Those ultra fat 2.6 inch tires on the Urbana suggest to me that they might "float" wonderfully on the snow, and Urbana confirmed for me that the tire was designed with the year round, all weather commuter in mind. Urbana is based in Montreal, Quebec, and Montreal this time of year means snow.
I want to test this out, but we don't exactly have an abundance of snow in Santa Cruz. I tried a reasonable analog: Beach Sand. Conditions this last weekend were 70 degrees and sunny at the beach, a perfect opportunity to test these tires.
As you can see, the blue waters of Monterey Bay look very inviting. Furthermore, the tire "floats" over the sand just fine. I didn't photograph myself on the dry, less compact sand away from the water because I was more concerned about keeping in control, but I can still ride and control the bike in the soft sand.
Unfortunately, for my return trip home, I discovered another type of float these tires excel at - the tires are too fat to fit into the tire slot on bus bike racks, so they sit right on top of the slot!
The bus driver won't let me mount the bike like this, but I eventually found a solution to this problem. If I deflate the tires partially down to about 10 PSI (recommended minimum is 20 PSI), I can jam the tires into place. They're wedged in pretty good, so some effort is required to pull them back out at your destination.
At 10 PSI, these balloon tires are still ridable, though you risk pinching the tube on curbs and bumps and the front tire squirms like crazy. You also need noticeably more effort to make the bike go with the tires so squishy.
If you frequently bring your bike on the bus, you might consider swapping out to a skinnier tire. The Nid De Poule tires otherwise perform surprisingly well, with good rolling resistance and superior shock absorption because of their big air volume.
I discovered another cool feature in Santa Cruz last weekend -- a pair of pedestrians crossed against the light directly in front of me, so I squeezed brakes and the rear tire emitted a satisfyingly loud heart stopping screech. The walkers yelped in fear and clutched their chests in response as they jumped back to the sidewalk. I really hate the idea of generating fear like a car, but I have to admit to a certain visceral satisfaction when I saw the look of terror on their faces. I'll repent of that later.
If you want the Nid De Poule, you have to buy the bike from Urbana -- it's not available for sale individually. Steve tells me, though, that Schwalbe's Fat Frank tire might be similar.