Professional Pilot, January 2018
Thick advection fog blankets Vancouver and the Fraser river Cool maritime air flowing over cold surfaces often produces these fogs along the Pacific Northwest coast Climatologically however the Pacific Northwest includes several climate zones Along the coast especially around the Olympic Peninsula and Vancouver Island the climate is a Marine West Coast climate Due to basin wide circulation patterns in the ocean most west coast places in the middle latitudes are influenced by a cold ocean current offshore that helps to suppress summer temperatures A Marine West Coast climate is a temperate oceanic climate abbreviated Cfb by climatologists where the coldest month averages 54 PROFESSIONAL PILOT January 2018 above freezing 0 C 32 F but no month averages above 22 C 72 F and only 4 months are above 10 C 50 F The f in the abbreviation indicates that there is no distinct dry season rather rain and snow is distributed more or less evenly throughout the year Of course there are some distinctive variations in precipitation throughout this region such as the rain shadow occurring to the ENE of Mt Olympus on the Olympic peninsula South of the Olympic Peninsula and inland of Puget Sound the climate switches over to what is most closely a warm summer Mediterranean climate or Csb While little of the area around Seattle and Bellingham could be considered Mediterranean in the classical sense it does share some general temperature and precipitation characteristics with that European region Temperature wise this Csb region is similar to the coastal Cfb but summer average temperatures in areas away from the coast will tend to be a few degrees higher For example as with the Cfb climate the average temperature of the coldest month in a Csb climate is above freezing But whereas the coastal climate is characterized by even rainfall totals throughout the year the Mediterranean climate experiences a winter maximum of precipitation in which the wettest winter month has at least 3 times more precipitation than the driest summer month and that driest summer month receives less than 30 mm 12 in At SEA Seattle WA July sees just 16 mm 063 in of rain while Dec averages 138 mm 543 in Throughout this Csb region the amount of precipitation can vary greatly For example while SEA averages just 864 mm 34 in of precipitation per year ONP Newport OR along the coast experiences nearly 1778 mm 70 in per year Even with such abundant rainfall ONP sees most of its rain in winter with a July average of just 26 mm 102 in compared to 289 mm 1138 in for Dec Home to several large airports Seattle is more prone to fog and low cloud decks than to rain or snow Nearby volcanoes also mean pilots should check for ash advisories
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