Weather data is scientific data and, if you want to get the most out of your new weather station then following some of the basic guidelines set out below will help you to enjoy your new system and ensure accuracy.
Several simple things can be done to make your observations comparable to those made elsewhere or of use to others should you choose to share your data through online clubs or forums.
Accurate weather data can be achieved if the various weather sensors are sited and installed with care. It is not always possible to follow installation guidelines to the letter but simply mounting the sensors of a new weather station in the most convenient location will lead to errors in the data. Individual sensor locations need to be chosen with due scientific consideration for best results.
The standard height for measuring air temperature is at 1250mm above ground level. A fixed height is specified as vertical temperature gradients can be intense. The thermometer or temperature probe should be surrounded by as much free air as possible. Ground level or soil temperatures can be measured with additional probes or thermometers.
The instrument should be protected from direct sunlight and rainfall which is traditionally achieved by placing the thermometer or sensor inside a white louvered Stevenson Screen. These traditional screens are available online at Metcheck. A screen should be positioned over grass away from buildings or patios which absorb and radiate the suns energy.
The same can be said when mounting a Davis Vantage Pro2 which utilises a modern plastic louvered shield mounted underneath the rain bucket. When using a mini wall mounted Stevenson screen or a standard plastic housing provided with complete TechnoLine weather stations, a north facing wall is preferable. A reduction in radiated solar energy from the wall can be achieved by using a wall mounting bracket to allow for the flow of air.
In general the roof is not considered a suitable position for temperature sensors due to the height above ground and solid surface materials. In general if a roof location is all you have or you are using an all in one sensor suite such as the Davis Vantage Vue, use it, but bear in mind the limitations.
Nowadays in most electronic weather stations the humidity sensor is built in alongside the temperature sensor and does not have its own independent siting criteria. Where a separate sensor or manual hygrometer is used, follow the same guidelines as for temperature sensor siting.
According to WeatherFAQs.org.uk: "Rainfall amounts are quoted as a depth of water that would result in any one location on a flat surface after a fall of rain, if there were no run-off, evaporation or percolation. The depth measured in a gauge is assumed to be representative over an area around the gauge, so it is necessary to eliminate as far as possible any local sources of error."
There are many sources of error in rainfall assessment and by far the greatest; which can be easily minimised, is down to inadequate exposure. The 'ideal' location for your rain gauge is in an open area, e.g. a lawn, where nearby objects such as buildings, walls, trees and fences won't deflect wind-blown rain into the gauge or cause air turbulence and consequent non-uniform deposition of rain droplets.
The standard recommendation is that the rain gauge be at a distance corresponding to two to four times the height of any nearby obstruction. i.e. tree height = 10ft, closest rain gauge placement = 20ft. Rain gauges should be positioned in a flat area.
If using a Davis Vantage Pro2 or other electronic rain gauge the rain monitor will utilise a tipping mechanism which must be installed on the horizontal using a spirit level. For Davis Vantage Pro2 stations the rain gauge rim will automatically be at 1400mm height if the temperature sensor is mounted at the official recording height of 1250mm.
It is important to remember that you are measuring rainfall that is of significance to you, the user. In extreme rainfall events any measurements are better than none; even an 'official' gauge under extreme conditions has difficulty in capturing a 'true' measure of the event.
Wind Speed & Direction Sensors
Wind speed and direction in the first 30 metres of the atmosphere are dramatically affected by any physical obstructions and uneven ground. This means readings can vary rapidly with height. The standard guideline for professional monitoring is for wind speed and direction over a level surface to be measured at a height of 10m above ground level.
It is very difficult to find a good location for an anemometer and therefore the recommendation is simply to place it as high as possible. This could be several meters above the highest point of your roof to avoid potentially turbulent air below.
This mounting position will allow you to monitor the conditions for your site. The sensor readings will be valuable as part of your continuing weather record; but due to the significant factors that can affect wind speed and direction it is not appropriate to use the data for comparisons with official records.
Barometric pressure is generally measured by a sensor inside your weather station console and not by an external sensor. As such there are no specific requirements about siting the pressure sensor, other than to be aware that its accuracy is only specified over a limited temperature range.
Pressure reduces as height above sea level increase and as such we suggest you check your site specific altitude to correctly set up your weather station console.
Read our complete range of installation guides to discover more tips: