Derrylin, Cornahoule DCNN 9576 – A classic example of why private garden sites are not reliable.

54.18913 -7.56126 Met Office CIMO Assessed Class 5 Installed 1/1/98 Temperature readings from 2010

This is my first review of any station in Northern Ireland. I had hoped to find a different regime but unfortunately the same low quality standards seem to be applied there as well. This site displays all the problems I have highlighted in reviews of stations such as Seavington, Cavendish and many others which calls the use of such data into question.

The first problem comes from the lack of any enclosure around the instruments. Anything can come into close proximity at any time which is undocumented and even completely unknown. Here is the Streetview image from the A509 taken in October 2022.

The site does not look especially bad but being alongside a fence next to a field means the adjacent area is probably not under the site owners direct control – anything could come alongside and vegetation levels are not controlled. But that is only a part of the problem when an alternative date image is chosen from July 2021 show this.

The screen can just be made out in front of the large blue and white tents in an area that is under the owners control. Not only are the tents and occupant’s activities likely to interfere with reading accuracy but also the grass height to the nearside of the screen is well above regulations.

I have no wish to demean the work of those responsible for the readings and maintenance of this site, however, there is quite evidently little quality control being enforced. The Met Office uses the data from such sites without having even the remotest surety of their ongoing accuracy. It all appears to be “on trust”.

For example for all anyone could subsequently prove, a barbecue could be lit right alongside the screen quite inadvertently elevating temperatures and nobody would know. A hot day’s readings could suddenly become a “record breaker”. As was shown with the case of Faversham {note: this review will follow soon} no amount of scientific rigour from highly qualified (but independent) professionals could sway the Met office from their belief that their equipment was anything other than totally accurate. Site insecurity issues always seem to be overlooked and as at Floors Castle, inappropriate siting is rarely a concern.

Another unfortunate consideration with such unregulated sites is that of motivated interference. I am not suggesting any specific problems here or elsewhere, but with records carrying such newsworthy coverage, and such small margins as a tenth of a degree being enough , there is always a danger of readings being given a little “assistance”. As I noted in my review of Bournemouth there used to be a great store set by sunshine recorder readings leading to accusations of them being interfered with by rival resorts. Councillors at Gravesend expressed dismay at the closure of their station “Gravesham councillor Mick Wenban (Con) was shocked to learn the news. He said: “It’s a real shame because it always put Gravesend on the map by recording the highest temperatures in the country.”

Derrylin is almost certainly a worthy site run well but there are few guarantees to prove that. The inclusion of its data beyond area forecasting and into use for the historic temperature record as a lowly Class 5 site seems unjustified.

Foot note: I originally drafted this review 21st December 2024, I subsequently noted this:

How does anybody know this figure is genuine?

Source: https://tallbloke.wordpress.com/2024/12/24/derrylin-cornahoule-dcnn-9576-a-classic-example-of-why-private-garden-sites-are-not-reliable/