Prestwick:Gannet WMO03136 – An analysis of combined adverse effects.

55.51545 -4.58474 Met Office CIMO Assessed Class 4 Installed 1/1/1993

Glasgow:Prestwick Airport has had Met Office weather stations in various different locations since its original construction/development in 1934 though the airfield had been in some form of use as far back as 1913. It is a mixed military and civilian resource being particularly favoured by the Canadian and US Air forces with the latter using it as the preferred Scottish landing location for Air Force One. The Met Office weather station, as is the case at nearly all operational airfields, is not suitable for aviation purposes. Prestwick handles its own meteorological office covering the disparate needs of this unusually laid out airport with longer runways at almost right angles. It is worth noting the name “Gannet” comes from the former Royal Navy Air Service name of HMS Gannet and was home to the “Sea King” Helicopter fleet.

The most obvious feature from the headline image does rather stick out like a sore thumb, or more accurately a large “H”. Firstly though to analyse the rest of the site requires delineation of the dimensions.

It is slightly ironic that this site could theoretically meet Class 3 standards and indeed Tim Channon did make that assessment in his 2012 review though back then that big H had not been painted on the tarmac. { n.b.was it not used as such back then? ) https://tallbloke.wordpress.com/2012/09/01/wmo03136-prestwick-gannet/

The site does not appear to fall into sun shade for any significant time but in common with so many sites the surrounding buildings and fences may well act as wind breaks creating static air in the naturally aspirated screens used by the Met Office. The StreetView image highlights this likely effect.

This wind break effect cannot be ignored. Above is a razor wire topped 2.4 metre high security fence with close mesh wire just 6 metres from the enclosure which is similarly enmeshed with a 1.2 metre wire surround. As a comparison a local garden centre to me has an area surrounded by a close run tape barrier also about the same height. Inside that is a lower similar tape barrier close to the plants on low benches. Even on windy days this inner (and un-roofed) customer area has almost completely static air quite deliberately engineered to protect the plants. Sites like this by a roadside with the wide gravelled security area inside, large areas of apron tarmac, significant buildings and aircraft hangars are completely unnatural and will lead to distorting effects.

Considering this static air effect, though, that big “H” will certainly stir up things rather a lot when in use – and it very often appears to be judging by historic images, Google aerial and Bing streetside examples below.

In my review of Heathrow the issue of Aitken Effect was shown to be a well known problem which research at Reading University evaluating over recording errors and stated “We estimated that across Europe about 4% of maximum temperatures will be affected in this way, and about 12% of recorded minimum temperatures.” This was based on tests carried out at the CIMO Class 2 Reading Whitenights facility not the hugely more common low grade Class 4 or 5 sites that dominate the UK (and probably European) networks. Furthermore as Dr Eric Huxter highlighted in his evaluation of PRTs the propensity to over record in specific weather conditions is probably significantly under estimated. These points were also confirmed by ex Met Office senior manager John Maynard in his metrology post.

Evaluating the effect of helicopter take offs, over flying of the screen and landings needs to be considered. Given the large number of sites the Met Office operates in the immediate vicinity of helipads it would be appropriate for them to have performed suitable research, unfortunately there is none that I can find. Resorting to AI it also found no significant research even though it recognised both the “rotor wash” and engine exhaust heat should have readily measurable effects. Looking to the Talkshop’s own knowledge resource base in lieu , as Joe Public commented on the Brize Norton review

“Newton’s third law springs to mind: for every action there is an equal and opposite reaction.

Even empty, the Antonov An-225 Mriya weighs 285,000 kg. The term ‘aerodynamic’ is relative; so a significant volume of air must be shifted out of the way, for the beast to make progress down the runway.

To get that beast to move, involves pushing the medium of air having a density of 1.222 kg/m^3 as the “equal and opposite reaction”. So an awful lot of air at a relatively high speed, gets ‘thrown’ a great distance.”

The helicopter in the Streetside image above is an Augusta Westland AW159 Wildcat with a maximum take off weight of 6,000 kg thus it means a shifting a minimum of 4,900m^3 of air just to get it moving upwards off the ground. Not quite Antonov An-225 standards but still a massive amount when the helicopter is just 50 metres away and then potentially flying directly overhead. The unsuppressed exhaust gas temperature at take off can reach 900 °C. Whichever way this is looked at there are major factors which will unquestionably (whatever unsubstantiated claims the Met Office may make) artificially elevate readings.

This all then comes to the compounding effect of all the above by the simplistic system of averaging used by the Met Office as detailed by Stephen Connolly. Tmax +Tmin ÷ 2 is always going to be prone to raised distortion caused by the registering of a PRT of a transient raised spike (helicopter activity) and the occasional raised overnight minimum from Aitken effect.

The two effects are in addition to all the other modifying effects of a poor Class 4 site and the inevitable UHI of an airfield alongside the expanding town of Prestwick itself. These types of sites are effectively only measuring changes in site conditions over time, changing activities on the site over time, changes in instrumentation and developing UHI. Actually measuring the “change” in the meteorological climate seems a secondary concern to actually producing accurate data to confirm or deny that change.

Source: https://tallbloke.wordpress.com/2025/06/15/prestwickgannet-wmo03136-an-analysis-of-combined-adverse-effects/