I think it's usefulness runs out at like -5F or so, but becomes less effective around 15F. This is for sodium chloride. Calcium chloride is much more effective.
Picked up 0.3". Considering that I was expecting nothing and the precip stayed frozen the whole time, 0.3" is great. The grass and sidewalks are white. Temp now down to 33F.
Ensemble prediction system of the ECMWF. The ensembles run with slightly adjusted initialized conditions. The ensemble spread can show uncertainty in the forecast.