Why don't some of the teams impress me and try driving somewhere with black ice, strong crosswinds and blowing snow. If their systems can't drive in negative environmental conditions, they will be largely worthless in many locales.
In my opinion, the fully autonomous vehicles shouldn't need to handle those situations. Leave that up to the human to navigate.
Fully autonomous should be able to handle the NORMAL day-to-day driving responsibilities. If you're going to require those situations that you mentioned, we'll never have fully autonomous vehicles.
NOTE: when I say fully-autonomous, the car will still have a steering wheel and someone sitting in the driver seat. The google car that had no steering wheel would never happen in the "real-world" only tightly controlled environments.
They may be difficult conditions, but people drive in them all the time. Something like 30-40% of the US population drives in snow and wind for months at a time. They're not uncommon. What's the great utility of a car that can only perform its function in ideal circumstances, i.e. on a closed track.
I'd compare it to having a convertible car---it has one lovely feature, that only really proves it worth during elusive weather conditions.
This will make driving in those conditions even more dangerous. If people start relying on self driving cars, their driving skills will deteriorate. If computer can't drive the car safely, rusty driver won't do better job.
If we never see a car that can actually drive itself without human intervention, I will be severely disappointed. All that work and hype just for some driving assistance systems?