(Also See Desolation
Wilderness Area)
Site Name
IMPROVE:
BLIS1 (Bliss State Park, Tahoe Regional Planning Agency)
Region
Sierra Nevada Range
Terrain
Terrain is shown in the 2 km terrain
map and
the 20 km terrain
map.
The 105,165 acre Mokelumne Wilderness Area straddles the crest of the
central Sierra Nevada range 25 to 30 km (15 to 20 mi) south of Lake Tahoe.
Watersheds drain to the Mokelumne River on the west slope and the Carson
River on the east slope. The Mokelumne River opens up into the central San
Joaquin Valley about 80 km (50 mi) to the west. The prominent Wilderness
topographic feature is the Mokelumne River Canyon. Elevations range from
about 3900 feet near Salt Springs Reservoir where the Mokelumne River exits
the Wilderness on the south side to 10,380 feet at Round Top on the north
side. Precipitation averages 50 inches annually on the west slope and as
little as 15 inches on the east slope, 80 percent of it in the form of snow.
The IMPROVE site representing Mokelumne and Desolation Wilderness Areas is
BLIS1 (Bliss State Park) located near the western shore of Lake Tahoe at an
elevation of 2,116 m (6,940 ft), about 220 m (720 ft) above the shore of
Lake Tahoe.
Representativeness
The BLIS1 IMPROVE site is close to and about 220 m (720 ft) above the shore
of Lake Tahoe, within the Tahoe Basin. There is no direct link to Mokelumne
Wilderness, which is generally outside of the Tahoe Basin, except via the
headwaters of the Upper Truckee River, separated from the Wilderness by
higher terrain. BLIS1 is likely more susceptible to local and trapped
emissions in the Tahoe basin that do not extend Mokelumne Wilderness
locations. It may be more representative of Mokelumne Wilderness locations
during conditions of uniform regional haze.
Nearby Population/Industrial Centers and Local Sources
The closest source region with emissions that could contribute to haze in
the Desolation Wilderness is the Lake Tahoe basin. The central valley of
California near Sacramento and Stockton, from which emissions could be
transported to the Mokelumne Wilderness, is some 80 km (50 mi) southwest,
linked to the Wilderness by Mokelumne River. The Reno Nevada area is about
the same distance to the northeast but is generally downwind for prevailing
wind directions and in a distant airshed.
Nearby Meteorological Data Stations
Nearby meteorological monitoring network stations with respect to the BLIS1
IMPROVE site are shown in the data network
map and at
the RAWS station US Climate
Archive site. Data from the
South LT/Lake
Tahoe AP California SAO airport site are representative of the Tahoe
basin. The
Meyers California RAWS site may provide data that shows the timing of
drainage flow from slopes surrounding Tahoe Basin.
Upper air data is collected twice daily at the Reno Nevada RAOB site.
Wind and Transport Patterns
Synoptic winds in the region are generally northwesterly (from the
northwest), with an additional component of more southerly winds in the
winter with the weakening of the Pacific High Pressure System. This pattern
is evident in monthly Reno Nevada Wind Roses. Tahoe Basin is somewhat more sheltered, especially on the west side
where the BLIS1 IMPROVE site is located, and wind patterns near the BLIS1
IMPROVE site are likely more influenced by diurnal flows off the western
slopes of the Tahoe Basin. Within Mokelumne Wilderness which is outside of
and south of the Tahoe Basin, diurnal patterns will be channeled by the
upper Mokelumne River and Canyon. There may be some penetration into the
area of San Joaquin Valley emissions via the Mokelumne River that is not
seen at BLIS1 which is more within the Tahoe Basin airshed.
Potential local transport routes into the Mokelumne Wilderness include San
Joaquin Valley emissions transported directly via diurnal upslope/downslope
flow and valley flow in the Mokelumne River valley, mixed upwards with
afternoon mixing and transported via prevailing upper level westerly winds,
or trapped regionally under a persistent subsidence inversion. This
transport condition, from source regions to the west in the California
central valley, occurs mainly in the summer. The Mokelumne Wilderness Area
is probably more influenced by San Joaquin Valley emissions than by
emissions to the east of the Sierra Nevada crest and down the Carson River
which is downwind from the Wilderness for prevailing wind directions, and
has fewer sources of aerosols.
Highest summertime measured concentrations at BLIS1 are associated with
regional forest fire events. In the absence of such regional events there is
likely to be a significant contribution from vehicle traffic in Tahoe basin
to aerosol measurements at BLIS1, perhaps to a greater extent than may occur
within Mokelumne Wilderness boundaries. In the fall and winter there may be
woodsmoke impacts at BLIS1 that are associated with prescribed burns and
residential burning in the Tahoe Basin. Again, these may not affect
Mokelumne Wilderness locations to the same extent.
Inversions/Trapping
The Lake Tahoe Basin, where BLIS1 is located, lies in a depression between
the crests of the Sierra Nevada range and the Carson range to the east. It
is subject to frequent trapping inversions that result from cooling of
surface air over the lake, a common winter condition, and from drainage of
cool air from surrounding slopes into the basin, a common summer condition.
Surface trapping inversions may at times extend upwards to the height of the
BLIS1 IMPROVE site which is about 220 m (720 ft) above lake level.
Frequently but especially in the winter a layer of wood smoke can be seen
over the lake in the morning, which could affect measurements at BLIS1. In
the summer, larger scale subsidence inversions during regional forest fire
events can result in wood smoke 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), just above the Lake Tahoe level of 1,897 m (6,225 ft).
Climatological Statistics
Tahoe
California Climate data are representative of Lake Tahoe and BLIS1.
Other Northern
California Climate Summaries and
Nevada Climate
Summaries are available from the
Western Regional Climate Center.
Keywords