MOLINE, Ill — Many of us have some outdoor thermometer whether it's as basic as an analog display nailed to a tree or post, or a fancy personal weather station. Where you place that thermometer is extremely important to get the most accurate temperature readings. Cindy from Sterling, Illinois, asks, "Is the temperature measured in the sun or the shade?" Let's dig in.
Location matters
Any kind of object in direct sunlight is capable of absorbing some of the sun's energy. In Storm Track 8 University, we talked about albedo; the measure of an object's ability to absorb or reflect energy from the sun. Even objects that have a high albedo can still absorb some of the sun's energy.
That's why it's important to consider where your thermometer is located and pay attention to the type of housing it is in. Most newer outdoor thermometers, especially digital ones, come with a special housing called a radiation shield. Without this shield, the temperature reading is significantly warmer since the sensor is directly exposed to the sun's energy. For example, above are two different readings from the same sensor. The only difference is one has a radiation shield and the other doesn't. Notice the huge difference! A day that we would typically consider to be very comfortable suddenly turns scorching hot!
All official temperature observations that the U.S. National Weather Service uses are from temperature sensors that use some kind of radiation shield. Before digital thermometers became more common, temperature observations were taken from thermometers housed in a weather instrument shelter like the one shown above. The housing still has enough ventilation to get an accurate reading of the temperature while protecting the thermometer from direct sunlight.
So, when measuring temperature, we take the readings in the shade, most often using a radiation shield.
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