When you’re measuring temperature, give some forethought to where the sensors and thermometers are located.
According to NOAA guidelines (www.nws.noaa.gov/om/coop/standard.htm), surface air temperature measurements for meteorological purposes are taken at 5 feet above the ground. This height is representative of people’s living and working proximities.
Because the goal is to measure the temperature of free-flowing air, it is necessary to ensure that the thermometer or sensor is reading the heat flux to or from the air—and not other sources, like direct sunlight. A sensor mounted on the wall of a building will measure some useless combination of the surrounding air and the building material’s temperatures.
A small, louvered box painted with bright white paint may serve the do-it-yourselfer about as well as commercially available aspirated sun shields. NOAA’s guidelines also call for the sensor to be no closer to an obstruction than four times the height of the obstruction, and to be at least 100 feet from any paved or concrete surface.
In addition to old-fashioned thermometers, electronic sensors are available, some with wireless communication between the outdoor sensor and an indoor display.