Climate in the
Pacific Northwest
The cascade Mountains are a big
part in the seasonal variations in the regions climate because of the
barrier that they create. The barrier is between the
lower-atmosphere
and the maritime climate influences to the west and the continental
climate influence to the west. On the west side of the cascade
Mountains there are low-lying valleys have a maritime climate with
typically abundant winters rains, infrequent snow, dry summers and very
mild temperatures year-round. It is normally above freezing in the
winter this makes it so that when it snows it seldom remains for more
than a few days.
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The climate of the pacific north west region
is
shaped by the interaction of the seasonal varying perisher and wind
pastern. Beginning about mid-October a semi-permanent low
pressure cell, commonly called the Aleutian low intensifies and
migrates southeastward to a location over the Gulf of Alaska. The
winter surface winds blow in a counter clockwise circular pattern
around the Aleutian low. To the south winds blow in a clockwise
circulation around a semi-permeant center of high pressures. Together
these high and low pressures cells typically brings moist, mild,
onshore and westerly flow into the Pacific North West from
October through early spring.
The Pacific North West “Wet-Season”typically
begins
in October, peaks in mid-winter, and ends in the spring; About 75% of
the regions annual precipitation falls in the period October -March.
The results is a strong reduction, from late spring through summer, of
on shore winds and precipitation bearing storms for the Pacific North
West.
Although the west side of the Cascades is
generally
a very wet-region of the Pacific North West, It contains several areas
that receive significally less precipitation than the west-side
average. Washington’s Puget Lowlands, The northwest extreme of the
Olympia Peninsula, The San Juan Island archipelago and Oregon’s
Willamette Valley are relatively dry areas that lie in “Rain Shadows.”
Rain Shadow in these areas are caused by high terrain located to the
west and southwest that shields them from the direct impact of storms
that follow the wet-season’s prevailing storm track.
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The rain-shadow effect is especially strong
for the
region east of the Cascade crest. Most areas east of the Cascade Range
receiving more than 50 cm per year have west-facing slopes and
relatively high elevations. The Cascade Mountains also bear strongly on
the seasonal variations of the region’s climate because they present an
affective barrier between the lower-atmosphere’s maritime climate
influences to the west climate and the continental climate influences
the east.
