teachers are almost always alerted about upcoming drills (at my school) and I would have the students prepared with coats on. In my experience, getting them to line up and get out the door quickly isn't the issue. The issue is once we get on the sidewalk and there is a mass exodus and kids tend to stray. That's the part of the drill that needs practice. Obviously, in a real drill we wouldn't have our coats already on and we'd just have to suffer through the cold until we were taken to a safe (and warm) location.
Can't they teach the kids to grab their coats on the way, and put them on once they're outside? That doesn't take up valuable time if they work out a system for it and practice that. I think there are many solutions. I'm also not sure why they'd have to be outside for 20-30 minutes. I just asked my kids how it works, and they said that they are not allowed to put on coats because they are trying to learn to get outside quickly, but they are not kept outside for more than five minutes.
How long they are outside would be based on how many classroom's are in the school and having to check in with each one of them to make sure everyone is there( if they walk around doing this it's longer, if they have all classroom's with walky-talky's it's easier). I do believe when they do the drills they have to check every station (i don't know the tech term) where it lights up to tell them where a fire is, and they may have several throughout the school (especially if it's been added unto).
In the Northern areas, I do not believe they should go outside without their coats. I remember one time there was a kitchen fire at my school. We were out on the football field for an hour. It wasn't freezing, but it was cold enough to want a jacket. We all had our jackets on. There was a different time where something happened (I forget what it was), but they took us to a near by church and our parents picked us up from there. It was a bit of a walk still. I must have depended on the time of year. I think even in an emergency you have a few seconds to grab a coat. Not too long ago there was a debate saying with people saying 30 or so seconds was time to save someone's life, surely if you practised and kept the coats near the door 30 seconds would be enough time to orderly grab your coat. IME the fire department does not come in just a few seconds. Here the average 911 time is 7 minutes. In really cold temperatures I would not want to be outside in sub zero temps without a coat for 7 minutes.