MADIS ID: EW6514
Station hardware: Davis Vantage Vue Wireless
Camera hardware: TriVision NC-335PW HD 1080p (added late December, 2015)
Datalogger: Davis WeatherLink (USB)
Software: Cumulus 1.9.4
Server: a reliable old Dell desktop running Windows Vista
Status: Active: no issues
Maintenance: Bi-annual sensor cleanup, Semi-annual battery swap
Elevation: 31 ft
Mounting pole height: 9 ft
Surface type: grasses and weeds
Siting: Located at the boundary of a low-lying wetland and landscaped residential land. Nearest obstruction to wind is shrubbery and trees 20 ft to the north. Wind is least obstructed from the NE, E, and SE and most obstructed coming from the N and NNW. Station meets all other guidelines for siting recommended by Davis for accurate air temperature, RH, and rainfall.
Quality control / Accuracy: See my CWOP page for quality control analysis. On my own, I have verified the accuracy of the station data by comparing it to the readings of two Onset Computer Hobo dataloggers and 3 Lascar USB-2 dataloggers. The most significant error appears when the station is in direct sunlight around noon on calm days.
- Air temperature seems to be running as much as +5 degrees over when the station is in direct sunlight on calm days. Looking at forums, it appears to be a common problem with the Vantage Vue without a fan attached because of its relatively small radiation shield. The issue is reduced with a light breeze.
- Wind direction and wind speed records are not perfect (see siting for more on this). As the station is mounted only 9 ft above the ground, error in wind direction caused by turbulence can be expected. Speed may be under actual values especially from the North and Northwest. With increased wind speeds, wind direction is right on the money with nearby stations.
- The Vantage Vue does not have a heated rain gauge and therefore does not accurately measure frozen precipitation.
Other notes: I am very diligent in making sure I collect the most accurate data possible. I chose the Vantage Vue because it offered similar accuracy and resolution to the Davis Vantage Pro 2, but was offered in a smaller, more affordable package. For the money, this unit is an impressive package (see specifications for details). Calibration remains as it was set by the factory for all measurements except for barometric pressure which is modified based on elevation.
- Note on nighttime air temperature: On clear and calm nights, the station has a tendency to record significantly lower temperatures than other nearby stations. There are a few possible explanations to this phenomenon. Clear skies and low winds promote radiational cooling which occurs rather quickly in locations such as this. Soil type, particularly that which is common in pine forests, is known to create cold pockets because it radiates heat well. The topography of the surrounding area may also provide a clue to the cause of lower than average temperatures. After mapping out the area using a digital elevation model, it is clear that the location sits in a depression which could be susceptible to a modest form of cold air pooling (see graphic). Cold air pooling is a phenomenon in which cold air drains into low lying areas such as the siting location of this station during conditions of high radiational cooling. These conditions are met often throughout the year, but are most pronounced on winter nights such as the ones following:
- On January 4, 2014 the station recorded -16.1 F just before sunrise while the nearest stations recorded around -9 F. At -16.1 F, Davis’s stated accuracy for the Vantage Vue is +/-2.5 degrees F. Conditions were clear and calm.
- On February 21, 2015 the station recorded a low of -18.2 F just after sunrise. The temperature was likely lower, but the station failed to communicate until there was sufficient solar power due to a bad battery. An Onset Computer Hobo datalogger which was located about a foot below the station recorded a low air temperature of -22 F! just prior to sunrise. Conditions were also clear and calm.
Some literature on the phenomenon
Video in nor’easter–> backyard_vue.wmv