Silent Valley DCNN 9240 – Amazing levels of inaccuracy

54.12690 -6.00192 Met Office CIMO Assessed Class 4 Installed 1/1/1950 Archived Temperature records from 1/3/1977

As is evident from the above image, Silent Valley is an artificial reservoir- the largest in northern Ireland with a surface area of almost 14 square kilometres. It lies 52 km/32 miles to the south south west of Belfast to which it supplies the majority of the city’s fresh water. The reservoir was built between 1923 and 1933 with the weather station credited as being installed in 1950 though there are no digital temperature records prior to 1977. Where this station actually is/was is the matter of some typical Met office confusion, though wherever it is /was is rather academic. Such an obviously unnatural location is not suitable for long term climate reporting purposes – Silent Valley simply never previously existed in its current form 93 years ago.

The Met Office seems to have some difficulty with the elevation readings for the Silent Valley weather station and seem to think it lies at “163m above sea level” as detailed on its current weather map.

This elevation indication is significantly at odds with the CEDA archive which shows the site at 129 metres. I checked this point with “Elevation Finder” (maps below) which showed 126.2 metres amsl and largely in accordance with the archive detail.

This elevation discrepancy may seem trivial ( though a potential difference of 37 metres/121 feet is rather a large amount) but really needs to be explained given the nature of the surrounding topography and vegetation

The above “street view” image from Google Earth shows the Screen at the bottom of 3 tiered levels of embankments to its north. Severely wind shaded from every possible direction, the site is significantly lower than the dam wall to the north. Spinning the imagery through 180° shows the rest of this “natural area” with the 4 km/2.5 miles distant view of open water surrounded by the mountains of Mourne – notably with a surface level elevation of 196 metres.

Where does that Met Office quoted 163 metres elevation come from? Well this screen certainly has done the rounds of locations. Notes in the archives show various different locations and missing readings indicationg no positive evidence of wherever the instrumentation actually was over the period of its somewhat debatable life span. The (rain) gauge will be close by the screen as this is a manually observed site when anyone actually bothers to take observations. In 2024 (the most recent archived data) readings failed to be actually taken 200 times! The overall recent observation record is dismally bad.

2000-03-01

Current

SITE INFORMATION

GAUGE 975692 AT GRID REF 3307E 3216N ELEVATION 135M

And also

2000-03-01

Current

MISSING DATA

GAUGE 975692 FROM 1990 NO DATA AVAILABLE

Silent Valley weather station represents nothing at all natural about the surrounding area and even its lowly CIMO rating of “Class 4 (additional estimated uncertainty added by siting up to 2 °C)” looks unreasonable. Class 5 would be more appropriate as CIMO regulations state such an “expanse of water” should be “significant of the region” which the Silent Valley man made reservoir most certainly is not. Actually taking readings also seems to be an optional exercise.

The most concerning aspect of Silent Valley, however, is the way its (very occasional) readings are being “homogenised” into those of equally dubious other nearby Met Office weather stations. Note that Silent Valley has temperature data from 1977 but is being associated with other sites that mostly post date it. The Met Office Location Specific long Term Averages draws readers to other sites as below.

I reviewed the Killowen weather station in great depth noting how its “climate averages” bore no possible relationship to those other allegedly “well correlated” neighbouring sites. In the case of Silent Valley,that this artificial high elevation site in the Mountains of Mourne is somehow relatable to a modern marina on the coast is a risible notion. I have not yet reviewed Glenanne No 2 (a major site) but the comparisons to Murlough (coastal in the shade), Hillsborough and the ultra frost hollow of Katesbridge are probably the best candidates for most totally uncorrelated possible.

Silent Valley is a weather station of no value whatsoever for historic climate reporting.

Source: https://tallbloke.wordpress.com/2026/04/17/silent-valley-dcnn-9240-amazing-levels-of-inaccuracy/