Main sensor suite
Davis Vantage Pro 2 wireless weather station
location: Winnipeg, Manitoba, Canada
- located in southwest
portion of city (Charleswood)
station upgraded to Vantage
Pro 2 with fan-aspirated shield - Sep 2015
- main unit mounted
in backyard, anemometer mounted on chimney on roof
Official wind readings are taken from well exposed airport sites at a height of 10 meters (33 feet) Thus, wind readings from my site (about 2/3rd the official height and less ideal exposure) will be less than airport observations, usually by half or more. My wind anemometer is roof mounted on the side of a chimney, about 20 feet up. Even so, wind speeds are greatly influenced by neighbourhood trees and houses which dampens the wind considerably and results in highly variable speeds alternating between light and stronger gusts. Thus, wind readings from my site will be under-reported, especially when trees are in full foliage. Wind readings are better between October and May when surrounding trees are bare. Full tree foliage will lead to lower overall wind readings during the summer months. Note that due to the less than ideal wind exposure at my site, wind chill readings will always be underdone compared to official airport values. As a result, it is not recommended to use my site to monitor wind chill values such as for schoolyard purposes.
The temperature sensor is housed in a 24 hr fan aspirated radiation shield on the unit placed in full sun. Temperatures are generally quite reliable (within 0.5C of official readings).. especially on cloudy and/or windy days. However during sunny, light wind days, my station will usually register readings that are about 1C too high compared with official airport observations. This is most evident from mid morning through early afternoon when the unit gets full solar radiation and there is little ventilation to mix the air surrounding the unit. My backyard has a southern exposure and will warm up considerably in sunny light wind situations.
The humidity sensor is housed with the temperature sensor inside the fan aspirated radiation shield. I have found humidity readings are quite reliable, often within 5-10% of official readings. Most often, humidity readings tend to be a little higher than official airport observations mainly due to less ideal mixing. However, my sensor seems to reach a maximum relative humidity of about 88%, even in dense fog situations. Note that the dew point is calculated directly from the relative humidity reading and air temperature.
Rainfall is the most variable parameter, and depends largely on the prevailing wind direction, and the intensity of rainfall. Generally, I have found that the unit is very comparable to my nearby official weather service rain gauge (Type B standard gauge), often within 0.5 mm of each other. However, I have noted that my VP gauge tends to underestimate rainfall in events with a prevailing north wind, since the unit is somewhat sheltered by trees to the north. Note also that tipping bucket rain gauges tend to underestimate rainfall in high intensity cases. My VP rain gauge is not equipped with a heater.. thus winter precipitation is not recorded. Rain does not generally occur in this climate from November through February. Rainfall season begins April 1st.