Estimate the chance of a snow day.
Closures depend less on absolute snowfall than on snowfall relative to what the area routinely clears — twenty centimetres is trivial in Quebec and paralysing in southern England. Temperature matters separately, because the band just below freezing produces the worst ice on treated surfaces, and wind adds drifting and visibility problems that can close roads with little new snow.
Closure likelihood
Probability = min(55, snowfall / clearance capacity x 55) + temperature band score + wind score, capped at 100
It depends entirely on local capacity. Regions with heavy annual snowfall stay open through amounts that would close an unprepared area many times over.
Because melt and refreeze cycles produce ice, and road salt loses effectiveness as temperature drops. Very cold snow is dry and easier to clear.
Yes. Drifting can block rural roads and reduce visibility to near zero with only a few centimetres of loose snow available to move.