Portland has a warm-summer Mediterranean climate (Köppen "Csb)" falling just short of a hot-summer Mediterranean climate (Köppen "Csa)" with cool and cloudy winters, and warm and dry summers. This climate is characterized by having overcast, wet, and changing weather conditions in fall, winter, and spring, as Portland lies in the direct path of the stormy westerly flow, and mild and dry summers when the Pacific High reaches in northernmost point in mid summer. Of the three most populated cities within the Pacific Northwest (Seattle, Vancouver, British Columbia and Portland) Portland has the warmest average temperature, the highest number of sunshine hours, and the fewest inches of rainfall and snowfall, although the city still is frequently overcast compared to other US cities at the same latitude. Portland's USDA Plant Hardiness Zone is 9a.