Winter road conditions
Road conditions in places that get significant snow are more complex than merely "wet," "dry" and "chance of armadillos." Here are some phrases you'll hear on the radio's travel forecasts:
Terminology and tactics
The road surface may be dry or wet, but is free of any buildup of snow and ice. Most common early in the winter, right behind the snowplough, or after extended sun, when the road surface is warm enough to melt any light buildup.
There is a buildup of slush on the road surface, creating dangerous driving conditions. Slushy roads can easily lead to hydroplaning/aquaplaning. This happens when pavement temperatures are at or near the freezing point and moderate or heavy snow has fallen or drifted onto the road surface. Caution must be exercised when turning or braking -- see the excellent advice under aquaplaning.
Icy or slippery sections
The road surface has icy patches (or wet patches and a temperature near the freezing point). Ice is of course the enemy of traction, which means problems braking and turning, as above. Leave lots of space between vehicles and go slowly.
Winds are picking up light snow which has previously fallen and tracking it across the road surface. This tends to leave some parts of the roadway bare and create dunes (or moguls, if you like) of snow across the road. Traction conditions will vary dramatically, but if the road's been ploughed recently it should be fine for travel.
A light or moderate amount of snow (typically < 8cm) covers the roadway but poses only moderate difficulty. The only serious problem may be finding the lane if you're the first one to venture down it.
Partially snow-covered a.k.a. Center-bare
Pavement is visible in some sections, but other sections are covered by a layer of snow. Some sections may be heavily drifted (big snow dunes) or only the center may be bare. Most disconcertingly, this often means a road with three clear tire tracks - one on each side which may be bare or snow-packed, and a wide one down the middle. When meeting an oncoming vehicle one slows and edges cautiously to the proper side of the road.
Snow-covered or Heavy snow
Like Loose Snow, but typically with more than 8cm of accumulation. Finding the lanes and shoulders can be a real challenge. If possible, wait for the snowplough before proceeding. If not, find a large vehicle who can break trail, and follow at a safe (long) distance.
Traffic has beaten the snow down into a hard cake that covers the road. This can be drivable, but can turn as slippery as ice without warning if it starts to crack into small chunks. Markings on the road (lanes, pass/don't pass) will be completely obscured.
Road conditions are so heinous as to prevent travel, or accidents have blocked the way. Closed roads are not a challenge to machismo or the capabilities of your SUV, they are impassable. Stay where you are and wait for conditions to improve.
In addition to the current road conditions, visibility must be considered. Bare road conditions are no help in a whiteout. The forecast is important as well - it may be bare now, but if a heavy squall is coming you might want to travel some other time.