What is a COOP station?

A site where accurate and complete observations are taken or other services rendered by volunteers or contractors every day of the year. This does not mean that someone has to be monitoring the weather all the time; instruments are provided to monitor temperature and precipitation.

What does a COOP station measure and report?

Observers generally record daily temperature and precipitation. Data is then entered into the WxCoder website or mailed to the local NWS Weather Forecast Office.

Already an observer and need more COOP station forms?

• WS B-91 Record of River and Climatological Observation
• WS B-92 Record of Evaporation and Climatological Observation

How is a COOP station sited?

In order to preserve the integrity of the network, NWS has established standards for equipment, siting, and exposure.

Temperature Sensor Siting

• The sensor should be mounted 5 feet +/- 1 foot above the ground.
• The ground over which the shelter is located should be typical of the surrounding area.
• A level, open clearing is desirable so the thermometers are freely ventilated by air flow.
• Sensors are not to be installed on a steep slope or in a sheltered hollow unless it is typical of the area or unless data from that type of site are desired.
• The sensor should be at least 100 feet from any paved or concrete surface.

Precipitation Gauge Siting

• The exposure of a rain gauge is very important for obtaining accurate measurements.
• Gauges should not be located close to isolated obstructions such as trees and buildings, which may deflect precipitation due to erratic turbulence.
• To avoid wind and resulting turbulence problems, do not locate gauges in wide-open spaces or on elevated sites, such as the tops of buildings.
• The best site for a gauge is one in which it is protected in all directions, such as in an opening in a grove of trees.
• The height of the protection should not exceed twice its distance from the gauge. As a general rule, the windier the gauge location is, the greater the precipitation error will be.

How does the NWS use COOP data?

Many longer-running COOP sites have periods of record up to or even over 100 years. These records are used to compute means and trends, and to examine monthly, seasonal and annual variations in our climate. COOP observations are used to compute a number of drought indices, including the Palmer Drought Index. COOP observations from sites with a long period of record, a low percentage of missing data, and few station moves are included in the U.S. Historical Climatology Network (USHCN, Karl et al., 1990). This is a high-quality moderate sized data set of monthly averaged maximum, minimum, and mean temperature and total monthly precipitation developed to assist in the detection of regional climate change. The USHCN is comprised of over 1000 high-quality stations from the U.S. COOP network within the 48 contiguous United States.

Becoming a COOP Observer

Though NWS Weather Forecast Offices recruit Cooperative Observers, the distribution of Cooperative Weather Stations is a function of need. Needs are defined by NWS WFOs and data users, while considered within the context of constraints of limited federal resources. Generally one station is needed every 25 miles (one per 625 square miles) to define the climate of the United States in areas of homogeneous terrain. Greater densities are allowed in areas with large differences in elevation, urban heat islands, steep land-sea-lake interfaces, etc. Because the network is over 100 years old (established in 1890), many areas already have the necessary stations operating; however, some observers do resign each year.
Becoming a NWS Cooperative observer volunteer requires the following:

• Willingness to allow NWS to place measuring instruments on your property.
• Willingness to allow at least one visit per year from a NWS representative.
• Willingness to record and report daily temperature, precipitation and snowfall data.

If you are selected to become an official NWS Cooperative station, NWS will provide you with the equipment, training and supervision you will need to perform your duties. Depending on the instrumentation, your site will be visited once or twice every 12 months, more if unscheduled maintenance or training updates are required. Observers receive no pay. If you are interested in becoming an NWS Cooperative observer, email Evan LaGuardia (evan.laguardia@noaa.gov).

Other ways to get involved in the weather community of northern Arizona

• CoCoRaHS - Community Collaborative Rain, Hail and Snow Network
• CWOP - Citizen Weather Observer Program
• Send weather reports to NWS Flagstaff - iNWS
• Interacting with us on Facebook and Twitter

Human measurements (snowfall), standardized manual equipment (rainfall) and automated gauges (temperature and sometimes precipitation) are part of the equipment used by the COOP program. Learn more about these below.

Human-involved COOP Measurements

Rain/Snow Gauge (photos 1 and 2)

The instrument used for recording precipitation is the 8-inch Standard Rain Gauge (SRG); consisting of an outer/overflow can, inner tube, funnel, precipitation stick and tripod support.
The funnel guides rain into the inner tube. In order to provide rainfall measurements to the hundredths of an inch, the measuring tube has a cross sectional area that is one-tenth the cross-section of the funnel. Therefore, when 1 inch of rain falls into the funnel, it fills the measuring tube to a depth of 10 inches. Accordingly, the scale of the measuring stick used with the SRG is graduated to hundredths of an inch.

Snowfall and Snow Depth (photos 3 and 4)

The SRG becomes a snow gauge in the winter. The measuring tube and funnel are removed, allowing wintry precipitation to fall directly into the overflow can. At the time of observation, if there is snow in the overflow can, the COOP site will bring the snow gauge indoors, melting the snow with a pre-measured amount of hot water from the inner-tube, then pour both the melted snow and hot water back into the inner-tube, subtracting the amount of hot water added to get the true amount of water for the melted snow. Using the precipitation stick, the COOP site can then get the liquid measure of the wintry precipitation that fell.
At the time of observation, COOP sites will also measure any snow that fell during the observation period. Using a snow stick they measure snowfall to the nearest tenth of an inch. They also will report any snow remaining on the ground (snow depth) to the nearest whole inch. Snow depth is the accumulated snow from previous snow storms.
Refresh yourself on measuring snowfall and depth here

Temperature (photos 5 and 6)

Many observers record temperature readings: the 24-hour high and low temperatures and the temperature at observation. COOP sites report temperature to the nearest whole degree Fahrenheit. Most COOP sites are equipped with an electronic Maximum/Minimum Temperature System (MMTS) which electronically measures and memorizes the daily maximum and minimum temperatures.

Fischer Porter Automated Gauges

Precipitation

There are eleven Fischer Porter automated precipitation gauges across northern Arizona that are maintained by NWS Flagstaff. These sites measure precipitation at hourly increments. The data is manually downloaded every month with routine service being performed every six months. See the map on the Overview and Station Map tab to view where these sites are located!

Informative Resources

• National NWS COOP Website
• WxCoder Training Guide
• Northern Arizona Climate Data for Select Sites
• Western Regional Climate Center
• National Centers for Environmental Information
• Nimbus MaxT and MinT Instructions
• Nimbus Instructions
• Snowfall Measurement Guidelines, Method 1 and Method 2
• WS B-91 Record of River and Climatological Observation
• WS B-92 Record of Evaporation and Climatological Observation

Measuring Rainfall and Snowfall

Measure Light to Moderate Precipitation

Measure Heavy Precipitation

Understanding Rain Gauges

Measuring Snow

Regional Temperature and Precipitation Information for Northern Arizona

The collected data is invaluable in the NWS' ability to disseminate daily maximum and minimum temperatures, 24-hr precipitation, snowfall and snow depth to partners and customers of our Office. See below for COOP data at work across northern Arizona! Historical hourly precipitation data from COOP stations can be found here. Climate normals from COOP sites are available here.

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