|
|
|
|
Meteorology
Basin Topics > Air > Meteorology
![[Photo]: Winter sunset over water and mountains. Copyrigh J.T. Ravize - click for more information](/getfile/52560e27-a6d8-4232-9ff2-cdedaf6f5d36/met3.aspx "[Photo]: Winter sunset over water and mountains. Copyrigh J.T. Ravize - click for more information") Lake Tahoe lies in a depression between the crests of the Sierra Nevada and Carson mountain ranges. The bowl shape of the Lake Tahoe Basin has significant implications on air quality. There are two meteorological regimes that affect air quality in the Basin. First, there are thermal inversions that occur when a warm layer of air traps a cold layer of air at the surface of the land and lake. Locally-generated air pollutants are often trapped in the “bowl” by frequent inversions that limit the amount of air mixing, which allows pollutants to accumulate. Inversions most frequently occur during the winter in Tahoe but are common throughout the year. Often, wintertime inversions result in a layer of wood smoke, mostly from residential heating that can be seen over the Lake.
Thermal inversions develop under three conditions in the Lake Tahoe Basin:
- A surface inversion can develop on a clear night, when the earth's surface radiates heat rapidly. Under these conditions, the air directly above the ground can be cooler than the air at higher altitudes.
- An advectional inversion, involves a horizontal inflow of cold air from a source such as a coastal wind.
- Another type of surface inversion can develop at night in valleys, when cold, dense air flows downslope, along the mountains and rests at the bottom of the bowl.
The second most common meteorological event is atmospheric transport of pollutants from the Sacramento Valley and Bay Area. The location of Lake Tahoe, directly to the east of the Sierra Nevada crest, allows the prevailing westerly winds combined with local mountain upslope winds to bring air from the populated regions, west of the Sierra, into the Tahoe Basin. The strength of this pattern depends on the amount of heat, usually strongest in summer, beginning in April and ending in late October.
Average Meteorological Conditions for Lake Tahoe
|
Month
|
Avg. High (*F)
|
Avg. Low (*F)
|
Avg. Precip. (in.)
|
Avg. Snowfall(in.)
|
Avg. Snow Depth (in)
|
|
Jan.
|
38
|
19
|
6.2
|
44
|
21
|
|
Feb.
|
40
|
20
|
5.0
|
37
|
30
|
|
Mar.
|
44
|
23
|
4.2
|
36
|
28
|
|
Apr.
|
51
|
27
|
2.1
|
15
|
14
|
|
May
|
60
|
33
|
1.2
|
4
|
2
|
|
Jun.
|
69
|
39
|
0.7
|
Trace
|
0
|
|
Jul.
|
78
|
44
|
0.3
|
0
|
0
|
|
Aug.
|
77
|
44
|
0.3
|
0
|
0
|
|
Sept.
|
70
|
39
|
0.6
|
Trace
|
0
|
|
Oct.
|
59
|
32
|
1.9
|
3
|
0
|
|
Nov.
|
47
|
26
|
3.9
|
17
|
3
|
|
Dec.
|
40
|
21
|
5.7
|
34
|
11
|
Meteorological ambient data such as temperature, wind speed and direction, relative humidity, and precipitation assist in measuring air quality indicators. Meteorological conditions frequently dictate the amount of air pollution blown into the Lake Tahoe Basin and how much of it is deposited into the land and lake. It is important to measure ambient temperature, wind speed and direction, relative humidity, and precipitation to understand under what conditions air quality samples are collected and to recognize how each variable effects the behavior of individual pollutant types such as, carbon monoxide, ozone, particulate matter, and aerosols. For example, on a windy holiday weekend in the summer, a spike in carbon monoxide can be expected, rather than a surprise, due to the known meteorological conditions and thousands of visitors driving to the Lake and other destinations west of the Basin.
|
|
|
|
|
|
|