Porthmadog DCNN 7750 – More Multiple Met Office mismanagement and misrepresentation

52.91454 -4.15807 Met Office CIMO Assessed Class 4 Installed 1/1/1993

Porthmadog weather station is not in Porthmadog (or even “Port Madoc” as it was sign-posted when I went there as a child) but by the seaside at Morfa Bychan situated on the local golf course. It represents all that is bad about Met office weather stations in location, maintenance and data representation. it is also a stand out star for reporting occasional infrequent weather events so that makes it an obligatory inclusion for the Met Office.

This below is a fairly common headline event for selected weather stations in parts of Wales and Scotland and also those by long beaches and sandy soils.

The North Wales area, in common with parts of Scotland, is notorious for registering Foehn Effects as detailed by Oldbrew here https://tallbloke.wordpress.com/2019/12/30/scottish-highlands-experience-16-8c-december-temperature-record-due-to-the-foehn-effect/ . This effect has resulted in both the UK December and January highest temperatures being recorded at Achfary in Sutherland. Similarly the Guardian newspaper reported the effect turning North Wales into a somewhat unlikely winter holiday destination.

Weather stations such as Prestatyn, Rhyl and Llandudno regularly claim daily highs especially in winter months. There is nothing at all wrong in recording such occasional weather events and they are important features to study. However, such weather events do not reflect the climate of the UK as a whole and including them in the climate record only distorts any natural trends. There is enough “noise” in the data without adding such one-off occurrences.

However, there are other effects of siting at play with the current Porthmadog site recording these highs in early May. This wide angle view highlights the point.

The whole area is either sandy soil, beach or inland bare sand. Parts of the golf course look almost like a continuous sand bunker. Any extended period of dry weather and areas like these become tinderbox dry and, in the absence of water having to be evaporated, will warm up very rapidly by day. Yesterday’s regional high is quite normal for Porthmadog in these conditions. By the same token such locations will normally rapidly cool by night but only in the open countryside.

A known flaw with Stevenson Screens is that at low wind speeds i.e. <1 metre per second (3.6 kmph> Heathrow researchers at the University of Reading were reported to have established this flaw accounted for – “1% of cases where the differences greater than 1°C. We estimated that across Europe about 4% of maximum temperatures will be affected in this way, and about 12% of recorded minimum temperatures.”

The above findings were observed under test conditions at the Reading University Weather Station which is obviously exceptionally well maintained being probably the UK’s most important meterological education centre. Such low wind speeds are relatively uncommon in the UK’s open maritime climate but not so rare if the area surrounding the screen has been either deliberately (Walled Gardens) or inadvertently (overgrowth) converted to a major wind break.

This is the historic image of Porthmadog not long after original instalation.

There was no enclosure around the screen, neither were there any shrubs nor trees in the immediate surrounding area. There was a 10 metre radius clear of obstructions – Class 4 just about. Now, however, as the headline image demonstrates the screen is virtually surrounded to the north, east and south by dense conifer and to the south west by an ever increasing heat island of dense housing. This site is now unquestionably Class 5S and thus completely unusable for any climate reporting. On the day of the above regional high the nearest wind readings revealed very low wind speeds at 10 metres of open and exposed height and dead calm overnight for periods even at ultra windy clifftop Capel Curig at 216 metres amsl.

How this deterioration of the Porthmadog site has come about probably lies in this deliberate planting of windbreaks for the benefits of those using Porthmadog Golf Club. The image below is the only clear Street View one and dates from 14 years ago in 2011. Conifers grow quickly and it is these that have caused the current poor lack of open area around the screen.

Surely the Met Office must be aware of the problems at this site and should have taken steps to either improve it or re-locate the screen – continuing to use almost certainly inaccurate readings is unacceptable.

Then things get worse, when reviewing sites I routinely look at how the data is portrayed in terms of long term averages. Porthmadog was established 32 years ago and could well warrant a climate average over the standard accepted 30 year period. As so often the Met Office declines to offer such figures but offers alternative sites – these offerings were incredibly bizarre for Porthmadog.

Cwmystradllyn (3 miles away) has temperature records starting 1/4/1974 and ending 31/12.1982 – barely over 8 years of data which was very poorly recorded – most of those few years had more than 10% missing days but far more ridiculous was the accuracy of reporting. For reasons only known to the Met Office, who give averages to the second decimal place, the Cwmystradllyn observers did not even bother to take readings to the FIRST decimal place. This is a perfectly typical example of the site readings seemingly untroubled by too much accuracy. Columns I and J represent maximum and minimum temperatures…………very approximate indeed but apparently good enough for 60 year average calculations.

If comprising rolling 60 year climate averages based on just that short period of dodgy data seems remarkably contrived then consider Llanbedr – temperature readings started on 5/2/1998 and ended 1/11/2004, not even 7 years of readings. I believe the modern expression is “YCMIU” – less than 7 years incomplete data is good enough for a 60 year extrapolation to the one hundredth of a degree?

Cwymstradllyn, below, had died 9 years before this climate reporting period even started. If readings are to be kept from “well correlated” stations then why not simply use Porthmadog itself to continue the readings? Or is that too difficult a question to answer?

Naturally, I shall be asking these very reasonable questions to identify exactly which stations are being used to contrive these figures. If the Met office cannot or will not answer then I feel it is reasonable to discount these types of figures as fictional junk……But will the Met Office listen?

Source: https://tallbloke.wordpress.com/2025/05/08/porthmadog-dcnn-7750-more-multiple-met-office-mismanagement-and-misrepresentation/