They could make the legislation clearer (not to mention more interesting) if they put some pictures and examples in it. Luckily, there's the internet, so bicycling authorities (disclaimer: actual authority not verified) such as myself can easily publish some examples for the public, and courts, to judge things by (disclaimer: actual applicability in a court of law not verified).
We'll start with an easy one:
What about this one, is this rideable or not rideable?
Verdict: not rideable. However, that was a trick question: there's not a cycle path underneath the snow there, it's just a sidewalk.
How about this one? Yes, there's a cycle path in there somewhere.
Verdict: rideable, you wuss.
Ok. What about the next one?
This one is pretty typical in wintery Helsinki: the cycle path is in a hideous condition, and the road adjacent to it has been licked clean. It might be possible to ride this, if you have enormous thighs, and an enduro bike. It would seem pretty stupid to try it on a city bike, such as the one pictured, though.
And yes, 10 metres up the road it seems evident that the cycle path is totally gone:
Verdict: Not rideable. Please proceed to ride on the road.
When confronted by conditions such as these, year in year out, one begins to form the idea that the rideability of a cycle path is relative: it depends on your choice of bicycle, state of mind and general obedience to the letter of the law.
Take a look at the same site a couple of weeks later, for instance:
They've taken the huge bank of snow away, so yes, basically, it is possible to advance on a bicycle on this cycle path. However, they've left a 10 cm cake of bumpy, uneven ice and snow on the cycle path, while the adjacent road remains licked clean. Riding on the road, it's possible to keep up a decent average speed comfortably. Riding on the ice, some parts of the bicycle and your teeth begin to fall off from all the rattling and bouncing. It's slow, uncomfortable and hazardous. The level of maintenance for this cycle path doesn't even begin to address the requirements for fluent bicycling. They've just, narrowly, fulfilled the minimum obligation. The road adjacent remains free of snow. There's very few cars going there. There's only a 40 kph speed limit. Verdict: the cycle path is not rideable for a sane person.
There's not a question of moving to an adjacent road here, because there isn't one. I'm just complaining. If it is below zero, this cycle path is horribly slippery, bumpy and uneven. If it is above zero, this cycle path is horribly slippery, soft and treacherous. Both ways, the weather is fine for bicycling. It's the level of maintenance that sucks. It would be possible to maintain this cycle path so it would be good for bicycling. They just don't do it, for whatever reason.
Here's an example of a cycle path left care of Mother Nature since the latest blizzard (a couple of weeks ago) with the temperature a couple of degrees above zero:
Verdict: rideable (but horrible, profane cursing while riding is allowed). Optimistically thinking, riding a bike in conditions like these improves one's balance a lot.
Then again, there's not only snow, but other kinds of obstacles as well, that can render a cycle path not rideable. Like, for instance, the vehicles of Rakennus Tapsa and his four colleagues, parked directly on the public cycle path, while Tapsa and co. are embiggening the Hartwall Areena: