« Willamette Valley; Eugene, for example, has twice as many foggy days. There are three primary characteristics about Portland that differentiate its climate from the more typical inland maritime valley: 1. The Columbia Gorge allows more continental air to move in from the east. In fall this creates warm and dry “east wind weather"; in winter Portland gets more than its share of transition weather such as freezing rain and “silver thaws." 2. Portland is a “heat island." The cement buildings and roads radiate heat slowly at night. 3. The major part of Portland is in a bowl surrounded by hills which trap air and pollutants, saved only by our eastern chimney—the Columbia Gorge— which draws air in and out of the bowl. Season by Season April—the Transition to Spring April is the transition from winter to spring. The sky breaks up (slowly) like ice on a lake, exposing cracks and patches of blue in the quiet gray quilt. In February and March there are almost five inches of rain a month; in April two and a half inches fall. The nights are finally shorter than the days. May and June—Gray Spring In April about 30 percent of the winds come from the north/northwest. In May and June it is up to about 55 percent, and by July, our warmest month, over 70 percent of the winds come from the north/northwest. June is a deadend month. The continual flow of storms coming over the Pacific since October slows down. The interior, east of the Cascades, has warmed faster, creating a thermal low in the Maritime valley regions which, like clockwork, every late afternoon and evening draws the mostly rainless Pacific air over itself like gray flannel pajamas. July, August and September— Summer From June to July occur some of the most dramatic changes of the year. Through the spring we average a gain of two hours of actual sunny conditions per month (except for June, which is a standstill month) and then July hits and we gain an average of 3V2 hours of actual sunny conditions per day. The rainfall average for July sounds like a Chilean desert report: .39 inches for the month. The ocean temperature is actually highest in August (low 60s). The effect of this is felt in September and October, when we experience “Indian Summer." As the sun gets lower in the horizon, the land cools off, while the Pacific Ocean, a boundless thermos, is relatively warmer and therefore draws air from east to west. By the time the air reaches the Maritime it has warmed up considerably, passing through several mountain ranges and picking up degrees while descending into lower elevations. October—Transition to Winter From September to November the monthly rainfall average increases over four inches. In October the amount of available sunlight decreases dramatically. In September there may be seven hours of sunny conditions per day; whereas in October the average is down to a little over four hours. There is more fog in October (and November) and the winds, as in April, may be strong and come more or less equally from all three primary directions (south/southwest, south/southeast and north/northwest). November, December, January— The Dead of Winter During these months we get half of our annual average rainfall. There are about 15 hours of darkness a day and slightly less than two hours a day of sunny conditions. Over 50 percent of the winds come from the south/southeast, bringing in cold continental air from east of the Cascades. Any snow that falls in these parts is likely to fall now (six out of an average eight inches annually). February and March—False Spring February and March are more alike than February and January. The rainfall average per month diminishes to five inches from 6V2 inches average for the previous three months. Very little snow falls (V2 to 1 inch per month). From February to April the winds take a three-quarter turn, with the dominant direction changing from south/southeast to south/southwest to north/northwest. The gray and drizzle seems to let up for awhile sometime in February and March, but as surely as the rain it returns, and natives size up the remainder of their wood supply to make it through the gray spring. 29
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