By John Adams, current observer at St Harmon 2.
When we first arrived in St. Harmon the local farming community were very quick to inform us that we had moved to the coldest place in Wales, if not the whole of the United Kingdom. Some of them even sounded proud of the fact, but it was certainly not something we had given any consideration to ourselves before coming here. Being keenly interested in meteorology since a young child I was curious. A little investigation revealed that there used to be a Met Office climate and auxiliary observing station in the village during the 1980’s. On searching through the records on the Met Office website it soon became apparent that St. Harmon featured far more frequently in the list of coldest nights than one would normally expect. At the same time I had also observed from WOW that there was a hole in the observing network around Mid Wales, even in respect of personal weather stations. This is the story of my quest to establish whether St. Harmon really is the coldest place, and to try and fill the hole in the observation network, first with my own personal weather station and subsequently establishing St. Harmon no.2 voluntary climate station under the auspices of the Met Office.
For as long as I can remember, and probably going back to the days when I was still at Primary school, I have had an interest in the weather. Long before leaving school I had started keeping a daily record of the weather in our back garden.
My very first rain gauge was a rudimentary affair, possibly even the product of a ‘Blue Peter’ project. I’d used my pocket money to purchase a 5 inch plastic funnel from the local hardware store. This was supported on a cut down plastic bottle buried in the ground so that the rim was at the correct height, and the rainfall caught in another bottle. I can’t remember how I used to work out the amount of rainfall from the amount of water collected until eventually I was able to source a proper measuring flask.
Temperature, max and min, was recorded using a very simple garden max and min thermometer, mounted on a wall where the sun never shone. This eventually progressed to the Met Office standard mercury in glass, as it was then, thermometers, but still mounted on the wall. A proper Stevenson screen would have been way beyond my budget.
Throughout my childhood there was nothing that I would have liked better then to have had my own screen and set of thermometers, anemometer and wind vane, proper rain gauge and the absolute bees knees would have been a Campbell Stokes sunshine recorder.
Leaving school at 18 I thought my fortunes had changed, with a real opportunity to pursue this passion. I had landed a job with the Met Office! The post was as an assistant in the forecasting office in Bracknell. This I quite enjoyed for a while and received training as an observer, but, as a relative youngster began to feel that what was effectively an office based job was not what I wanted from life. So, after a few years, and totally on the spur of the moment handed in my notice. To this day I’m unsure whether this was a wise decision, or whether I should have directed my career into an aspect of the Met Office which I would have found more agreeable.
But, decision made, I ended up drifting for a while before taking a job as a temporary Christmas casual with another bastion of British society, Royal Mail. Christmas came and went and over 30 Christmases later I took retirement, having moved to St Harmon during that time and established our own holiday accommodation business.
When first moving here I was totally unaware of the unique
geography of St Harmon, and the Marteg valley, giving it it’s own micro-climate
and a reputation, especially amongst the locals, of being the coldest place in
Wales, if not the whole of the UK.
As this photo, taken from the top of Cwmythig Hill shows, this very rural community sits in a bowl at about 300m above sea level surrounded by hills, some reaching just over 500m asl. The only outlet from this bowl is where the river flows through the Gilfach, a narrow U shaped valley just off to the left of the picture, leading down to the River Wye. As a consequence the cold air associated with a still night rolls down into the valley bowl and is then unable to escape.
Quite soon after arriving here I found out that the Met
Office used to have a climate station in the village. Further research revealed
that a rain gauge belonging to Welsh Water had been sited at the Post Office in
St Harmon since 1961 with the Met Office subsequently enhancing it as an
auxiliary observing site.
Full synoptic observations commenced on 4th October 1982, the station (03505) scheduled to report at 09Z, 12Z, 15Z and 18Z Monday to Saturday and 09Z and 12Z on Sundays with a climate report daily at 09Z. This continued up until December 1986 when the property was sold, with the new owner resuming observations on 14th January 1987 following the same schedule as before. This appears to have continued through until October 1991, when the station condition was assessed as unsatisfactory and it closed on 1st November 1991, with no apparent reason being specified.
So ages was spent trawling the Met Office website, trying to find out more and satisfy myself whether this really is the coldest place, eventually coming across a table showing the monthly extreme minimum temperature values for Wales, shown below. This further intrigued me, noting the number of times that St Harmon has recorded the extreme minimum temperature for Wales, and especially so during the summer and autumn months, rather than the winter.
|
Month |
Value |
Location (Wales) |
Date |
|
January |
–23.3 °C |
Rhayader (Powys) |
21 January 1940 |
|
February |
–20.0 °C |
Welshpool (Powys) |
2 February 1954 |
|
March |
–21.7 °C |
Corwen (Denbighshire) |
3 March 1965 |
|
April |
–11.2 °C |
Corwen (Denbighshire) |
11 April 1978 |
|
May |
–6.1 °C |
Alwen (Conwy) |
1 May 1960 |
|
Alwen (Conwy) |
3 May 1967 |
||
|
St Harmon (Powys) |
14 May 1984 |
||
|
June |
–4.0 °C |
St Harmon (Powys) |
8 June 1985 |
|
July |
–2.5 °C |
St Harmon (Powys) |
9 July 1986 |
|
August |
–2.8 °C |
Alwen (Conwy) |
29 August 1959 |
|
September |
–5.5 °C |
St Harmon (Powys) |
19 September 1986 |
|
October |
–9.0 °C |
St Harmon (Powys) |
29 October 1983 |
|
November |
–18.0 °C |
Llysdinam (Powys) |
28 November 2010 |
|
December |
–22.7 °C |
Corwen (Denbighshire) |
13 December 1981 |
|
ST HARMON |
25-DEC-85 |
-1 |
|
ST HARMON |
26-DEC-85 |
-0.3 |
|
ST HARMON |
27-DEC-85 |
-5.6 |
|
ST HARMON |
28-DEC-85 |
-12.2 |
|
ST HARMON |
29-DEC-85 |
-12.2 |
|
ST HARMON |
30-DEC-85 |
-12.4 |
|
ST HARMON |
31-DEC-85 |
-3.8 |
|
ST HARMON |
01-JAN-86 |
-3.8 |
|
ST HARMON |
02-JAN-86 |
-3.2 |
|
ST HARMON |
03-JAN-86 |
-2.5 |
|
ST HARMON |
04-JAN-86 |
-9.4 |
|
ST HARMON |
05-JAN-86 |
-8.1 |
|
ST HARMON |
06-JAN-86 |
-7.5 |
|
ST HARMON |
07-JAN-86 |
-7.5 |
|
ST HARMON |
08-JAN-86 |
-2.5 |
|
ST HARMON |
09-JAN-86 |
-2.6 |
|
ST HARMON |
10-JAN-86 |
-1.4 |
|
ST HARMON |
11-JAN-86 |
1.7 |
|
ST HARMON |
12-JAN-86 |
1 |
|
ST HARMON |
13-JAN-86 |
1.8 |
|
ST HARMON |
14-JAN-86 |
2.2 |
|
ST HARMON |
15-JAN-86 |
-0.5 |
|
ST HARMON |
16-JAN-86 |
-4.1 |
|
ST HARMON |
17-JAN-86 |
-3.5 |
|
ST HARMON |
18-JAN-86 |
-1.4 |
|
ST HARMON |
21-JAN-86 |
2 |
|
ST HARMON |
22-JAN-86 |
-0.8 |
|
ST HARMON |
23-JAN-86 |
0 |
|
ST HARMON |
24-JAN-86 |
-3.6 |
|
ST HARMON |
25-JAN-86 |
-6 |
|
ST HARMON |
26-JAN-86 |
-8 |
|
ST HARMON |
27-JAN-86 |
-2.5 |
|
ST HARMON |
28-JAN-86 |
-2.5 |
|
ST HARMON |
29-JAN-86 |
-1.8 |
|
ST HARMON |
30-JAN-86 |
-2.6 |
|
ST HARMON |
31-JAN-86 |
-1.6 |
|
ST HARMON |
01-FEB-86 |
-2 |
|
ST HARMON |
02-FEB-86 |
-0.5 |
|
ST HARMON |
03-FEB-86 |
-2.2 |
|
ST HARMON |
04-FEB-86 |
-3 |
|
ST HARMON |
05-FEB-86 |
-5 |
|
ST HARMON |
06-FEB-86 |
-7.5 |
|
ST HARMON |
07-FEB-86 |
-6 |
|
ST HARMON |
08-FEB-86 |
-7.5 |
|
ST HARMON |
09-FEB-86 |
-13.2 |
|
ST HARMON |
10-FEB-86 |
-10.8 |
|
ST HARMON |
11-FEB-86 |
-12.3 |
|
ST HARMON |
12-FEB-86 |
-6.8 |
|
ST HARMON |
13-FEB-86 |
-7 |
|
ST HARMON |
14-FEB-86 |
-7 |
|
ST HARMON |
15-FEB-86 |
-6.8 |
|
ST HARMON |
16-FEB-86 |
-4.5 |
|
ST HARMON |
17-FEB-86 |
-6 |
|
ST HARMON |
18-FEB-86 |
-5.4 |
|
ST HARMON |
19-FEB-86 |
-10.5 |
|
ST HARMON |
20-FEB-86 |
-9 |
|
ST HARMON |
21-FEB-86 |
-16 |
|
ST HARMON |
22-FEB-86 |
-11.7 |
|
ST HARMON |
23-FEB-86 |
-7.6 |
|
ST HARMON |
24-FEB-86 |
-7.7 |
|
ST HARMON |
25-FEB-86 |
-6 |
|
ST HARMON |
26-FEB-86 |
-6 |
|
ST HARMON |
27-FEB-86 |
-7 |
|
ST HARMON |
28-FEB-86 |
-5.5 |
|
ST HARMON |
01-MAR-86 |
-3.6 |
|
ST HARMON |
02-MAR-86 |
-5.5 |
|
ST HARMON |
03-MAR-86 |
-11.5 |
|
ST HARMON |
04-MAR-86 |
-5.8 |
Further examination of the 1986 Monthly Weather Reports also show surprising minimum temperatures during the months of July (below top) and September (below bottom).
These are examples from one year alone, and by spending time searching the Met Office archives many other similar examples can be found.
Whilst below freezing minimums during winter would be
considered normal I was surprised by the frequency of minimum temperatures
below freezing during the summer months, as shown by the tables below for just
3 months of the year, June, July and August, and indicating that a frost can be
expected at any time of year.
This led to a desire to try and continue the records, and in addition, by looking at WOW there appeared to be a large hole in the observing network over Mid Wales, not just with the official sites but also personal weather stations.
So in 2012 I invested in a Davis Vantage Vue, mounting it on a pole as high as I could get it. However the setup, with all sensors contained in the same housing, inherently creates inconsistencies with the rain gauge and thermometer way above ground level. Siting of the device also proved problematic and frustrating, with it failing to maintain contact with the console, which itself needed to be connected to a mini pc and internet, when positioned where it would have almost ideal exposure to the weather. Of necessity it had to be directly in sight and close enough to the house and as a consequence the site chosen was far from ideal, almost completely sheltered from the east and south, although better exposed in other directions.
A few years later I decided to upgrade to the Davis Vantage
Pro, thinking that this would permit the rain gauge and temperature sensors to
be sited at a better height above ground, whilst the anemometer could be sited
in a more exposed location. This also proved more difficult than expected, with
the range for reliable radio contact turning out to be even less than that of
the Vue, resulting in the temperature sensors and rain gauge being sited even
closer to the house and more sheltered than before. The only real advantage was
slightly better exposure for the anemometer, which did not seem to suffer the
same problem.
Nonetheless, this setup has been reporting to WOW and Weather Underground ever since as Woodhouse, St Harmon. The site is about 2 ½ km from the site of the original Met Office station. Even with the obvious shortcomings -12.4C was recorded on 12th December 2017, and the data has provided a continuation of the data collected at the former station.
For a simple comparison of accuracy on 25th January 2021 a low of -10.5C was recorded by the Vantage Pro, which compares to a low of -10.8C recorded by the official Met Office equipment. As a general rule any discrepancy appears to be less than 1 degree and generally around 0.3 between the two sets of observations.
However, I have never been completely happy with the setup, but cannot justify the considerable additional expenditure for repeater stations to allow the sensors to be better sited. Throughout I had always wanted maximum possible accuracy and proper recognition.
By chance one evening I was randomly looking around the Met Office website and spotted a little mention that they were looking for suitable climate station sites and observers. So I followed the link and sent off an email offering the site at the bottom of our field, exactly where I had originally intended to site the personal weather station.
I heard nothing for several months, then, out of the blue I
had an email from Stuart, regional network manager for Wales and the South
West, thanking me for my email and asking if I was still interested. Naturally
my answer was ‘yes’ and so it was that we were setting the official climate
station up in early 2018 to record temperatures, rainfall, sunshine and of
course a daily synoptic observation at 0900 each morning.
Readings have subsequently been on an almost daily basis; there have been a few occasions when this has been impossible, and already the data gathered has provided an interesting and worthwhile continuation of the data collected at the former St. Harmon station, and an ongoing confirmation that St Harmon is consistently the coldest place in Wales. In a list of the coldest nights in Wales and South West England between December 2019 and November 2020 St Harmon features no less than 10 times, with the all time record May low of -6.2 on 14th. This, by coincidence, coincides exactly to the day with the previous all time low of -6.1C on 14th May 1984!
|
LOWEST MIN TEMPS |
|||
|
SITE |
OB DATE |
MIN TEMP |
|
|
ST HARMON NO 2 |
02-Dec-19 |
-6.5 |
|
|
ST HARMON NO 2 |
27-Mar-20 |
-6.4 |
|
|
ST HARMON NO 2 |
19-Jan-20 |
-6.3 |
|
|
ST HARMON NO 2 |
14-May-20 |
-6.2 |
|
|
SWYDDFFYNNON |
02-Dec-19 |
-6.1 |
|
|
MARNHULL |
21-Jan-20 |
-6 |
|
|
SENNYBRIDGE NO
2 |
02-Dec-19 |
-6 |
|
|
ST HARMON NO 2 |
20-Jan-20 |
-5.9 |
|
|
ST HARMON NO 2 |
26-Mar-20 |
-5.8 |
|
|
ST HARMON NO 2 |
12-May-20 |
-5.7 |
|
|
ST HARMON NO 2 |
06-Feb-20 |
-5.6 |
|
|
TRAWSGOED |
02-Dec-19 |
-5.4 |
|
|
ST HARMON NO 2 |
14-Apr-20 |
-5.3 |
|
|
YEOVILTON |
19-Jan-20 |
-5.1 |
|
|
LIBANUS |
02-Dec-19 |
-5.1 |
|
|
ST HARMON NO 2 |
21-Jan-20 |
-5.1 |
|
|
FONTMELL MAGNA |
21-Jan-20 |
-5 |
|
|
LLANFYNYDD |
02-Dec-19 |
-5 |
|
|
LLYSDINAM |
02-Dec-19 |
-5 |
|
Whilst not showing the absolute minimum for the night, the
all time low was also quite clearly depicted on the WOW chart for 05.00 on the
morning of 14th May 2020, with the temperature well below all the
neighbouring stations.
Another instance of St Harmon being the coldest place
occurred even during the time when this blog was being prepared, on 28th
February 2021, and is clearly represented on the WOW chart for 09.00 on that
morning (below). This was another morning with still conditions resulting from
high pressure.
Interestingly though, whilst frequently coming up as the coldest in Wales none of the minimums from either my PWS or the official climate station are as low as many of the readings from the original station, as shown by a simple comparison between the tables above for June, July and August at the original station and those below from St Harmon 2.
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