Has little to do with air temp. Cold subsurface road temps. Falling snow falls on untreated roads initially melts then evaporative cooling reduces surface temp and it freezes as more snow falls. Cars compress it to ice. What could be worse is roads treated a tenth of rain falls washing off treatment then heavier snow falls. I see a mess coming up in areas that get initial rain. And yes the temps drop all day which will flash freeze and puddles and eventually drop low enough to negate salt treatment