It really depends on what part of the Upper West Side because the neighborhood is massive and takes on a lot of different communities. Closer to the south part of UWS, parking is a nightmare. The further north and west you go, the easier the parking situation is, but it's never ideal. It's possible to find a spot. It just may take an unusually long time. And, I wouldn't recommend leaving your car out overnight. Most people I know that keep cars in the city rent out space in a garage (usually around $500 / month) to make sure their car stays safe. There are a lot of unexpected elements (theft, fights, blizzards, crazy cabs) that can do some massive damage to your vehicle if you leave it on the street.
