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Glacier National Park |
Site Name
IMPROVE: GLAC1
CASTNET: GLR468
Region
Central Rockies
Terrain
Terrain is shown in the 2 km terrain
map and the
20 km terrain map.
Glacier National Park consists of
just over 1 million acres straddling the Continental Divide in northwestern
Montana, bordered by Canada on the north. It is drained on the east side by
the St Mary River and on the west side by MacDonald Creek that merges with
the Middle Fork of the Flathead River near the Park’s western portal.
Terrain is steep mountains and valleys. Elevations range from about 975 m
(3,200 ft) at the western portal to mountain summit elevations along the
Continental Divide in excess of 2,900 m (9,500 ft).
The IMPROVE site representing Glacier National Park is GLAC1, elevation 979
m (3,211 ft), located just below Lake McDonald near the bottom of the pass
that exits the Park at the western portal near the Middle Fork of the
Flathead River. The pass is about 2 km wide. The Glacier National Park
CASTNET site GLR468, with meteorological monitoring, is also located here.
Representativeness
The GLAC1 IMPROVE site should be representative of highest aerosol
concentrations in the National Park, especially on the west side of the
Continental Divide. With hourly meteorological data from the nearby CASTNET
side it may also give good indication of low-level transport of pollutants
into the park. It may be less representative of actual aerosol
concentrations and composition at highest Park elevations, and of upper
level transport into the Park, during periods of strong surface inversions.
Nearby Population/Industrial Centers and Local Sources
This western Montana Wilderness Area is remote from any major source
regions. The nearest sizable community is Kalispell Montana, 45 km southwest
of the GLAC1 monitoring site and linked to the site via the Flathead River
and tributaries. Missoula is 200 km south of the site. Nearby emission
sources may be associated with the timber and mining industries. Highest
concentrations from local sources may occur during regional wildfire events.
Nearby Meteorological Network Monitoring Stations
Nearby meteorological monitoring network stations are shown in the data
network map and at the
US Climate Archive
and RAWS station US Climate
Archive sites. The Glacier
National Park CASTNET site GLR468 is in close proximity to GLAC1 and
should provide the best available representation of surface meteorology
concurrent with aerosol monitoring. The nearest meteorological monitoring
site with long term data representative of regional conditions is probably
the Kalispell NWS station, although wind direction data from Kalispell may
be channeled by the Flathead River valley. Historical data for this and
other first order NWS stations are available via the
EPA Technology Transfer
Network website.
The closest upper air site is Great Falls Montana (TFX), ~250 km southeast.
Data for this and other upper air sites are accessible via the
University of Wyoming Dept
of Atmospheric Science web page.
Wind and Transport Patterns
Regionally, wind patterns and transport flows are dominated by westerly
synoptic flows, with frequent easterly flows in the winter. Monthly
Missoula Montana wind roses
indicate this pattern, with northwesterly flow predominant at this surface
station and a significant east-southeasterly component in the winter. Note
that these surface wind patterns may differ somewhat from upper level winds
because of terrain effects. Locally in the vicinity of GLAC1, surface wind
directions are channeled by the orientation of the pass at the western
National Park portal, as is evident in Glacier National Park Wind Roses based on 1996-2002
meteorological data from the GLR468 CASTNET site. When not strongly affected
by regional pressure gradients, surface winds at the GLAC1 site follow a
diurnal mountain/valley circulation pattern, with nighttime northeasterly
drainage from McDonald Lake and the National Park interior to the northeast.
Inversions/Trapping
The GLAC1 site is in a pass between the McDonald Lake basin in the National
Park to the northeast and the Flathead River North Fork/Middle Fork basin to
the southwest, with bottom elevation near 975 m (3,200 ft). This Flathead
River headwaters basin is enclosed, with a narrow egress to the Flathead
River valley and Kalispell area further south. The GLAC1 site may thus
frequently be within surface radiation inversions that decouple it with
upper level transport winds and higher National Park elevations, especially
in the winter when inversion conditions can persist for days. During this
condition the site may be subject to local sources such as woodstove
emissions. In the summer regional subsidence inversions during periods of
high pressure and stagnation can result in regional aerosol buildup over
periods of days. High regional aerosol concentrations may occur during
summertime stagnation and subsidence inversion periods in conjunction with
western wildland fires.
Climatological Statistics
Kalispell
Montana Normals Means and Extremes should be representative of the GLAC1
site and similar elevations in this part of western Montana. Other
Montana Climate
Summaries are available from the
Western Regional Climate Center.
Meteorological Indicators for Local Sources
Keywords
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