Writtle DCNN3644 – Demonstrating a decline in standards

51.73351 0.42911 Met Office CIMO Assessed Class 4 Installed 1/1/1940

Although not a WMO reporting site, Tim Channon reviewed this site in 2013 and at the time judged the site as Class 4. It is worth considering Tim’s review in respect of the changes over just those intervening 12 years and the way the site’s standards have deteriorated. https://tallbloke.wordpress.com/2013/04/27/surfacestation-writtle/

Tim always accurately delineated circled areas around the screen as his original below from 12 years ago.

The site was getting close to having a serious shading problem from the south around to west with changing ground cover predominantly to the east. Compare that to this May 2024 image with bushes now growing even within the 3 metre radius downgrading the site to Class 5.

Surely at this point the Met Office inspection team would consider either moving the screen or getting the site owners (Writtle College – an agricultural training centre) to attend to the bushes to improve the situation. The compound is unusually large making it hard to see why the issue cannot be improved. The Streetview image adds the height dimensions showing this site is now unacceptable. Compare this image to the one Tim included in his report and the growth stands out notably.

The base of a Stevenson screen is normally set at 1.2 metres above ground level (though this one looks suspiciously low) which implies those nearby shrubs are over 2.5 metres tall causing multiple problems. The field use tracks also indicate (similar to nearby Cavendish) multiple passes and slow turnings of tractors which modern PRT sensors are readily able to quickly respond to any transient exhaust heat pulse. It is worth noting that World Meteorological Organisation guidelines are that PRT readings should be averaged over 5 minute periods – the Met Office does not meet this standard and only averages the PRT continuous output readings over a 1 minute period. Writtle was automated (thus converted from observer read Liquid in Glass instrumentation to PRT) in 2009.

It is highly notable that Writtle is now a regular star performer in the daily “extremes” stakes for both regional and national highs. Perhaps the increasing surrounding wind breaks are leading to more regular low wind speed Aitken Effects over heating the sensors. The same effect is noted at Heathrow where the Stevenson screen has become increasingly enclosed over time.

These “Daily Extremes” bring home an interesting point – here is yesterday’s offering.

So when is a “Region” not a “Region”? Who decided that Writtle in Essex just west of Chelmsford is not in the same “Region” of London and South East England but that Brize Norton nearer the Welsh border than London somehow is? This smacks of civil service regional administration areas rather than meteorological comparisons. The Met Office regional comparisons make for fascinating reading when taken out of this “extremes” context and into “averages”

The first four presumably comparative stations are indeed in the same defined region though quite how useful the Zombie Stanford-le-hope station that died in 1983 can actually be is open to much debate. Peculiarly Gillingham No 2 is NOT in that East of England region but still considered a good comparison despite similarly having closed down and died 44 years ago in 1981 and being 24 miles distant over the other side of the Thames Estuary. Perhaps by this logic, Langdon Bay (Dover) should have comparatives in Boulogne-sur-Mer …….maybe they do!

To add further confusion clicking on the Writtle data link gives averages for “Districts” with this one being in “East Anglia” and the Region being “England South” Confused? Well perhaps that is part of the intention. All that can be said is that perhaps the Met Office should “stick with the day job” look after their weather stations in a more appropriate manner and try to produce accurate meaningful data rather than neglecting them.

Source: https://tallbloke.wordpress.com/2025/06/09/writtle-dcnn3644-demonstrating-a-decline-in-standards/