Oregon gardens get to display superior peony bloom for spring and summer. That is one of several advantages of winter chill. Some plant species appreciate a bit more chill than they can get here. It enhances their performance. However, chill also limits winter bloom. Not many plants want to bloom while the weather is cool, and pollinators are less active.
That is one of several advantages of mild winter weather. It allows flowers that bloom for autumn to bloom a bit later. It allows a few of the flowers that bloom for spring to bloom a bit earlier. There is not much time between the last flowers of autumn and the first flowers of spring. Winter bloom is not as important here as where winters are longer and chillier.
Even if less important here, reliable winter bloom might be a bit more challenging. Some plants that bloom for winter in other climates might be hesitant to bloom for winter locally. After all, they prefer to bloom while the weather is cool. Mild chill might be unsatisfactory. Cool season annuals are unpredictable, but are likely the most reliable for winter bloom.
Of the popular cool season annuals, cyclamen is actually perennial. If not removed at the end of its season, it goes dormant for summer, and regenerates for subsequent winters. It does not bloom as profusely as it originally did, but adds color to mixed small perennials or ground covers that do not bloom for winter. Some types of primrose are also perennial.
A few perennials bloom sporadically and randomly throughout the year, including winter. African daisy and euryops daisy typically do not bloom as much as they do during warm weather, but can. Euryops daisy may actually bloom best during winter. Bird of Paradise flowers mature so slowly that those that begin during autumn might finish through winter.
Witch hazel, daphne, heather, mahonia and winter jasmine bloom for winter, but perhaps not as impressively as for other climates. Some camellia bloom abundantly while others bloom sporadically. Bergenia may bloom later here than for other climates. Forsythia and some spring bulbs, especially daffodil, bloom so early that they seem to bloom for winter.