Seattle's Climatic Composition

Seattle Washington

    Seattle is situated on a small isthmus boarded on the west by the Puget Sound (an extension of the Pacific Ocean) and to the east by Lake Washington. The city falls at latitude 47" 37' and North longitude 122" 19' West, making Seattle a more northern city than Toronto. The specific geography of the city proper is interesting in that, less than 60% of the city limit is covered by land. With 217 square miles of land and 150 square miles of water, its hard not to argue that Seattle is a maritime city. (The City of Seattle)

Image courtesy of The City of Seattle

http://www.seattle.gov/html/visitor/location.htm

    The topography of Seattle's surrounding area creates a temperate climatic composition. Beyond the western edge of the Puget Sound lies the Olympic Mountain Range on the Olympic Peninsula, which act as a natural barrier for Seattle from the majority of oceanic or coastal weather conditions moving eastward. To the east of Seattle lies the Cascade Range running in a north to south orientation across the entire state. The Cascade Range also acts as a natural geographical buffer. These two massive geologic components help insulate Seattle from the most extreme weather fluctuations. Below is a topographic map of Washington showing the Olympic and Cascade Ranges in relation to the Puget Sound.

Image courtesy of Intermountain AmeriCorps

http://www.intermountainac.com/Location_Information.htm

    Due to the nature of Seattle's surrounding topography, its climate is usually described as oceanic or temperate marine. Its seasonal climate is composed of mild, wet winters and warm, dry summers. For the purpose of observing Seattle's climatic composition I choose a weather station located a few miles south of the city. My station is located at the SeaTac airport and holds weather data records since the mid 1940's. 

    

   The graphs below exemplify the temperate nature of Seattle. The first graph draws distinction to average temperatures according to months of the year. July and August are the warmest with average highs in the mid 70's. The second graph depicts the average precipitation experienced in Seattle according to months of the year. November, December and January are the wettest months as well as the coldest, often resulting in light snow.

Image courtesy of The Weather Channel

http://www.weather.com/weather/wxclimatology/monthly/graph/USWA0395

Image courtesy of The Weather Channel

http://www.weather.com/weather/wxclimatology/monthly/graph/USWA0395

Seattle’s Bowen Ratio

    The Bowen Ratio is a complex formula used to evaluate the energy fluxes of specific geographic regions. By dividing the amount of sensible heat (difference in temperature without evapotranspiration) by the amount of latent heat (the energy required during a change of state, without a change in temperature) we can derive a specific energy profile and the evolution of energy transfer. According to typical Bowen Ratios, moist regions have low ratios, and arid regions have high ratios. Due to the seaport positioning of Seattle, I would suspect the ratio to be about .3. However, due to the nature that Urban Heat Islands have on energy balances, I would rate Seattle somewhere between .4 and .5 due to infrastructure (e.g. buildings or pavement) and vegetation within the city proper. (Dr. Chambers, Geography Department, University of Colorado Denver)