Slippery when dry

[patchin]

Just got back from Utah. Thank God my son and ex did a great job of looking after our tank. Coming through Nevada we saw several signs before overpasses that read "Icey when dry" or something like that. We were trying to figure that one out. The only thing I could imagine was water vapor going straight to a solid(ice) without turning into water first(sublimation?). But it would have to be pretty darn cold to do that. Any physicists out there? Mike?

 

[jkreefer]

Its for Black ice i think

 

[sfsuphysics]

Not cold, low pressure! Way lower than exists where roads do here on planet Earth. JK most likely has it right, black ice. Basically the ground can be really cold, that the moisture in the air freezes to it making it slippery, thats where the "when dry" part comes in.