PWS - Siting
Background In order to report accurate weather information, you must take care in deciding where to place your weather station. The process of deciding how and where to install your station is called "Siting". Siting is the single most important factor in reporting accurate readings. In fact, siting influences the accuracy of your weather reading much more than the quality of the weather instruments themselves.
Temperature The most common error in installing a weather station is associated with misplacing the thermometer sensor. Meteorologists define temperature as the temperature is the shade with plenty of ventilation. When placing your weather station, make sure:
- the thermometer sensor never receives direct sunlight
- the thermometer receives plenty of ventilation (it is not blocked from the wind)
- if the thermometer is placed above a roof-top, make sure it is at least 5 feet above the roof-top
- if the thermometer is placed above grass, again, it should be at least 5 feed above the grass surface
- the thermometer is at least 50 feet from the nearest paved surface
Suggestion - use a radiation shield for your thermometer. This way, your weather station can be placed in direct sunlight, with the thermometer located inside the radiation shield.
- http://www.ambientweather.com/amwesrpatera.html sells radiation shields. If you purchase from Ambient Weather, use the coupon code "wunderground" to receive a 10% discount.
- some radiation shields have "aspirators" which is a fan that ventilates the thermometer. This ventilation helps a great deal, especially on hot, still days.
- A cheaper solution if you can not use a radiation shield: you can use a sheet of aluminum mounted about 6 inches from the thermometer. This aluminum must shield the sun at all times and have plenty of ventilation.
Humidity Humidity measurements should reflect the humidity of the general atmosphere in your location. Plants and bodies of water influence humidity measurements. As a result:
- make sure your humidity sensor is at least 50 feet from the nearest tree or body of water
Rain Collector You want the rain colleger (or rain gauge) to receive rainfall as if it were in the middle of a large field. Nearby buildings create "shadows". Imagine if there is a building nearby to the west, and it is raining with a west wind. Your rain collector is bound to miss a lot of the falling rain. A good rule of thumb:
- the rain collector (or rain gauge) should be placed with at least 5 feet horizontal clearance to the nearest obstruction
- if a nearby obstruction is just over 5 feet away, that obstruction should be no more than 10 feet tall
'Anemometer Similar to the rain collector, the anemometer should reflect the wind patterns as if the instrument was placed in a large field:
- the standard wind measurement should be taken at 10 meters (33 feet) above the ground. A roof-top works best. Try to place the anemometer as high as is convenient :-)
- try to make the anemometer the highest object around. 7 feet or more above surrounding obstructions is best.
Special Thanks - Thanks to the CWOP and Davis Instruments for documentation on siting weather stations: http://www.davisnet.com/product_documents/weather/app_notes/apnote_30.pdf