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FIGURE 3.7 Monthly maximum and minimum temperatures at the Antero Reservoir weather station.

FIGURE 3.6 Mean number of days each month receiving more than 0.25, more than 1.25, and more than 2.54 cm of precipitation at the Antero Reservoir weather station.

FIGURE 3.6 Mean number of days each month receiving more than 0.25, more than 1.25, and more than 2.54 cm of precipitation at the Antero Reservoir weather station.

winter months, December, January, and February (figure 3.5). More than 20% of the annual precipitation falls during August, and more than 50% of the annual total falls during June, July, and August, driven by monsoonal flow from the southwest. Only July and August average more than a few days with measurable precipitation (>0.25 cm/day), and August is the only month with at least one day when more than 1.25 cm of rain falls (figure 3.6). It is rare for more than 2.54 cm of rain to fall during a single day in South Park, such rainfall occurring only approximately once every three years, and then typically in August.

The mean annual temperature for the Antero station is 2°C. Mean January and July temperatures are -16 and 14°C, respectively (figure 3.7). The highest temperature recorded is 28.6°C, in July. In few years does the temperature exceed 26°C.

The coldest measured temperature is -47.8°C, in December. The mean diurnal temperature change is approximately 20°C.

A comparison of South Park's climate with that of boreal sites in Alaska and central Asia, as well as a subalpine forest site in the Colorado Front Range, provides a useful means of understanding the similarity of South Park's climate to that of other mountain areas. Mean January temperatures are lower at the Alaska and Asian sites because they have longer periods of extreme cold weather (table 3.1). South Park does not experience long periods of extreme cold temperatures because polar air masses rarely reach Colorado's interior basins. In addition, the lack of a continuous snow cover allows the ground surface to heat up, preventing the most extreme cold temperatures from developing. Instead cold air masses and cold air drainage onto the floor of South Park combine to produce its extreme cold temperatures. Temperature inversions are dispersed by frequent strong westerly winds. Extreme temperatures rarely persist for more than a few days.

Mean July temperatures are most similar between South Park and Fairbanks, Alaska (table 3.1). Temperatures are warmer at the Asian station and cooler at the Front Range station. Mean annual temperatures are lowest in Fairbanks and warmest in South Park. South Park receives less precipitation than Fairbanks and the Khamar-Daban Mountains of southern Siberia. All sites receive less than 30% of the precipitation that falls at the subalpine site in the Colorado Front Range.

These data indicate that growing-season temperatures are similar between South Park and boreal sites, such as Fairbanks, Alaska, that support continuous conifer forests. The floor of South Park is most likely treeless owing to summer soil drought, much as it is in central Asia, including Mongolia, northern China, and eastern and southern Siberia. Although Fairbanks is in an area of discontinuous permafrost, it is unlikely that permafrost exists in more than a few patches in the highest-elevation cirques and talus slopes surrounding South Park. South Park's semiarid climate is similar to that of both Fairbanks and the Khamar-Daban Mountains.

table 3.1

Weather Data from the Antero Reservoir Station in South Park, Compared with Data from Fairbanks, Alaska, the Colorado Front Range, and the Khamar-Daban Mountains of Southern Siberia

Antero Reservoir

Fairbanks

Front Range"

Khamar- Dabanb

Elevation (m)

2740

50

3109

730

Mean daily temperature (°C)

January

-16

-24

-24

July

14

15

12

18

Mean annual temperature (°C)

2

-3

0

-2

Mean annual precipitation (mm)

258

290

1050

280

aData from the INSTAAR C1 station; Elliott-Fisk (1988). bData from Epova (1965).

aData from the INSTAAR C1 station; Elliott-Fisk (1988). bData from Epova (1965).

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