There are several different types of instrumentation used by Cooperative Weather Observers to keep track of the weather. However, all the instrumentation is standardized, meaning the instruments are identical at all stations across the country. Cooperative Observers typically measure two things, precipitation and temperature. We will discuss the instruments used based on the parameters being sampled.

  • Temperature

photo photophoto 210-4420 Min-Max Thermometer Set

Figure 1 and Figure 2            Figure 3 and Figure 4

Generally, two different types of thermometers are used to measure the temperature. The first, and older method, is using maximum and minimum alcohol thermometers housed in a Cotton Region Shelter (CRS, figure 1). The CRS is made of wood, and is designed to allow proper ventilation to the thermometers housed inside. The thermometers rest at 2m (approx. 6 ft.) above the ground, as specified by the World Meteorological Organization standards. Inside each thermometer is a small "plug" which restricts the flow of alcohol. For the maximum temperature, the "plug" sits at the top of the alcohol, and remains at the highest point until reset (resetting is done by spinning the thermometer). Where the "plug" rests is the daily high temperature. Similarly, in the minimum thermometer, a "plug" will sink to where the low temperature is. Resetting is done by tipping the thermometer upside down.

Newer temperature sensors have been created and distributed in the modernization process of the COOP program. The new sensor is a Maximum/Minimum Temperature Sensor (MMTS). The MMTS is a RTD type thermometer, meaning it uses electrical resistance to record the temperature. The RTD sensor is housed in a "beehive" (figure 2). The "beehive" also rests at the standard 2m level. A cable carrying the signal from the temperature sensor extends into a nearby building, where it is output on a display box (figure 3). Resetting is done with a few simple button pushes.

The accuracy of the alcohol thermometers varies, and is generally within 1 degree F. The accuracy of the MMTS also varies, and is typically within 0.5 degree F.

The maximum and minimum temperatures (figure 4)are then recorded onto a B91 form, and sent in to the local Weather Forecasting Office (WFO) at the end of each month.

  • Precipitation

photo photo

Fig.5 and Fig. 6

Generally, COOP observers who measure precipitation take 24 hour rainfall totals (although special observations may be requested in certain situations). The two main pieces of equipment used for precipitation measurements are the Fisher & Porter Gauge (FPG) and the Standard 8in. Rain Gauge (SRG).

The FPG is essentially a scale that weighs how much water has fallen. Rainwater enters the gauge through an opening at the top (figure 5). It then collects in a container inside the closed cylinder. The container rests on a scale, which records the weight of the water. This measurement is then recorded by a system that punches holes into special graph paper, based on what the weight is. The graph is then sent to the local WFO, which is then sent to the National Climatic Data Center (NCDC) in Asheville, NC.

The Standard Rain Gauge (SRG) is similar to the FPG, with the exception that automatic measurements are not taken. The rainwater collects into a plastic cylinder which is housed inside the larger 8 inch diameter metal cylinder (figure 6). The observer then removes the cylinder and measures the depth of the water with a supplied ruler. The measurements are then recorded and sent to the local WFO. From there, they are sent to NCDC in Asheville, NC.