Are tubeless mountain bike tire systems appropriate for winter riding in below freezing temperatures? Is there a low temperature limit that I should avoid riding in? Does the cold affect performance of the sealants?
All of my winter rides are tubeless now. I have successfully used tubeless setups with Stan's at -40F. Many other riders in my area have used them extensively and without issue at temperatures well below zero. Stan's happens to be the fluid used by my LBS, but I am sure there are others that work as well.
The hard part is getting the initial seal to work properly on fat tires. If they don't fail on the initial ride, they are just as reliable as in warmer temperatures.
According to this link Stans is good up to -30 F
Special anti-freeze agents allow the sealant to be used in environments as cold as -30° F.
A comment asked about -40 F. Would it seal a puncture? I don't know. I imagine you can go a bit past -30 F and sealing performance would degrade. At some point it would out right freeze and then for sure it would not seal.
According to the MSDS the freezing point is -20 F. Which does not make sense with the -30 F use.
As for appropriate for winter. If you want to ride at low pressure then yes. Your winter riding may differ from your summer riding. Rock gardens may be covered in snow. Swapping out tires on a tubeless is a LOT more more work. If you ride different tires from summer to winter then factor that in.