There was an intense positive mean temperature anomaly over the Chukchi Sea during December 2017. It’s no wonder that Anchorage saw the 5th mildest December on record.
A massive contrast in temperature anomalies between the exceptionally cold east of North America (-14°C), and a tongue of warm anomalies that extends from northern Russia (+17°C) southwest across Europe to Iberia, during the first six days of the New Year as you can see in this chart (fig 1).
If we do see an easterly anticyclonic spell in the next few weeks the temperatures may not be as cold as usual in the UK, because the source of that cold continental air has been very mild throughout this autumn and early winter. At the moment Moscow isn’t reporting a snow depth, because there isn’t any, which in itself is uncommon at the turn of the year (fig 1), in fact the mean temperature there has been anomalously warm since the start of November. The chart of snow and ice cover for the northern hemisphere (fig 2) illustrates the lack of snow. In the last twenty years a chart similar to this one has become a common feature of many a winter.
Here are the anomalies so far this month for our part of the northern hemisphere, as you can see there is a large positive +5°C anomaly across western Russia, so it’s no wonder there’s not much snow in Moscow (fig 3).
As far as I can see using the daily objective LWT data that I regularly download from the UEA, the 30 percent NW’ly weather types of the last month (7 November – 6 December) are the highest percentage for this period ever seen in the series since it started in 1871 (fig 1). Thirty percent may not seem high but NW’ly types are not a common LWT believe it or not.
Here are the 00 UTC weather charts for the last month (fig 2), and as you can see southerly and southwesterlies have been in short supply.
So the obvious question is with so many NW’ly days during the last month why has the weather been so mild, and not much colder? The last months CET daily mean values (9 November – 8 December) are currently a shade above average at +0.18°C above the long-term 1981-2010 average (fig 3). Even during the first eight days of December, mean temperatures across Central England are currently still +0.75°C above average.
It may have a lot to do with the sea surface temperatures around our part of the northeast Atlantic and they are currently much warmer than average (fig 4).
Here are the 12 UTC temperature anomalies for the start of December for our part of world (fig 5), which show that colder than average temperatures are in short supply even when we are currently in the grips of an Arctic northerly across the British Isles. So the answer to the question why hasn’t the last month been colder, is simply down to the fact that surface temperatures across the world are currently at record high levels, and no matter how many northerly outbreaks we seem to have seen in the last month it seems to have made little difference.
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.
Fascinating anomaly chart for the first two weeks of August 2017. A band of cold anomalies more or less stretches from central north America, across the north Atlantic, to northwest Europe, with anomalies ranging from zero to -2°C. The recent heatwave across southeast Europe has left its mark there, with a belt of positive anomalies, as warm as +6°C over the Ukraine and eastern Black Sea, and curving down through Iraq, Saudi Arabia and into Sudan.
The extremely high temperature anomalies seem for the moment at least seem to have disappeared from the Arctic. This temperature anomaly chart (fig 1) is for the first 15 days of May 2017, and yes anomalies are still mainly positive in the Arctic, but in a range -2°C to +6°C, rather than in excess of +16°C that they were back in January and February. That might explain why Arctic sea ice has staged a bit of a recovery during late spring. There are a number of anomalous cold areas, one north of the Great lakes in Canada (-4°C) and another one over Scandinavia and northeast Russia (-6°C), the latter causing problems with heavy late spring snowfalls in places. Central North America, Greenland and large parts of central Asia have seen a very warm spring with anomalies typically +4°C above the 1948-2014 long-term average.