You're in USDA 8. Zone 7 starts when you enter the mountains. The temperature spreads representing each zone are averages, not extremes. Jasminum x stephanense will be quite hardy for you, don't worry about it. I see it frequently now, but when I first saw it when I worked at Hopkins nursery, near Bothell it was new to me. They had it in a low-lying area with weird, smelly, cheesy soil--probably had endured poor air and soil drainage for years.

Here is a link that might be useful: Washington Zone Map

Thank you.

Is it better off planted in the ground or in a pot? Any suggestions

If using a pot you'd need a pretty big if you want the jasmine to reach full size. And plant in ground generally easier to manage than those in pots, which have to be more diligently watered and fertilized.