Seattle has a temperate climate, classified in the Mediterranean zone by the main climatic classification but some sources put the city in the oceanic zone (Cfb). It has cool, wet winters and mild, relatively dry summers, covering characteristics of both. The climate is sometimes characterized as a “modified Mediterranean” climate because it is cooler and wetter than a “true” Mediterranean climate, but shares the characteristic dry summer (which has a strong influence on the region’s vegetation).
Temperature extremes are moderated by the adjacent Puget Sound, greater Pacific Ocean, and Lake Washington. Thus extreme heat waves are rare in the Seattle area, as are very cold temperatures (below about 15 °F (−9 °C)). The Seattle area is the cloudiest region of the United States, due in part to frequent storms and lows moving in from the adjacent Pacific Ocean. With many more “rain days” than other major American cities, Seattle has a well-earned reputation for frequent rain. In an average year, at least 0.01 inches (0.25 mm) of precipitation falls on 150 days, more than nearly all U.S. cities east of the Rocky Mountains. However, due to the fact that Seattle often has merely a light drizzle falling from the sky for many days, Seattle actually receives significantly less rainfall (or other precipitation) overall than many other U.S. cities like New York City, Miami, or Houston. Seattle is cloudy 201 days out of the year and partly cloudy 93 days.