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Glacier Peak Wilderness Area |
Site Name
IMPROVE:
NOCA1 (North Cascades National Park)
CASTNET: NCS415 (North Cascades National Park)
Region
Northern Cascade Range
Terrain
Terrain is shown in the 2 km terrain map and the 20 km terrain map.
The Glacier Peak Wilderness Area consists of 576,865 acres of the northern
Cascade Range between Lake Chelan east of the Cascade crest and the westward
flowing Suiattle River west of the Cascade crest. The dominant topographic
feature is Glacier Peak, a 3,214 m (10,541 ft) high volcanic cone. Other
mountain summits in the Wilderness are 2,500 m (8,200 ft) or lower in
elevation, and most terrain is 2,000 m (6,500 ft) or lower in elevation. The
Wilderness is drained on the west side of the Cascade crest by the Suiattle
and Sauk Rivers, tributaries of the Skagit River that flows to the northern
Puget Sound. East of the Cascade crest, streams flow to Lake Chelan and the
Columbia River basin. Lowest elevations where streams exit the Wilderness on
the west side are around 400 m (1,300 ft), 300 to 400 m higher than Puget
Sound source regions 60 to 80 km (40 to 50 mi) west of western Wilderness
boundaries. Lowest elevations west of the crest are 350 to 400 m (1,200 to
1,300 ft), close to the Lake Chelan elevation of 335 m (1,099 ft).
The IMPROVE site representing Glacier Peak Wilderness is the North Cascades
National Park site, NOCA1, near Ross Lake on the upper reaches of the Skagit
River on the east side of North Cascades National Park that borders Glacier
Peak Wilderness on the north side. The North Cascades
CASTNET site, NCS415, is also
located in the Skagit River valley 34 km (21 mi) downstream from NOCA1, at
an elevation of 109 m (358 ft), 467 m (1,532 ft) lower than the NOCA1
elevation.
Also, see Meteorological Description page for
North Cascades National Park.
Representativeness
The NOCA1 IMPROVE site is at lower elevation of the Skagit River valley near
Ross Lake, 87 m above lake level and about 200 m below the surrounding ridge
tops. It is 30 km north of Glacier Peak Wilderness northern boundary. The
site should still be representative of lower Wilderness Area elevations at
all times. It may at times be contained within surface based valley
inversions that do not extend to higher Wilderness elevations that are
exposed to regional haze above surface inversion heights.
Nearby Population/Industrial Centers
The northern Puget Sound area near the mouth of the Skagit River is ~ 100 km
(60 mi) west of the NOCA1. The city of Seattle is 160 km (100 mi) southwest.
Nearby Meteorological Network Monitoring Sites
Nearby meteorological monitoring network stations with respect to the NOCA1
IMPROVE site are shown in the data network map and at the
RAWS station US Climate Archive
site. The North Cascades NP CASTNET
site, NCS415, is probably the best source for hourly meteorological data,
including wind data, representative of concurrent meteorological conditions
at NOCA1. The nearest upper air site is at Quillayute Washington (UIL), on
the Olympic Peninsula. This and other upper air sites are accessible via the
University of
Wyoming Dept of Atmospheric Science web page.
Wind Patterns
Synoptic winds in the region are generally westerly, with more northwesterly
flow during the summer when the Pacific High is off the coast of
northwestern U.S., and more westerly flow during the winter when the Pacific
High has retreated southward. This pattern can be seen in monthly Seattle
Washington wind roses (link to Seattle wind roses archived) although these
surface wind patterns may differ somewhat from upper level winds because of
terrain effects. During the winter, with high pressure over the Great Basin
and Idaho and low pressure west of the Cascades easterly gradient (synoptic)
flow is common.
The NOCA1 IMPROVE site is within the upper Skagit River channeled flow
regime, with westerly channeled upvalley flow enhanced at times by
prevailing westerly synoptic flow. Correlation with hourly wind direction
data from the CASTNET NCS415 site may reveal low level transport from the
Puget Sound source region. If it occurs, such transport would likely be
indicated by a diurnal pattern to monitored aerosol concentrations.
Inversions/Trapping
Locally, the NOCA1 site is in a lower valley location and may at times be
within valley trapping inversions that do not extend to higher Glacier Peak
Wilderness and North Cascades NP elevations. On a larger scale, inversion
breakup and vertical mixing during periods of weak synoptic forcing could at
times bring urban emissions from Seattle and northern Puget Sound 100 to 160
km to the west into the area. Mixing heights calculated for Salem Oregon (Ferguson
and Rorig, 2003), a maritime location similar to the Seattle and Puget
sound region, show winter heights generally below 300 m (1,000 ft), which
would prevent urban emissions from reaching the NOCA1 site elevation, but
Spring and summer Salem mixing heights frequently reach to 1,500 m or higher
which could allow Puget Sound urban emissions to mix to the NOCA1 elevation.
Resulting transport to NOCA1 could result from concurrent afternoon upvalley
flow or from entrainment of emissions near the mixing height into higher
level air flow, and subsequent transport to the monitoring site. Calculated
Fall Salem mixing heights were typically 300 to 600 m, lower than in the
spring and summer but occasionally high enough to bring valley emissions to
the NOCA1 site elevation.
Regionally, summertime subsidence inversions associated with the
establishment of the semi-permanent Pacific high-pressure system could
result in regional aerosol buildup over periods of days. Subsidence
inversion heights are typically at elevations of 2,000 to 3,000 m (6,000 to
10,000 ft), well above the NOCA1 IMPROVE site. With weak northwesterly
winds, Puget Sound emissions can become trapped against the Cascades and/or
pushed up the Skagit River valley towards the NOCA1 IMPROVE site. Highest
regional aerosol concentrations may occur during summertime stagnation and
subsidence inversion periods in conjunction with western wildland fires.
Climatological Statistics
Seattle
Washington Normals Means and Extremes are representative of low
elevation locations in western Washington source areas upwind of North
Cascades National Park and Glacier Peak Wilderness Area. Other
Washington Climate
Summaries are available from the
Western Regional Climate Center.
Meteorological Indicators
Keywords
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Last updated 13 December 2004
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