Colorado Climate Center
Historic Stations and Factors
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Description of Historic Weather Stations in Colorado
The National Weather Service Cooperative (COOP) Program is the source of the longest climate records in the U.S. The Cooperative program utilized volunteers to take daily temperature and precipitation observations. Early on, the stations used liquid in glass thermometers and an 8 inch standard precipitation gage. The thermometers were placed in a cotton region shelter (CRS) which was painted white and constructed of wooden slats to allow air to freely flow through the shelter. Over the years, automation took the place of the manual equipment. Thermometers were replaces with the Maximum/Minimum Temperature System (MMTS) which utilizes a thermistor in a gill radiation shield. This system is connected to a display where maximum and minimum temperatures are stored by the device and reset once a day by the observer. The 8 inch standard rain gage has been automated by the Fischer-Porter gage. This is a weighing bucket gage that records every 15 minutes. It is important to note that not all stations were converted to the automated systems. Many observers still use the standard gage, but due to environmental problems with mercury thermometers, many stations have discontinued the liquid in glass thermometers and transitioned to the MMTS system.
Factors that Compromise Long-term Weather Records
The long-term weather records of the Cooperative weather observing network are not perfect and data users should be careful to fully understand where the data comes from and understand factors that can compromise these data. Station moves: Many of the stations in the COOP program have been moved at one point or another due to things like observer changing, surrounding environment changing, etc. If a significant move occurs, there is usually a new station number assigned. However, if the move is deemed compatible with the previous location the number will stay the same. It is important to be aware of these minor moves when interpreting data. Observer changes: If the observer changes, the location is also likely to change which can have an impact on the data. Not all observers are exactly the same and some practices may be different than what the previous observer. Time of Observation Change: The time that the observation is taken has a profound affect on daily maximum and minimum temperatures. A morning observation will be reporting the high temperature for the previous day and the overnight low. An evening observation time will report the high temperature of the current day and the previous nights low. Changing from one to the other can create a bias in the average monthly temperature. It is always important to know what the current observation time is so that one can interpret the data correctly. Technology Change: The transition from the manual equipment to automated equipment can have an impact on the data. The 8" standard gage measures to the nearest hundredth of an inch, while the Fischer-Porter gage that replaced many standard gages only records to the nearest tenth of an inch. This loss of resolution can greatly impact the amount of precipitation recorded. The installation of the MMTS system can also impact the long term records, especially until the observer becomes more comfortable with the new technology. Because the MMTS utilizes different technology for sensing temperatures, there is a bias of a 0.1 of a degree or so on the daily maximum/minimum compared to liquid in glass observations.
Contact of Long Term Climate Data
Wendy Ryan, Nolan Doesken

Western Water Assessment at CU-Boulder Colorado Climate TrendsColorado State UniversityClimate Trends HomeColorado Climate CenterCooperative Institute for Research in the Atmosphere Department of Atmospheric Science