The snowfall of February and March 2018

I thought that I would take a retrospective look back (excuse the tautology) at the last two cold snaps that we’ve had, and some of the snow depths that were reported by various AWS around the country. The graphs show accumulated and fresh snow depths that I’ve gleaned from SYNOP reports which in the UK helpfully include hourly snow depths (NWS please take note). The blue bar chart in the graph represents fresh snow, that is the difference in snow depth between each hour, red bars indicate snow melt, and the light blue bar series is the hourly snow depth. Bars that span more than an hour are because I’m missing those observations.

From the recent cold spell that started last weekend (17th March) I’ve included the chart for Dunkeswell in Devon (fig 1) and High Wycombe in Buckinghamshire (fig 2).

Figure 1

As you can see the snow on the higher ground of Devon (Dunkeswell 252 m amsl) will do well to survive much longer than four days, all though the deeper drifts on the moors will last longer. You can see why the heavy snow on the morning of the 18th at High Wycombe caught the Met Office out, with the bulk of the 27 cm falling in just two hours (fig 2).

Figure 2

Here are three charts from the much longer and severe cold spell that started at the end of February 2018:

Figure 3

The snow came quite late to St Athan in south Wales (fig 3), but when it did come overnight on the 1st and 2nd of March, it did it in style and put down 56 cm before it had finished. That amount of snow took a whole week before it thawed away completely.

Figure 4

The snow at Wittering in Cambrigeshire started on the evening of the 26th and came in a couple of batches, with a maximum depth of 37 cm by the 3rd of March (fig 4).

Scotland also had a lot of snow, as these next two graphs testify. The first is from Bishopton in Glasgow, where a maximum depth of 46 cm was reached on the morning of the 2nd of March (fig 5).

Figure 5

Finally here’s the snow graph for Drumalbin a weather station on a low hill in south Lanarkshire, where 55 cm or more of snow had accumulated by the 1st of March (fig 6).

Figure 6

I’m sure these laser measured snow depths are very accurate, but in both snow events the wind was strong and there was a lot of severe drifting going on, so how representative these depths are is open to question.

The trouble with automatic weather stations in cold weather

Figure 1 – Courtesy of the Met Office and Weather for Schools

Automatic weather stations now make up nearly all the network of observing sites in the UK, and they all have an inerrant problem when it comes to reporting precipitation totals in very cold weather, and that is they can’t!

Precipitation from AWS

Have a look at the 12 hourly totals [18-06] from 06 UTC this morning from across the country (fig 2) and you’ll see that almost all stations are reporting no more than a ‘trace’ of precipitation. These accumulations are obviously incorrect because most of the precipitation that’s fallen in the form of snow will still be stuck, frozen in the funnel of the gauge. Some AWS sites do have snow depth sensors, but these are not the answer, and can be easily fooled as we have seen this winter, by drifting when the wind is strong enough to lift any snow that has fallen.

Figure 2
Weather Radar

Here’s are my estimates from the radar network of the precipitation that has fallen since 06 UTC on Saturday morning (fig 3). If this is anything to go by then, the deepest of the snow looks to have fallen across Norfolk and Suffolk in some kind of convergence zone, with precipitation totals as high as 16-24 mm. I estimate that there was around 6.9 mm from around High Wycombe, which I realise is not enough to account for the 27 cm of snow there at the moment. In my defence I offer the “spoking” that’s evident from the Chenies radar. Chenies lies not so many miles E’NE of High Wycombe, and I did speculate last year that the “spoking” that occurs there at times is caused by the radar being blocked by some of the large trees that surround the site.

Figure 3
One solution

I don’t know enough about why this is such a problem in the 21st century, you would have thought that it would be easy enough to detect when temperatures are close or below freezing and turn on heating elements inside the gauge to melt any snow that it catches. For all I know this might be already happening, because the SYNOP format is not how AWS report their readings these days, and much more detailed one minute or even more frequent observations from all the sensors are being taken and transmitted back to Exeter, which may include the water equivalent of any snow that has fallen, who knows…

A bit too windy?

Figure 1

I’ve been monitoring the wind speeds from the Cairngorm SIESAWS this week where it’s been extremely windy. As you can see from the plotted observations for the last few days (fig 1), winds peaked at 15 UTC on the 15th of March, with a mean speed of 86 knots (99 mph) and gusts to 110 knots (126 mph), although mean speeds have never fallen below Beaufort force 10 in all that time. I’m beginning to think that they might have sensor problems up there at the moment, I know for the last few months reported wind speeds have been too low, but now they look like they could be too high.

There is a way to check if the wind speeds are too high though, because there is a second AWS on Cairngorm run by the Heriot-Watt Physics department (fig 2).

Figure 2

Even their sensors (the one’s that pop-up out of a can twice an hour) are also looking a bit suspect. The wind direction is definitely wrong, possibly because of a massive build up of rime in these condition. Wind speeds look too low at first, then went missing, and now look similar to the ones being reported by the Met Office SIESAWS.

Winds as severe as this are perfectly possible of course on Cairngorm, which makes it doubly difficult in deciding if they are right or wrong.

Recent high temperatures at the North Pole

Figure 1

Apparently the air temperature at the North Pole rose above freezing yesterday (25 Feb 2018). This winter, like many more before it in recent years, the temperatures in the Arctic has been exceptionally mild, at times anomalies have been more than 25°C higher than the long-term average. This is the thermograph for the North Pole up to the 23rd of February from NCEP reanalysis data (fig 1).

This is well supported by the observational data from Cape Morris Jesup, the most northerly point of mainland Greenland at 83°37″N and just 442 miles from the pole itself (fig 2). For a short while on February 25th the temperature there reached 4.7°C at 09 UTC, but by 18 UTC that evening the temperature was back down to -13.2°C.

Figure 2

This is the best aerial shot of the weather station at Cape Morris Jesup that I can find on the internet of what must be the bleakest and most isolated spot in the whole northern hemisphere (fig 3).

Figure 3 © System Operator Kim B. Svensson of the Royal Danish Air Force

It’s quite bizarre that for a while yesterday it might have been colder down here in Devon just for a few hours, than it is was in the high Arctic. It’s probably another symptom of the recent SSW event in the high atmosphere, and of course the underlying warming that’s been going on in recent years. Temperatures today across the Arctic seem to be returning closer to what constitutes normal for up there at the moment, as the milder tongue of air that caused all those record high temperatures is squeezed out by colder air (fig 4).

Figure 4 – Courtesy of EarthWindMap

Puts our 1 to 3 centimetres of snow into perspective

Figure 1

The heavy snowfalls of the last couple of days over western Russia and central Asia have put our overnight warning for of just 1 to 3 centimetres into perspective. The above chart are the reported snowfall depths at 06 UTC this morning overlaid with contoured MSLP (fig 1). As you can see from the inset table one of the observing stations close to Moscow (WMO #27612 Dolgoprudny) is reporting 53 cm of level snow (~21″). Dolgoprudny, I’m reliably informed by Wikipedia, lies 20 km north of the city of Moscow.

Russia has a terrific SYNOP observing network, but they only report a snow depth once a day, and for some strange reason, probably to do with time zones, eastern Russia report it at 03 UTC, and western Russia stations at 06 UTC. Without some kind of bespoke SYNOP snowfall application that scans all observations for the latest reported snow depth in all observation for a selected day (now there’s an idea), I can’t extend the chart any further eastward.

The mystery of the Dalwhinnie AWS solved!

Figure 1 – Courtesy of Google Maps

Thanks to some old colleagues I’ve now solved the mystery of exactly where the AWS is at Dalwhinnie. Believe it or not, it’s in the grounds of the distillery, which must be a first for the location of any weather station I would have thought (fig 1). Perhaps the Met Office could approach the likes of Glenlivet, Tomatin and other distilleries across Scotland to host a network of AWS? Then again it might end up with a disproportionate number of them being located in Morayshire, and we already have Kinloss and Lossiemouth (fig 2).

Figure 2 – Courtesy of

Looking at an aerial view of precisely where the AWS is located at Dalwhinnie, I don’t think it makes an ideal location for a climate station, being surrounded as it is by so much tarmac, buildings and warehousing (fig 3), none the less it didn’t stop it getting down to -13.5°C on the 21st of January.

Figure 3 – Courtesy of Bing Maps

The exact location of the AWS with respect to the buildings could explain some of the spikiness in the thermograph trace during the evening of the 20th (fig 4), but without an anemograph, which I don’t think it has (not that we could access the data even if it had), it’s impossible to say if the nearby buildings had anything to do with it. So it’s no wonder that Braemar on the other side of the Cairngorms, with a little more shelter, and without a distillery on the doorstep pipped it to being coldest.

Figure 4 –  Courtesy of

The other thing about distilleries is that like breweries, they can push out huge clouds of steam when they are mashing (I’m guessing at what the precise technical term is here), not that I think this would affect the sensors but if I remember it’s quite a pong!

I always had trouble getting an ice bulb going…

Figure 1 – Courtesy of Twitter

When I was an observer the biggest problem I had in winter was getting an ice bulb going when the temperature got close to freezing. Judging by the look of this Stevenson screen (fig 1) they wouldn’t be having that problem at the moment at Izaña in the Canary Islands. It’s not quite as cold as it has been recently (fig 2), but the rime seems to be building up in the northeasterly.

Figure 2

I don’t suppose they are getting very much astronomy done at the moment at the observatory, but that’s at 2,390 metres (7,841 feet) whilst Mount Teide itself rises up to 3,718 metres (12,198 ft), and is the highest point in Spain, as well as being the highest in any island of the Atlantic which of course includes us.

Looking at the very nearby upper air ascent from Guimar (WMO 60018) for midnight (fig 3).

Figure 3 – Courtesy of OpenStreetMap

it looks like Izaña is sat in an inversion with a sub-zero freezing layer that’s not quite been captured by the radiosonde ascent by the looks of it (fig 4). Although I will say at this point that my sonde application does need a good-looking at!

Figure 4

You can see from the special points that the temperature is well above freezing at the 779 hPa level, and remains above freezing till around 11,000 feet and just below the summit of Teide it goes sub-zero again (fig 5).

Figure 5

Finally to finish, here’s a satellite image from yesterday of the Canary Islands, I think you can just about pick out Tenerife with some snow cover or is that cloud (fig 6)?

Figure 6 – 2 February 2018 – courtesy of NASA Worldview.