I meant like rest stops, turn-outs, vista-points, etc. how many places are there to pull off the freeway to mess around
Stevie, are you sure about SZ331? SCC site list SZ329 for Prius. I have a set of SZ331 left from 1996 Grand Caravan, last time used in ~'98.. never got around to check if they fit snug on Prius. Edit: US101 could be a good alternative, if conditions are bad. Also Verizon has prepaid 3G plans good luck
I've driven through that pass several times, but only once during a storm. There were tree parts all over the place, and people were driving like they'd never seen rain before, but the weather kinda felt like home, so I didn't have any problems. There are some significant grades and tight corners, at least compared to the rest of I5, but it's a well-travelled and well-maintained road. Be sure to pack along the things you'd normally take for a long trip, dress for the weather, and check the forecast before you head out. Unless you hear of any major problems the day before you leave, or the forecast calls for a large dump of snow, then you should be fine.
For the main problem section, about 20 miles from Henley to the Summit to Ashland, I see a grade of typically 4%, climbing then descending more than 2000 feet. No rest stops here, the last CA stop is just south of Henley, the first OR stop is well past Ashland. The area is sparsely populated. For turnouts and vistas, excluding the Summit itself, I see three historical markers, and a wide spot named Hilt. I'm not remembering much else available. If conditions get dicey, the primary parking lot could well be the freeway itself. But at the moment, I'm seeing a summit forecast of only 1-3 inches daytime Friday, much less overnight and into Saturday. If this holds true, traffic ought to keep this beaten down quite well.
http://www.oregon.gov/ODOT/MCT/docs/SiskiyouPass.pdf advice for truckers remember to use B mode going down hill.
If you get winter tires you will be OK. I'm guessing your winter problems are more with ice and slush rather than snow. I survived last winter (which was cold and snowy) on the Yokohamas just by being sensible (don't try to stop rapidly, don't expect to pull out rapidly, take it easy on corners*, leave good buffers, lift off and press gently if traction control kicks in) but I'm going to get winter tires this year so my wife will be more comfortable driving the Prius instead of the Civic. Most of my winter driving is actually on dry roads so I'm considering Michelin X-Ice which Tire Rack said is a very good on the dry and wet and only lacks a little for ice traction.
I just had a set of X-Ice2s installed on my 15" stock Prius wheels last night. I had very good luck with those tires on a RWD Dakota and my LS430. They do run a bit noisy on the Lexus, though.