Tiree DCNN6007 – The unreliability of Met Office raw data.

56.499996 -6.880718 Met Office CIMO Assessed Class 4 Installed 1/1/1926 According to Met Office records…...BUT?

Tiree is the most westerly island of the Inner Hebrides with an area of just over 30 square miles and a population of approximately 700. The island is known for being relatively dry for the area with average annual precipitation of 1275mm / 50 inches which equates to under half of, for example, the English Lake District. Although subject to regular Atlantic gales it is deemed better sheltered than other isles and is one of the sunniest of all Scottish islands. Tiree is also noted as a “Historic Station” by the Met Office and this is where things get very dubious.

Checking as usual the operational dates for Tiree weather station, I initially referred to the CEDA file which looks like this (my highlighting)

The quoted start date of 1926 was interesting as the headline image includes the taxiway of Tiree Airport , (formerly RAF Tiree) which, with a main runway of almost 5,000 feet, is comparable to London City Airport and potentially capable of Trans-Atlantic narrow body passenger jet flights. History indicated the airport did not exist in 1926 and was indeed not opened until 1943.

Did this demonstrate an incredible prescience on the part of the Met Office in knowing exactly where the airport would be located 17 years in advance or was the weather station located elsewhere? Clicking on the “View data” link brings up the observational precis of monthly averages under this header below.

Tiree
Location: 99800E 744800N, Lat 56.500 Lon -6.880, 12 metres amsl
Estimated data is marked with a * after the value.
Missing data (more than 2 days missing in month) is marked by —.
Sunshine data taken from an automatic Kipp & Zonen sensor marked with a #, otherwise sunshine data taken from a Campbell Stokes recorder.
yyyy mm tmax tmin af rain sun
degC degC days mm hours

YES the Met Office is showing coordinates that lead to the current airport site though somewhat oddly the actual temperature readings do not start until 1930. Any researcher or student at this point would simply have to accept the “official” record, after all there is no reason to doubt it. Tiree weather station must have always been in its current location – the Met Office data “proves” it, doesn’t it?

A personal view of mine is that most modern day students involved in any form of climate science do not question the data offered to them. To most this site would be known simply as Tiree with no aviation reference at all and, in reality, is likely just a “number stream” of observations that is not relatable to in any tangible way. Graphs will be shown or constructed depicting changes over time from what are just “data”. Real world details seem completely irrelevant when sitting behind a computer screen constructing or viewing reified averages..

So what is the real provenance of this site? Well this is also similar to the issues I raised at Camborne – local historians seem to reiterate what somebody else claims and incorrect information circulates around the internet system producing a form of inadvertent misinformation. In the case of Camborne the site was claimed to be of very long term provenance when it was not – in Tiree’s case its history is greatly underestimated. From this “Facebook” account;

“The Tiree weather station sent its first report in 1926, after the headmaster at Cornaig School started recording rainfall as a hobby. This caught the attention of the Met Office, which was looking for a steady flow of reliable weather measurements from the Hebrides. At first, the instruments were placed in a fenced-off corner of the school playground and the barometer sat on the headmaster’s staircase. The anemometer (which needs to be mounted 10 m. or 33 ft. above the ground) was positioned away from the school buildings above a small hut on the machair. When the new Cornaigmore School was built in 1936, with its electricity and flushing toilets, the equipment had to find a new home, and an enclosure was built around the anemometer hut. The shuttered concrete perimeter wall and hut are there to this day.

In 1942, the equipment was moved again – this time by the RAF, who had taken over the running of the station – to The Camp in Crossapol.

To maintain consistency in the readings, the anemometer was left in Cornaig to be read by the headmaster. In 1946, the RAF weather station was handed back to the Met Office, and re-sited beside an office in the wartime control tower (now demolished, but 100m east of the present control tower); the anemometer was re-sited to the airfield in 1956. In 1995, the instruments were moved for the final time to their present position north of the terminal, and Tiree weather station became famously automatic five years later.“

From another report .

“Tiree’s first meteorological station was set up in 1926 in a corner of Cornaig schoolyard, with headmaster Mr. D O MacLean reporting weather observations by telegraph three times a day. In 1935, the instruments were moved to a purpose-built enclosure to the north-west of the school. Taking over the running of the station during te war years, the RAF moved it again, this time to Crossapol, and the 518 Squadron flew twice-daily weather reconnaisance trips 800 miles out into the Atlantic. The new weather station at Tiree airport was built in 1995 and was automated in July 2000.“

I suspect the Met Office did not want it too well publicised that its “Historic Station” data originated from the “corner of a school playground”. This site, in being a corner, would have sheltered the school children from Atlantic winds on at least two sides. There is no doubt that this would have had a completely different climatology to the airport site – the school would have been a sheltered protected site as opposed to the open requirements of an aviation site.

However, the 1926 start date seemed unlikely. The Met Office was originally established in 1854 as the “Meteorological Department of the Board of Trade” with a strong naval/shipping focus for storm warnings and maritime safety. The Scottish Meteorological Society followed in 1855. Tiree would almost certainly have figured in the predominant purpose of “Gale Warnings” for maritime purposes and has long had the Skerrymore Lighthouse off the island’s southernmost tip. A deep check into the “Scottish Red Book” (which seems to record almost everything possible) showed records back to 1883 with the weather station in close proximity to the lighthouse on high land at Hynish. A telegraph station was installed at Scarinish Post Office in 1888 for rapid transmission of observations.

Again, as the map shows below, this site would have a distinctly different climatology to either of its successors being on high ground overlooking the opposite coast and 5 miles away from the claimed “original” school site.

The net result of all this is that the historic station quoted data cannot be trusted as a continuous sequence due to the major initial relocation followed by further more local ones. Additionally the historic record is somewhat truncated from its original provenance with the Victorian very important site being totally discounted presumably due to an “oversight” in archiving from different source material ( i.e the Scottish Meteorological Socitety records being overlooked)

None of this ever seems to deter the Met Office from displaying quite absurd climate averages. Their Location Specific Long Term Averages manages to conjure up comparatives over extraordinarily large distances. It is quite an amazing “homogenisation feat” using discretly different island micro climates and mainland sites up to 62 miles distant. Colonsay ceased observations in observations in 2017 and Barra stopped in 2007 leaving just Islay (former RAF Port Ellen) Airport and Dunstaffnage on the mainland. I am confident John Marlow (who established the historic station at Dunstaffnage) would question the comparability of Tiree and his progeny!

To sum up, Tiree is another typical example (of many) showing the Met Office splicing together ( in an undisclosed manner) datasets from different locations of different climatology and even seemingly able to “forget” their own history despite producing “Historic” station data. My objective to produce a reconstruction of the Great Britain climate excluded islands due to their unrepresentative nature of a wider area – probably fortunate given the very dubious provenance of so many island sites.

Source: https://tallbloke.wordpress.com/2026/07/26/tiree-dcnn6007-the-unreliability-of-met-office-raw-data/