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Mount Baldy Wilderness |
Site Name
IMPROVE:
BALD1
Region
Colorado
Plateau
Terrain
Terrain is shown in the 2 km terrain
map and the 20 km terrain
map.
The Mount Baldy Wilderness Area is within the Fort Apache Indian Reservation
in east-central Arizona. It comprises the northeast slopes and drainages of
Baldy Peak, an extinct volcano with peak elevation 3,477 ft (11,403 ft), and
includes the headwaters of the West and East Forks of the Little Colorado
River. Mount Baldy is the highest peak in a large region of eastern
Arizona/western New Mexico. Most of the forest covering the mountain is
mixed conifers with ponderosa pine in the lower elevations and fir and
spruce higher up.
The IMPROVE monitoring site representing the Mount Baldy Wilderness Area is
BALD1, located outside of the Wilderness Boundary about 10 km to the
northeast, elevation 2,513 m (8,243 ft).
Representativeness
The lowest elevation of the Baldy Mountain Wilderness Area is about 2700 m,
where the West Fork of the Little Colorado exits the Wilderness. The BALD1
IMPROVE site is about 10 km to the northeast at an elevation of 2,513 m, which
is below Wilderness elevations. Measurements at BALD1 are thus most
representative of lower Wilderness elevations. In this terrain, there could
be times when BALD1 is within haze that does not extend vertically as high
as Wilderness locations, which could occur during nighttime surface
inversion conditions for example. BALD1 measurements should be
representative of Wilderness locations when the atmosphere is well-mixed.
Nearby Population/Industrial Centers and Local Sources
Nearby Meteorological Data 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. There are no meteorological network sites within Wilderness
boundaries that collect wind data, although the Baldy SNOTEL site collects
temperature and precipitation data that should be well representative of
Wilderness locations. The nearest RAWS site is the
Greer Arizona RAWS site, with data including
wind data since December 1992. Wind direction may be somewhat steered
locally by the south to north flowing West Fork of the Little Colorado River
valley in this area.
The nearest routinely operated upper air site is the Tucson RAOB site,
which conducts atmospheric soundings twice daily. Sounding data from Tucson
should be representative of regional upper air structure.
Wind Patterns
Wind patterns of the region are characterized by predominantly westerly
winds except during spring and summer.
Phoenix wind roses show the
prevailing westerly to southerly wind direction predominance on an annual
basis. A seasonal shift in wind from a westerly direction to a more
southerly direction, not clearly evident in the Phoenix wind roses that may
be steered locally, typically establishes itself in early July and persists
through mid-September and is associated with the
North American Monsoon. During this period
moisture bearing winds move into the region from the southwest at the
surface, from the Gulf of California, and aloft from the southeast, from the
Gulf of Mexico. Convective instability associated with surface heating of
the moist air, combined with orographic uplift as air is transported towards
higher terrain in the direction of the Colorado Plateau, produces frequent
convective precipitation events often associated with intense rainfall,
lightning, hail, and damaging winds. Strongest thunderstorms are often found
in the mountainous regions such as the Sierra Ancha Wilderness. These
thunderstorms are often accompanied by strong winds and brief periods of
blowing dust prior to the onset of rain.
Locally, in the absence of strong regional pressure gradients, flows will be
dominated by the upslope/downslope winds typical of mountainous areas.
Daytime upslope winds will be from the lower terrain to the north and east
and from the upper waters of the Little Colorado River; nighttime drainage
flow will be toward the lower terrain to the east.
Potential local transport routes into Mount Baldy Wilderness include long
distance transport via upward mixing from more distant source regions in the
southwest and transport into the region via upper level flow. Possible
source regions include the Phoenix/Mesa urban area 200 km to the
west-southwest.
Inversions/Trapping
The southwestern U.S. region that is subject to frequent stagnation events
has its eastern edge near the Mount Baldy Wilderness. In this part of
Arizona long-term data indicate an average of at least nearly stagnation
episode per month from May to October, where an air stagnation episode is
defined as stagnation conditions that persist for 4 days or longer (Wang and Angell, 1999). During this
period, pressure and temperature gradients in the region are weakest, and
wind circulations weakest. Subsidence inversions during these conditions may
trap regional haze with buildup over periods of several days.
Drainages on the northeastern flanks of Mount Baldy, which comprise most of
the Wilderness Area, empty towards the upper Little Colorado River valley to
the northeast. Mount Baldy is the highest terrain feature in the east
Arizona – west New Mexico region, it is likely above diurnal surface-based
inversions most of the time, and may be above inversions that contain the
BALD1 monitoring site, and regional haze layers, a significant part of the
time.
Climatological Statistics
Phoenix Normals Means and Extremes are representative of regional climatology at lower elevations. Closer to
the Mount Baldy WA, the
Greer Arizona RAWS site
or the Baldy Snotel site should provide more locally representative data,
although wind direction data from the
Greer Arizona RAWS site may be steered
locally by the upper West Fork of the Little Colorado river valley.
Meteorological Indicators for Local Sources |
Last updated 17 December 2004
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