Facility Description

The Storm Peak Laboratory is situated on a 70 km long north-south mountain barrier, oriented generally perpendicular to the prevailing westerly winds. SPL is approximately 1150 m above, and to the east of the agricultural Yampa Valley, and the town of Steamboat Springs, Colorado. Located on a peak with limited upwind vegetation or topography to create local turbulence under normal airflow conditions, SPL is ideally situated for in-cloud measurements (Hindman et al., 1994). This exposure also frequently allows clear-air physical and chemical measurements of the free troposphere (at approximately the 700 mb level) uncontaminated by the local boundary layer (Borys et al., 1986).

The climate at the site can be classified as alpine and below treeline, with the dominant tree species being Englemann spruce and aspen. The tundra-like ground cover consists of grasses and flowering plants. Most of the annual precipitation of 125 cm water equivalent falls as snow beginning about 1 November and ending about 1 May. Typical annual snowfalls are in the range of 400 cm to 900 cm with the maximum annual snowfall accumulation recorded since 1979 of 1138 cm. The snowpack on the ground by mid-winter usually averages 250 cm. During summer, precipitation falls primarily from convective storms. Two periods (usually during June and August) of especially moist conditions and convective activity occur each year associated with monsoonal flow from the Gulf of California.

Temperatures, although having a wide annual range because of the mid-latitude location, have less of a range than that found in surrounding valleys. Summer highs at SPL can exceed 25 C with winter lows reaching -25 C with means being milder in both cases. The lowest recorded temperature at SPL was -33 C during January of 1997. When snow covers the region under clear, high pressure conditions, strong inversions form in the valleys, and temperatures at SPL can be 20 C warmer than the surrounding valleys.

During the winter season when storm systems influence Colorado, SPL is usually enveloped by cloud. An extended climatology of the frequency of cloud events is not available. However, based on numerous field sampling programs which have been conducted at SPL, it has been observed that synoptic-scale storms occur at a frequency of 5 - 7 days, and when storms are present SPL typically remains in cloud for periods of 24 - 48 hours. When SPL is in cloud, supercooled liquid water is usually present. The focus of these studies was the relative contributions to water mass flux to the surface of in-cloud occult deposition versus precipitation. During the periods in which precipitation, cloud immersion, or both conditions were observed at SPL, liquid cloud was present 90% of the time during the winter period, and 58% of the time during the summer period. For the summer study, precipitation occurred on 50 of the 133 days, 27 of which had a cloud immersion event as well. During summer, convective and thunderstorm activity dominates the precipitation type. However, during the summer monsoon periods, low cloud bases and drizzle are common, and SPL is frequently immersed in cloud.

The lab building design includes an office-type laboratory room for computer and instrumentation setup with outside air ports and cable access to the roof deck, a cold room for precipitation and cloud rime ice sample handling and ice crystal microphotography, a 150 m2 roof deck area for outside sampling equipment, a full kitchen and two bunk rooms with sleeping space for nine persons.

Electric power is provided via a buried line (110/220VAC). Two telephone lines are available, used as a dedicated voice line and a line shared for computer Internet communications and real-time data transfer. Equipment available at SPL includes a continuously recording meteorological station with dial-up access, two 10-m instrumentation towers, and individual measurement sensors and samplers listed in Table A. Computer,lab and office facilities are listed in Table B. Access to SPL is accomplished by vehicle over mountain roads in summer, and by snowmobile or snowcat when the snow pack blocks road access by car or truck. Ski lifts can be used during the ski season (late November through mid-April).

The Desert Research Institute is an equal opportunity service provider and employer. The Desert Research Institute is a permittee of the Medicine-Bow Routt National Forests.

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