The cold air ushered in by storm Xavier has certainly dropped the temperatures on the Zugspitze in the last 24 hours (fig 2). From a balmy max of 2.9°C yesterday, temperatures have quickly fallen away to around -9.1°C at 15 UTC this afternoon, but then again it is 9,718 feet up in the Wetterstein mountains in southern Germany close to the Austrian border. The strong northwesterly wind has died down a bit and they have had at least 20 cm of fresh snow during today, but how they manage to find any snow surface that’s not severely drifted to accurately measure a snow depth beats me.
Good quality observations have been coming in from Tampa every three hours overnight, it’s a great shame that the NWS don’t release the hourly observations that they must make. Forget about the position of Hurricane Irma and the contouring in this 09 UTC plotted chart (fig 1), at that time according to the NHC she was at 28.9° north and 82.6° west, with a minimum central pressure of 965 hPa, which is quite a way north of Tampa. I think it would be a good thing if most of the AWS in that part of the world are hardened/upgraded for the potential impact of a passing hurricane or occasional tornado. Observations from Key West stopped at 12 UTC yesterday, and the anemometer at Miami looks like it may have been severely damaged.
Believe it or not, the hourly weather observations from Ben Nevis from 1898-1902 have still not been digitised. It’s a real shame that the Met Office haven’t already done this on behalf of the nation, instead of relying on volunteers at Weather Rescue to do it for them (fig 2). But then again, they have their hands full, because they still have at least fifty years of climate records that the Victorians left them that also need digitising, because at the moment their climate records only extend back to 1910 for temperature and rainfall, and 1929 for sunshine. It’s not that the Met Office haven’t been round for all that length of time because they were established in 1854 as a small department within the Board of Trade by Vice-Admiral Robert FitzRoy, it’s just that when they did discover computers, they were too busy doing other things with them to bother adding the climate records that they held in the archives.
Personally I think as much effort that’s gone into digitising these records, ought to be put into to reestablishing the Observatory on top of the Ben. Well not exactly Observatory such as the Victorians built, more an automatic weather station, similar to the one on top of Cairngorm. I realise that there’s already a SIESAWS on Aonach Mor just across the Coire Leis from Ben Nevis, but its lower (1130 M), and simply doesn’t have the prestige of being sited on top of the highest mountain in Britain gives it. Power to the AWS would obviously be the main problem, and an extension lead 4,411 feet in length would simply be out of the question. Solar panels may help a little, but they would ice up easily and disappear under rime for most of the winter. A large rack of lithium-ion batteries may do it, but who would pay for them to changed by helicopter every month. A small wind turbine might do it but that again would ice up, maybe eventually some kind of fuel cell might be the answer for these remote places.
This is what the directors of the Scottish Meteorological Society said about the closure of the Ben Nevis Observatory in 1904:
“It is to the Directors a matter of profound disappointment that in this wealthy country it should have been found impossible to obtain the comparatively small sum required to carry on a work of great scientific value and interest, and that they are now obliged to dispose of the Observatory buildings and dismiss the staff”
It seems that little has changed in the last hundred years or more since its closure.
So if you have an hour to spare, why not volunteer your time to help digitise the Ben Nevis observations? I’m sure it won’t be long before the Met Office, in these days of financial austerity, see the potential in this idea, and will open up their archived observational records to volunteers to be digitised too!
Not such a perfect a start to Sunday in the southwest this morning, with a band of heavy rain moving slowly, but relentlessly eastward. Highest 12 hour rainfall totals till 06 UTC were at Johnstown Castle in County Wexford with 41 mm (fig 1). This was well forecast by the Met Office model as far as I see, but the intensity of rain we have seen in places may not.
Three or four green pixels around Penzance indicating estimated rainfall totals in the region of 32-40 mm till o6 UTC this morning (fig 2). The Met Office have come up with another classic analysis that only Salvador Dalí could have conjured up. A simple occlusion, warm front, upper cold front, cold front, occlusion kind of setup (fig 3). I’m afraid all that can I see in the observations is a warm front across the west of Cornwall at 09 UTC.
There seems to have been quite a bit of interest in the temperature difference between the very warm Tuesday (29th August) and the much cooler Wednesday (30th August) across the southeast of the UK. So I thought that I would add some more functionality to the “difference viewer” in my SYNOP application, so that as well as being able to produce a ranked table, I could produce a map of these plotted differences. I’ve still to add contouring to the map, but I thought I would publish the results of my efforts so far, so here without further ado are the differences in maximum temperatures [06-18] between Tuesday and Wednesday (fig 1).
As you can see from the table (fig 1), although Herstmonceux had a difference of 13.5°C yesterday (27.3 & 13.8), this was dwarfed by the differences across northern France, with Laval top of the list with a difference of 17.3°C between (34.9 & 17.6) which is 31.1° in Fahrenheit between the two days (fig 2).
I am surprised that some of the UK climate records used by the Met Office to calculate their global land temperatures for CRUTEM4 with, are from sites where the instrument enclosure, primarily the Stevenson screen, has been compromised over the years by the encroachment of buildings, car parks, and runways and the various ‘climate’ sites around the country, to such an extent that it must in some way be affecting the temperature sensors. Creeping urbanisation has been happening for years, and is not a new problem, it’s a bit like how politicians suddenly realised that life expectancy has been on the rise for the last 100 years.
Before I go any further these concerns have been voiced before, and a review of the observing sites of the UK has been done before, and much more thoroughly than I can do in this short article, most notably in the Surface Stations Survey by Tim Channon on the TallBloke blog.
The Surface Stations Survey work was done a few years ago now, and as far as I see wasn’t directly linked to the ‘raw’ monthly CRUTEM4 temperature data that you can freely download from the Met Office, and which is used to calculate a monthly estimate of global land temperature with. In recent years the Met Office, for some reason known only to themselves, have reduced the number of the UK sites from well over 100 twenty years ago (fig 1), to just 18 sites in 2017 (fig 2).
Here’s a graph (fig 3) of how the total number of UK sites that are currently used in the CRUTEM4 calculations has declined in recent years.
The irony of this 80% or more reduction in UK sites used, is that two of the three sites used to calculate the composite CET series, the longest instrumental record of temperature in the world, are now no longer used – Rothamsted (1872-2012) and Preston Moor Park (aka Stonyhurst 1960-2012).
Poor siting of instrument enclosures
But I digress, what I really wanted to
moan about bring to people’s attention was the precarious siting of the Stevenson Screen at some of the 18 sites that we still use to calculate a global temperature with. Generally the siting of the screen didn’t look too bad, but there are a number that are poor, and here are three of the worst sited Stevenson screens that I found using Google Maps. Of course guessing where the screen is an art that has become a bit of an obsession with me. The biggest offenders are all at airports, namely Aberdeen, Valley and the infamous Heathrow (figs 4, 5 & 6).
At this point I would like to say I wouldn’t be able to do this without Google maps, but I have noticed that the generally the quality of the highest zoomed images is inferior to those in the Google map images of the Surface Stations Survey. This might be just a Google maps issue, or it maybe a deliberate restriction on quality and zoom level requested by the MOD for RAF stations. The yellow circle is at a radius of 10 metres and the blue circle at a radius of 30 metres. I won’t go into detail of what I estimate the WMO classification for each site would be as regards temperature, I’ll just leave it your imagination.
What can the Met Office do about it?
When I was an observer every so often at an outstation, someone would come round and inspect the ‘met’ enclosure to see if it was being maintained correctly, I wish now that I had taken a keener interest in what the inspector was looking at other than if the bare patch had been weeded recently! I wonder if there was tick box to confirm that no jet engines were being run up within 30 metres of the screen? I can remember quite clearly being wafted by warm gusts of air from an F3 Lightning at Binbrook en route to the Stevenson screen across the pan to do the 09 UTC observation even in the middle of winter.
They could if they wanted to without much effort do the following with the climate records used from the UK in CRUTEM4:
- Reinstate the best of the climate stations that have been lost in recent years, but not the records from RAF Waddington or RAF Brize Norton please!
- Immediately reinstate the temperature climate records for Rothamsted and Stonyhurst, at the same time adding the one from Pershore, so that the three stations used for the renown CET series are included in the calculations, which to my mind would be only fitting!
- Remove Heathrow until the enclosure has been relocated possibly in the middle of Bushy Park!
This would be very easy for the Met Office to do, they wouldn’t have to go cap in hand to any other meteorological service to ask them to supply the data, as they already have those temperature records.
I know just how sensitive temperature sensors are in AWS these days, I have a Vantage Pro, and over the years I’ve relocated it a number of times in our garden, each location had its different weaknesses, too close to trees or the hedge, or too close to an area of paving, now it’s far too close to the garage. It certainly is a very difficult, if not impossible task to find a location on a modern airfield that’s totally unaffected by external influences on temperature. But in this day and age of advanced wireless communication, I just can’t believe it’s not possible to install AWS as far away as possible from any runway, car park, building or road, at any site, which invariably is at an airport, be it military or civilian. I’ve been doing it with my AWS without a problem for the last 13 years, albeit at a range of less than 10 metres! Inevitably this will have to be done as the demand for green space on airfield sites increases till the whole damn place is paved for a parking lot.
Exeter was narrowly the warmest place in the British Isles today with a maximum of 19.3°C, contrast that with the maximum of just 12.9°C at Kenley airfield in Surrey.
An apology to any residents of Liscombe who may be reading this before I start, because when I say – is Liscombe the dullest place in the British Isles? I mean with regard to sunshine and nothing else!
Liscombe, believe it or not, isn’t in Devon as I had always thought, but in Somerset. I forget that the county of Somerset stretches westward almost as far as Foreland point and Lynmouth in the west. The only reason I know about the village of Liscombe is that there is an AWS there, that generates hourly SYNOP reports (fig 1). Here’s a better look at the topography of the immediate area from the OS Map (fig 2). As you can see the Ordnance Survey have even marked where the ‘Meteorological Station’ is on the 1:50,000 map, which incidentally is at around 348 M above sea level, and almost due south of Winsford Hill (428 M) in the Exmoor National Park. I should imagine that hill see’s a good deal of snow in the right situation in winter, but must offer some protection to the village of Liscombe itself from the worst of any weather that comes in from the north.
Well the reason for the blog is that I suspect the sunshine totals are too low this year. Not a heinous crime I know, but I do think sunshine at Liscombe is a bit on the low side this year by quite a margin. I realise that a climate station at well over 1,100 feet does attract a lot of hill fog and upslope stratus, and I’m sure that’s quite a common feature of Winsford Hill in a southwesterly, but even allowing for that, the sunshine this year has been abysmally low. If you look at the sunshine totals across the UK there is usually a lower contoured area across Exmoor that seldom seems to be mirrored over the larger area of high ground over Dartmoor to the southwest in the first seven months of this year (fig 3). It could be the weather patterns have not favoured this part of Exmoor for sunshine of course, and maybe the map is skewed because there isn’t a climate station at a similar height and exposure on Dartmoor reporting sunshine.
All I know is that the sunshine totals at Liscombe since February have been 30% lower than at Exeter, just over 40 km to the south, which seems a wee bit too excessive to my mind (figs 4 & 5). Although as I’ve said sunshine at hill stations may be reduced by the incidence of hill fog and low cloud at times throughout the year, they do have one advantage over places lower down the valley especially in the autumn and winter months, they get off to a better start in the morning, because they often go unaffected by any radiation fog.
Here’s a map with the total number of sunless days (0.0 hours) of sunshine so far this year (fig 6).
As you can see from the map (fig 6) and the table below (fig 7) Liscombe so far this year has the highest number of dull days in the British Isles by some way, with 56 out of the last 235 days being without sun, second in the table is the nearby station of Camborne in Cornwall. By total sunshine accumulations, Liscombe is only the fourth dullest out of 55 stations. I have received 99% of the 06 UTC observation for Liscombe, so it’s not because they haven’t been transmitted.
What may be going on with the AWS at Liscombe, is that the sunshine sensor is somehow malfunctioning, perhaps not all the time, but enough to reduce the sunshine totals each day in some way, and without the Met Office perhaps even noticing. I do know that because there aren’t that many sunshine recorders across Devon, that the lower than average total is picked up on by the monthly sunshine charts (fig 3), as they are based on gridded data which the Liscombe observation will be used in.
Interesting news item from the BBC about the lingering snow patches in various gullies across the mountains of Scotland. I wonder if the three patches in the Cairngorms will survive? I suppose it will depend on the kind of Autumn that we are in for, cold and dry, or mild and wet. Just across the way from Ben Nevis is Aonach Mor with an AWS on it (WMO #03041). The AWS is not quite at the top of Aonach Mor which is 1221 M high (4,006 feet), but a little way down at the top of the chairlift at 1130 M (3,707 feet), from where I guess there is some kind of extension lead buried under the ground that connects the two. So temperatures should be not far off what they would be on the north face of the Ben, but of course that face would be in perpetual shadow.
OGIMET wouldn’t let me download last Autumn’s data for the AWS on Aonach Mor, but here is the thermograph from the 4th of January through to April (fig 3), and as you can see although it was sub-zero for extensive periods, it wasn’t overly cold, and January was notably mild.
The rainfall anomalies for the period between November 2016 and March 2017 were generally near average, with November being a dry month (fig 4).
The temperatures through the extended winter period where all above average, except for the dry November which was colder than average, December was exceptionally mild (fig 5).
Iain Cameron is correct when he says that the demise of the snow in the gullies of Ben Nevis was down to the lack of snow last winter. Snow is obviously dependent on rain falling with temperatures near or below freezing, and the lack of it was down to two things, colder periods also tended to be drier, and the wetter periods were also usually mild, a combination of the two meant that not enough snow fell to fill the gullies to survive through till the following Autumn.
I suppose if you coupled up the temperature from Aonach Mor with daily rainfall totals from Tulloch Bridge you could with a bit of jiggery-pokery estimate how much snow fell and accumulated at a 1000 M. With a few other bits of climate data you could also try to calculate how much snow was lost due to sunshine, evaporation, sublimation, and warm rain. It sounds like the job for a sophisticated NWP climate modelling tool as far as I can see.
It’s been an interesting week at Calvi in northwest Corsica weather wise. In the heatwave that’s been going on in that part of the world, there’s been a constant battle going on between the sea breeze from the north, and the foehn wind from over the mountains to the south (fig 3). The effect of the sea breezes arrival must be very noticeable at times, and must come as a welcome relief to the town (fig 1). It looks like the flip-flop between the two can happen at anytime of the day judging by the plot grid (fig 2), and the land breeze – sea breeze, must obviously be very finely balanced. Yesterday evening for example, the sea breeze which had set in earlier was quickly replaced by a land breeze that kicked in at 22 UTC and increasing the temperature from 26.3 to 31.6°C. The land breeze then failed early this morning at 02 UTC, and the temperature dropped again from 32.5 to 27.8°C, eventually the land breeze set back in at 10 UTC this morning as daytime heating cancelled out the sea breeze. I have marked out some other sharp fluctuations in the plot grid (fig 2).
The observing station at Calvi is located at the airport, in a valley a few kilometres to the southeast of the town itself (fig 3), with the Mediterranean sea to the north, and ringed by high ground to the south, east and west (fig 3).