Site Name
IMPROVE:
OLYM1
CASTNET: OLY241
Region
Southern Pacific Rainforests
Terrain
Terrain is shown in the 2 km terrain map and the 20 km terrain map.
The Olympic National Park comprises
just over 900,000 acres of the Olympic Peninsula in northwestern Washington.
It is divided into two segments: a mountainous core, the Olympic Mountains,
and a separate coastal strip, stretching for 90 km (56 mi) along the Pacific
coast. Ninety-five percent of the Park is designated Wilderness. Elevations
range from sea level along the coast to 2,428 m (7,965 ft) at the crest of
Mt. Olympus near the center of the Peninsula. Annual precipitation is near
400 cm (150 in) in the western valleys and 500 cm (200 in) at the summit of
Mt Olympus. The area sees the greatest precipitation gradient in the world
for temperate latitudes, with as little as 41 cm (16 in) on the northeast
shore of the Peninsula in the rain shadow of the Olympic Mountains.
The IMPROVE site representing the Olympic National Park is OLYM1, located on
an exposed hilltop (Blyn Lookout) near the northeastern extreme of the
Olympic Peninsula at an elevation of 600 m (1,968 ft). There is also a
CASTNET site, OLY421, located near
Port Angeles at an elevation of 125 m (410 ft) 35 km (20 mi) east of OLYM1
and upwind from OLYM1 for prevailing west wind conditions.
Representativeness
OLYM1 is on the northeast shore of the peninsula near Sequim. Sequim is
in the rain shadow of the Olympics, with sea level precipitation less than
20 inches annually. The rain shadow effect may be less severe at the OLYM1
elevation of 600 m. OLYM1 should be representative of eastern National Park
areas most of the time, although at this elevation there may be periods when
it is above inversion height.
Nearby Population/Industrial Centers and Local Sources
Because of the size of the National Park, different areas may be affected by
different sources. For the northeastern National Park area, where the OLYM1
monitoring site is located, nearby industrial and urban emission sources
that most immediately affect the area are in Port Angeles, 35 km (20 mi)
west, emissions from which may include residential woodstove emissions.
Other portions of the eastern National Park area are across Puget Sound from
the Seattle metropolitan area 50 km (30 mi) to the east and downwind for
prevailing west wind conditions. For the western Park area including the
Coastal section, there are no additional large source areas, although there
may be timber and shipping related industries.
Nearby Meteorological Data Stations
Nearby meteorological monitoring network stations are shown in the data
network map and at the
RAWS station US Climate Archive
site. There are several RAWS and COOP sites around the Olympic Peninsula.
The Blue
Mountain Washington RAWS site located about 20 km west of OLYM1 at an
exposed location, elevation 229 m (750 ft) may provide reasonable
representation of meteorological conditions concurrent with aerosol
measurements at OLYM1, although the period of record is short. There is also
a CASTNET site, OLY241, located
near Port Angeles about 40 km west of OLYM1, elevation 125 m (410 ft) with
longer term similarly representative data. The
Cougar Mountain
Washington RAWS site is about 20 km southwest of OLYM1 at an elevation
of 915 m (3,000 ft), also with reasonably representative hourly data. In the
western National Park areas, the
Sitkum
Washington RAWS site at an elevation of 390 m (1,280 ft) will better
represent similar elevations on the upwind side of the Olympics, and the
Quillayute
Airport WCSMO site collects surface data better representative of the
coastal Park section.
Twice daily upper data is also collected at Quillayute and should be
representative of vertical structure in Olympic National Park.
Wind Patterns
Prevailing winds at well-exposed locations near the northwestern U.S. coast
are generally from the north or northwest throughout the year and especially
in the summer months, a consequence of the semi-permanent high pressure that
lies off the Pacific Coast. Southerly and easterly winds can occur during
the winter, when the Pacific High moves southward and weakens. This pattern
is indicated in monthly
Quillayute Washington wind roses for summer months, which show the
prevalence of westerly coastal winds.
Winter Quillayute Washington
wind roses may be more influenced by local diurnal flows as air drains
to the west off the slopes of the Olympic range in the absence of strong
opposing western synoptic flow.
The Olympic Mountains present an unusual near-circular obstruction to
westerly winds, which consequently tend to divide at low levels and flow to
the north and south, converging on the lee side, where the OLYM1 IMPROVE
site is located. At times, channeling and compression of westerly winds the
Strait of Juan de Fuca can result in high speed “Strait Winds”. Rising
motions above the low-level convergence zone produce clouds and
precipitation that may affect eastern portions of Olympic National Park to
some extent. Near the IMPROVE site, resulting westerly flow is from the
direction of Port Angeles 35 km (20 mi) west of the site. High particulate
loading and light scattering during the winter may be partly due to wood
stove and other vegetative burning emissions in areas upwind and surrounding
the monitoring site. In the western National Park area and the Coastal area
there will be a more direct effect from the ocean including periodic sea and
land breezes. These areas are also sheltered and generally upwind from
anthropogenic sources around Puget Sound that have more direct impact on
eastern Park areas.
Potential local transport routes towards the OLYM1 site include transport or
anthropogenic components from the west, the direction of Port Angeles.
Transport from the heavily populated Seattle area on the east side of Puget
Sound may occur during infrequent easterly wind conditions. The area is also
subject to smoke from wildland fires, natural and prescribed, in this
forested region.
Inversions/Trapping
Temperature inversions are relatively common in the greater Puget Sound
area that includes northeastern National Park locations represented by
OLYM1. In wintertime, the common situation is a surface based radiation
inversion that can persist until ventilated by an incursion of marine air
from the Pacific. In the extended summer months, May to October, the common
inversion condition over the eastern Pacific is a subsidence inversion
caused by the persistent sub-tropical high-pressure system. Typical
inversion heights are 300 to 600 m (1,000 to 2,000 ft), and the OLYM1
monitoring site may be near this height much of the time. In western
National Park areas the summertime subsidence inversion, aided by a diurnal
sea/land breeze is likely, more so than the wintertime surface inversion.
Climatological Statistics
Port Angeles
Climate Data should be representative of low-lying elevations near the
northeastern National Park areas, although these do not include wind data.
Representative hourly data for the area from Port Angeles to OLYM1 that
includes hourly wind data are available from the
CASTNET OLY421 (Olympic National
Park) site.
Quillayute Airport Washington Normals Means and Extremes are
representative of lower elevations in the western National Park areas.
Seattle Washington
Seattle Tacoma
Airport Normals Means and Extremes are representative of eastern Puget
Sound locations. These and other
Washington Climate
Summaries are available from the
Western Regional Climate Center.
Keywords