So, what is the minimum temperature that we can let them out in?
We can get temps. as low as minus 40....I know they can't go out in that, even my dogs need to be carried...but what is the lowest they can go out in?
We get cold here in Missouri but not that cold. I keep mine up when it is super cold or snowing really hard because that gets in the feather's and can freeze on there and cause them to get very cold due to the freezing of the snow on their feathers. Because they are curly they do not have as much resistance to the weather when super cold like that. They are better off in their pen away from the snow and bad cold temp. They may get mad at you but better mad then frozen or dyeing from the frozen weather. Sebastopol's because of the feathering can get their feathers frozen fast in super cold temps. So my best advice is to keep them in and feed them good and also give greens if you can since they will be in their pen.
Our geese were fine last year. We would open the door every day to give them the option to go out. They almost always chose to go outside along with the ducks. They have little down coats. We left them in when the temps were -10 degrees F or colder they probably would have still gone out unless it was windy. We have brown and white Chinese and one buff. They sit on their feet when it gets really cold. They would probably like it if you shoveled a spot for them although they don't mind tromping through the snow. Leave a little snow for them. They would take snow baths instead of water baths. When the new snow was soft and fluffy they would throw snow on themselves just like they do with water in the summer. It got as cold as -37 last year. The only problem was a little bit of frostbite on the knobs of the Chinese geese. We tried Vaseline but it didn't seem to help much.
Now with Sebastopol's it is different than an African or the other smooth feathered geese. Yes, they have down but because of the curly feathering when it snows and then freezes and their feathers freeze because they are curly, The feathers can not protect Sebastopol's like it would smooth feathered geese in the cold...
I was told only to give bath water if its well over freezing. I have a toulouse & a embden. They did great last winter (we get the same type of snow & cold). They straw works great when you turn them out. Mine loved the powder snow...they would take snow baths. They were funny to watch!
I will give mine bath water to about 20 - 25 for the smooth feathered ones... the Sebbies will not get it when it's below freezing. I'm in Missouri so not nearly as cold as you. My general rule is they can have pasture time IF the weather is ok for me to be out in while bundled up (any colder and I make mad dashes out to check on everyone every couple of hours). But my night pens are houses in dog kennels, so they can get out in their small enclosures whenever they want to . I have had to make paths inside their pens if the snow gets too deep. Extra bedding and hay (not straw in my case) are always available to help keep feet warm.