Understanding the data

Certain terminology may seem difficult to understand for some of the visitors to this site, so here are some brief explanations as to what they mean. If there is something you do not understand, please contact Daventry Weather and I will endeavour to answer your query.

EvapoTranspiration (ET)
Basically, it indicates how good (or bad) a drying day it is. This data is very useful in agriculture and horticulture. If you compare the total ET for the month with the total rain for the month, you can get the deficit in  moisture to know when it is necessary to irrigate. The figure to watch is the final ET reading from the previous day. All record data resets at midnight.

WM2 or w/m2
Simplistically, if the sky is clear (and it's day time) then the data reports as 100% sunny from sunrise to sunset. However, when the Sun rises in the morning and sets at night it is passing through more of the atmosphere than at midday. W/m2 is a measurement of the intensity of sunlight hitting the ground, so the value will be higher at midday when the Sun's intensity is higher because there is less atmosphere in the way. The W/m2 intensity can also be affected by thin high cloud or haze. You might still say it was sunny in these conditions, but less of the Sun's radiation will be reaching you.

What is being measured are the Watts per square metre where the square metre is horizontal, ie, flat on the ground. A square metre ray of energy coming from the Sun will cover approximately one square metre on the Earth's surface when the sun is directly overhead. However, early in the morning and in the evening it hits the ground at an angle and therefore each square metre of earth will be receiving less energy and the reading will be lower.

Dials & Gauges
If you click once anywhere in the Dials & Gauges area, and then hover over certain parts of the displayed data text you will see an explanation which describes how this data is arrived at. Also, if you click on the words like 'Solar', 'Rainfall', Temperature' etc, you can access lots of information in graph form.

Rainfall Information
Please remember that the information shown on the home page is only updated every five minutes. Therefore, it may say it is dry when it has been raining for a few minutes. Dials & Gauges will give a more up to date view of current weather conditions because it is usually only 5 - 8 seconds behind real time. Also, please remember that it may be dry where the weather station is situated, even though you may be having a downpour!

Snow and after effects
When there has been a fall of snow it sometimes takes a while to melt away. When this is happening it can cause inaccurate information to appear on the website as the melting snow 'drips' into the rain catcher. It gives the equipment the sense that it is or has been (a) raining or (b) snowing/sleeting (according to the outside temperature). Please make allowances for these anomalies which are quite beyond mine or the equipment's control. Also, when there has been a sharp frost and water falls into the rain catcher as the temperature rises, it can cause inaccurate information such as "Snowing/Sleet Fall' to appear when there is a clear blue sky. This is caused by the 'dripping' water and the current low temperature, and the workings of the weather station regards these two conditions as being compatible with either snow or sleet.

 Solar Data
Each first of the month the data updates at 09:15, and before then the hours for the month relate to the previous month.

 * Recorded sunshine is just that, recorded by a solar sensor some 12' off the ground. It is not possible to record every single minute of sunshine because the Sun's rays have to be registered by the sensor, and with natural obstacles like Borough Hill and very tall trees blocking the Sun, and the need for the Sun to be high enough for it to be registered by the sensor, it may be up to 30 minutes after sunrise that the sunshine actually starts to be recorded. Furthermore, reports could say 'cloudy' when the sky is clear. For a report to say 'sunny', the software needs a high enough reading to register it as being sunny, but as the Sun starts to go down in a clear blue sky, the reading drops below that required amount, resulting in a 'cloudy' report.

Also, in winter, snow which has settled on the top of the solar sensor, prevents it from accurately recording the correct duration of sunshine.