Cassley DCNN 0343 – Foehn (and other) Effects.

58.16818 -4.72721 Met Office assessed CIMO Class 1(disputed) Installed 1/1/1960

Following on from the Met Office’s revelation that all their sites’ records defaulted to CIMO Class 1 and Met Office ranking “Excellent” from my query of the Hastings site, I investigated the strange case of Cassley.

Oldbrew has previously analysed the Foehn Effect, an occasional wind phenomenon that can cause dramatic temperature changes. Clearly this was evident at Cassley

https://tallbloke.wordpress.com/2019/12/30/scottish-highlands-experience-16-8c-december-temperature-record-due-to-the-foehn-effect/

The BBC also highlighted Cassley in its typically exaggerated style given to all weather events

“A record temperature of 16.8C was verified for Cassley in Sutherland. It was recorded at 03:00 GMT on Sunday 29 December. It is the highest on record for 29, 30 or 31 December.”

Searching online to locate the Stevenson Screen at Cassley I fortunately came across an online photograph of the Cassley Hydro Electric power Plant on Loch Shin with the screen to the right of the electricity transmission pole.

Examining the google satellite image indicates the entirety of the power station, its access road, surrounding hard standing and external air cooled transformer (emitting substantial waste heat) are within a 100 metre radius of the screen. Exactly what percentage of that radius is covered is not possible to ascertain this way, if it did not exceed CIMO Class 1 requirements it would be a close issue. However there are other aspects to Class 1 – to clarify here are the details.

The obvious slope to the site evidenced in the above photograph is confirmed by the tightly packed contour spacing on the area Ordnance survey map rising from 100 metres at the station up to 200 metres in the extract below.

Further CIMO Class 1 details the following

Overall my personal view was that, over and above, the Foehn Effect this site was encountering (a condition for this to occur is sloping land) – it could not be regarded as meeting Class 1 rating with multiple failings. Class 3 or more likely Class 4 was appropriate. I therefore queried this via the Met Office manager who had previously responded to me on this subject. The Met Office response was even more enlightening than previous responses.

Rather than answer my questions, a senior Met Office manager, Karl Shepherdson, offered to discuss the subject with me:

“Dear Mr Sanders

Thank you for approaching a couple of my team members recently about CIMO Screen Temperature classifications at a couple of stations. We do get a number of similar enquiries.As their manager I’d like to introduce myself and hopefully assist you with any further enquiries you may have………

……….I’d be very happy for you and I to arrange a telephone or video call conversation, at a mutually agreed time, and I can maybe answer any questions you may have? 

I felt I had made a breakthrough and eagerly responded. I did not want a general “re-education” so replied framing the basic points on which I wanted clarification. The next response stunned me.

Dear Mr Saunders, (editor’s note:yes incorrect spelling)

Thank you for your email last Friday. I can confirm the classification of Cassely Screen Air Temperatures is correct.

It may be worth a read of some of our online resources to give a broader understanding of our wider approach to inspection and quality management at our weather stations, please see here: https://www.metoffice.gov.uk/weather/learn-about/how-forecasts-are-made/observations/observation-site-classification  

In order to ensure any future queries receive our fullest attention, the most appropriate route will be to correspond via enquiries@metoffice.gov.uk  

Best regards,

Karl.”

So no discussion after all plus the instruction not to contact Met Office staff directly in future. Additionally confirming that the Cassley classification was “correct” did not answer my question of what classification it should be in given the previously noted system default was always Class 1 unless manually altered. A subsequent email to Karl Shepherdson for clarification was never answered. It would seem questioning the “Indisputable Truth” was not allowed.

So the mystery continues. Personally my view is that the site is completely inappropriate and its data should not contribute to the UK temperature record for climate purposes. Recording rare and highly site specific weather conditions, whilst interesting and locally relevant, should not influence the climate record.

Any reader’s contributions to increase the knowledge base on this distant outpost would be most welcome.

Source: https://tallbloke.wordpress.com/2024/08/31/cassley-dcnn-0343-foehn-and-other-effects/