The Weatherstation

The data shown on these pages is produced by a Technoline (LaCrosse) WS-2307, which is sited at an altitude of 260m (860ft) above the village of Pontrhydygroes, Ceredigion, approximately 12 miles (20 km) ESE of Aberystwyth. It is updated 24 hours a day.

The server is currently a Lenovo ThinkServer TS140 running Linux Ubuntu 16.04 (Xenial Xerus). This is both the web server, and the computer which is attached to the weather station, processes and graphs the data. The graphing is done at 10 minute intervals. The current data is gathered at 2 minute intervals.

Until September 2010, the weatherstation was a LaCrosse WS-3600. On 27th August, the outdoor thermometer/hygrometer failed, ending over five years of almost continuous records. This was replaced on 12th October 2010 by the present weatherstation, and the records combined. As a result, however, there is no archive for September 2010, and temperature and humidity data are missing between these dates. Rain and wind data however continued to be recorded until 7th September, when the weatherstation was removed for (ultimately unsuccessful) repair.

Accuracy

Although we are relatively sheltered from winds from many directions (though certainly not from the east), I believe the wind speed often under-reads. The wind gauge is as far from shelter as it could be reasonably placed on our land, but is still fairly close to the house (you may see it in the webcam). That gives considerable shielding from winds from the north and north-west. It is about 2 metres above the ground.

The shielding of the outdoor thermometer, as supplied, is insufficient. The effect of direct sun on the sensor can be easily seen in many graphs. On 3rd June 2006, additional shielding was put in place, which largely solved the problem, except possibly in the early mornings in the summer. The thermometer otherwise agrees extremely well with other thermometers I have (typically to within one or two decimal places).

Tests on the rain gauge suggest it is fairly accurate. Its rocker mechanism records every 0.52mm rain, so obviously on warmer days some is likely to be lost to evaporation. There are periods in the record, however, when rain data has been suspect - due to various factors such as leaves in the collection bucket or insects inside the unit. Rain readings must be regarded as suspect, especially in heavy rain.

The official definition of an "absolute drought" is 15 consecutive days with no measurable precipitation (http://www.personal.dundee.ac.uk/~taharley/weathermiscdrought.htm). The word "Drought" is displayed when this occurs, though as this rain gauge measures in 0.52mm increments, this may not strictly be correct. Other words used, such as "Dry", "Very Dry" and "Parched" are my interpretations.

Occasional obvious bad data for all measurements taken by the outside unit is returned by the weather station. When I notice these, I will edit the log files as appropriate.

Disclaimer: I take no responsibility for the accuracy of any data on this web site; any use you make of data from this site is entirely at your own risk!

The Software

The software used to get the data from the weatherstation is Open2300, by Kenneth Lavrsen. The software for the WS-3600 was Open3600, written by Sander Eerkes and Grzegorz Wisniewski (and based on Kenneth Lavrsen's work). The software used to process the data, produce the graphs and create the archives from the data was written by me, using perl, bash and gnuplot. If you wish to try it out for yourself, I'll need to tidy it up; if I ever do, it will of course be free software.

The Webcams

The present "webcam" is an old Nokia N900 phone, which takes a photograph and copies the image to the server. It is facing roughly ESE.

I have not found it easy to find a web cam that will take good photos in daylight. If anyone has any recommendations, please let me know.

All processing of images is done using ImageMagick. I check the average pixel intensity, and the standard deviation. If these are below a threshold value, I do not upload the resulting image to the web site (and the message "Light too poor" will be displayed). The result of this is that the Fuji camera will tend to operate only whilst the sun is above the horizon. In direct sunlight, the image may be washed out, and poor light will be detected. Exact operation times depend on weather conditions, naturally.

Photographs are taken every 2 minutes. Every hour (except when too dark), the last photograph is archived. The previous 20 archived photos are kept and can be viewed using the Prev/Next buttons on the webcam page. The 14:00 photo is kept for a number of additional days.

Sun and moon data

Sun and moon data are calculated using the Perl modules Astro::Coord::ECI::Sun and Astro::Coord::ECI::Moon, available from the CPAN Perl archive (sun, and moon). The data displayed are for the village of Pontrhydygroes, Ceredigion. In the tables, the next event is highlighted in red. For accuracy, see the documentation in the CPAN archives. On a clear evening, light for walking in the open hills is generally adequate up to the time indicated by marine twilight.

Browser compatibility and standards compliancy

These pages all comply with the World Wide Web Consortium (W3C) standards for XHTML 1.0 transitional and CSS. They have been tested, and found to work correctly, in all popular modern desktop browsers. There is an element of responsive design which should help with mobile browsers, but the main table still needs to be worked on in this respect.

The graphs on the year archives pages do not look good; I still have to work on these.

FAQ

Where does the name tywydd.org come from?
Tywydd is Welsh for Weather.
Why do some numbers not seem to add up?
On the current weather page, some data is read every 2 minutes, and some every 10 minutes. You may be noticing that difference. For example, when it starts to rain, you might see the figure 0.5mm recorded for rain in the last hour, whilst the other box tells you it's dry. Check again a few minutes later.
When I click on a graph for this month, why does it give me last month's graph?
For the first day of a new month, the month graphs are not updated. There is no point; you can always check this month so far by looking at the graphs for today. Similarly, for the first hour of the day, the day graphs are not updated.
I don't like the colours you've used!
For the current weather, all the cell colours except for the wind are weather dependent. Check back when the weather's changed, and see if you like it then!
There is no time given for astronomical twilight. Why not?
Pontrhydygroes is sufficiently far north for there to be just over two months in the year (around midsummer) when astronomical twilight lasts throughout the night. The display reads --:--:-- when this happens.
Can I have your programs?
Yes, but unless you're a programmer, you probably won't either understand them or be able to get them to work. Also, they will only work under Linux/UNIX as they are at the moment, and I have no intention of making them work under any other operating system. Drop me an email if you want them.
Are the pages updated 24 hours a day?
Generally yes, though I don't guarantee it. The server is connected to a UPS, which should avoid problems with short power outages.
How accurate is the forecast given on the current weather page?
It really isn't terribly accurate. It is from the weatherstation itself (i.e. not my calculations), is apparently based on pressure trend and nothing else, and could be improved. I might write something to give a little better forecast, but pressure-based forecasts alone are never going to be very accurate.
After checking your site, I decided it would be a good day for <something>. But it wasn't, and as a result, (I got very wet | I got lost in the mountains | something really bad happened).
That's your problem. See my disclaimer above.
Can I link to your site please?
Of course! Please link to http://tywydd.org/ (you don't need the rest of the URL). I'd also appreciate it if you'd drop me an email to say you've linked to me!

Angharad Shaw