National Weather Service United States Department of Commerce

Maximum/Minimum Temperature Sensor

MMTS shelter MMTS readout
Maximum/Minimum Temperature Sensor, MMTS, is an electronic thermometer not too different from the type you buy at the local electronics store. The MMTS is a thermistor housed in a shelter which looks similar to a bee hive. Currently the MMTS requires a cable to connect the sensor with the display. Future plans call for wireless devices which would eliminate many of the problems currently associated with the cabled systems.

Standard Rain Gauge

Standard Rain Gage
The most common is the non-recording gauge called a Standard Rain Gauge, SRG. Typically the SRG is a metal cylinder with a funnel on top and a plastic measuring tube in the middle. The measuring tube can handle up to 2.00 inches of rain before overflowing into the larger outer cylinder. During the winter, the observer removes the funnel and inner tube and allows the snow to collect in the outer tube. The observer then melts the snow and measures it, getting an accurate water equivalent to report.

Fisher & Porter Rain Gauge

Fisher Porter Rain Gage Fisher Porter Rain Gage Tape Punch Mechanism

The most common type of recording precipitation gauge is the Fisher Porter (F&P) gauge, developed by the Belfort instrument Company. The Fisher Porter gauge is designed to work for many years in remote and harsh environments. The F&P gauge weighs the precipitation it collects in a large metal bucket. This bucket sits atop a mechanism which converts the weight of the water into the measuring unit of inches and then, every 15 minutes, punches holes in a paper tape, recording the amount of precipitation. In the winter months the bucket is filled with anti-freeze which allows snow and ice to melt and be accurately measured. The observer removes the tape once a month and sends it to the local NWS Office. After reviewing the data the tape is sent to the National Climatic Data Center for archiving.

Proper Siting

The COOP network has provided climate and weather data for over 100 years. Consistency of the measurements is an attribute of the network, and it has been maintained by rare and/or gradual change, and established standards for exposure, of instruments over the life of the network. 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 [radiation] is located should be typical of the surrounding area. A level, open clearing is desirable so the thermometers are freely ventilated by air flow. Do not install the sensor 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. When possible, the shelter should be no closer than four times the height of any obstruction (tree, fence, building, etc.). 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.

Rooftop Temperature Bias Study