Snow refers to forms of ice crystals that precipitate from the atmosphere (usually from clouds) and undergo changes on the Earth’s surface.[2] It pertains to frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away. Snowstorms organize and develop by feeding on sources of atmospheric moisture and cold air. Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, which freeze in hexagonal-shaped crystals. Snowflakes take on a variety of shapes, basic among these are platelets, needles, columns and rime. As snow accumulates into a snowpack, it may blow into drifts. Over time, accumulated snow metamorphoses, by sintering, sublimation and freeze-thaw. Where the climate is cold enough for year-to-year accumulation, a glacier may form. Otherwise, snow typically melts seasonally, causing runoff into streams and rivers and recharging groundwater (info courtesy of Wikipedia).

Winter drawers on up the Zugspitze

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.

Figure 2

BBC: Ben Nevis snow free for first time in 11 years

Figure 1 – Courtesy of the BBC

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.

Figure 2 – Courtesy of the backcorries blog

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.

Figure 3

The rainfall anomalies for the period between November 2016 and March 2017 were generally near average, with November being a dry month (fig 4).

Figure 4 – November 2016 – March 2015 rainfall anomalies – Courtesy of the Met Office

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).

Figure 5 – November 2016 – March 2015 temperature anomalies – Courtesy of the Met Office

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.

Steep decline in snowfall since 1931 in Central England

Figure 1 – Original UKP and CET data courtesy of the Met Office.

I reckon that there has been an almost 60% decline in annual snowfall since 1931. This won’t surprise a lot of people, because snow has become something of a scarce commodity in recent Winters, especially the further south that you are. Before I go any further the science behind this article is a bit thin, it’s based on a mix of daily Central England Temperatures [CET] and daily UKP rainfall (central region), but what the hell, you’ve got to start from somewhere, and I don’t think the Met office would have provided me with the required climate data to do this for free.

The biggest fudge factor, and don’t forget that even the most sophisticated and complicated NWP software employ some kind of fudge, is the algorithm that takes a daily maximum and minimum temperature, and decides if there’s any precipitation reported for that day, what likely probability is that it would fall as snow and accumulate. This is obviously easy if the maximum temperature for the day in question was below freezing, but not so easy say if the maximum is +5°C and the minimum is -1°C, so all you can do is give it your best guess. I suppose you could also look up the LWT for that day, and maybe get some kind of idea of what kind of air mass the country is under, but I didn’t go that far, and kept it as simple as possible.

Getting back to the chart (fig 1), you will see that my trusty algorithm has identified the snowiest winter in the last 86 years as being that of 1946-47, so that’s a good start. The second snowiest season it reckons was 1978-79, and having experienced of winters since the early 1960’s in various parts of the country I wouldn’t disagree with that. I guess that the accumulated snowfall for that season, ignoring melting of course, was close to a 100 cm, with 1946-47 producing an accumulation of just over 140 cm. I entitled the first article that I wrote about using daily CET and UKP to estimate a snow depth; ‘Central England Snowfall’; in fact it’s probably more appropriate to imagine the value as an index rather than a specific depth of snow. There have been some years with no snowfall when the algorithm couldn’t detect any snow, these were for the years 1988-89, 2013-14 and 2016-17, perhaps the code I calculate the daily probabilities requires a bit of tweaking, but then again, the last snow that I can remember settling down here in our part of Devon, was way back in 2010.

I did the original work for the application, which I call Central England Snowfall, about ten years ago now, but after deciding to give the code a bit of a spring clean today, I thought that I’d write an article around it. It’s a bit of fun because the science that I use could be regarded as suspect, but as far as I know, there are no long-term graphs available on the internet for annual snowfall totals for any climate station in the UK. If you do find one, or perhaps know of a graph than spans 60 years or more please let me know, because I would be very interested to see it, and would certainly include it in this article. I do have some evidence though, in the shape of daily climate records courtesy of Alistair McClean, Curator of Natural Science at the Weston Park Museum in Sheffield, for the period 1950-2010, which luckily includes daily values of fresh snow and snow depth. As you can see in this shorter period (fig 2), annual totals on the linear trend have also declined, by almost 40% in the last sixty years. The graphs are quite similar, even the estimate of snowfall that I make for the winter of 1978-79 are reasonably close (actual 116 cm estimated 98 cm). Having experienced that winter firsthand in the higher suburbs of that city though, I would say that the reported values maybe rather on the low side.

Figure 2 – Data courtesy of Weston Park Museum, Sheffield

It’s a great shame that the Met Office stopped producing the Snow Survey of Great Britain in 1991, if that information could be digitised and collated it would make a wonderful climate resource for snowfall in the UK. Finally, I would just like to give a special mention to the website of Dr Richard Wild and is thesis ‘Spatial and Temporal Analysis of Heavy Snowfalls across Great Britain between the years 1861-1999‘, a fascinating read for the snow lovers amongst us.

If this wasn’t a polar low the next one could be…

Figure 1

The small low pressure in the Moray Firth at the moment (fig 1) doesn’t quite fit the bill as a classic polar low according to my old copy of the Meteorological Glossary. It describes a polar-air depression as:

A SECONDARY DEPRESSION of a non-frontal character which forms, more especially in winter, within an apparently homogeneous polar AIR MASS; near the British Isles the development is usually within a northerly or north-westerly airstream. The chief characteristics of this type of depression, which seldom becomes intense, are a movement in accordance with the direction of the general current in which the depression forms, and the development of a belt of precipitation near the depression centre and along a trough line which often forms on the side farther from the parent depression where also the pressure gradient (and surface winds) is increased.

Meteorological Glossary (6th edition 1991) Courtesy of the Met Office ©Crown Copyright

In this morning’s visible satellite image (fig 2) the trough, which the Met Office have as a wrap round occlusion in their midnight analysis, would usually occur on the western side of the low in this situation, or so says the glossary, but not with this feature looking at the imagery and the weather radar (fig 3).

Figure 2

Figure 3

The precipitation is of snow across the north of Scotland down to quite low levels this morning, and warnings have been issued by the Met Office (fig 3). I hadn’t notice that the Met Office had finally updated the dreadful mapping that they use in their warnings, a lot smarter, but about time.

Figure 4 – Courtesy of the Met Office

Although this low might not be classed as a classic polar low, a proper one might be developing off the coast of eastern Iceland, because the latest pressure falls at Torshavn (fig 5), indicate either a trough or maybe even a proper polar low might be squeezing itself into the tight northerly flow and head southward later today (fig 6), so you never know.

Figure 5 (the wind directions maybe spurious at times)

Figure 6 – Courtesy of OGIMET

Sign of things to come at Baltasound

The cold air has dug back in behind the cold front at Baltasound, turning the rain to snow, as the low pressure whizzes across the Northern Isles.

I wish someone would sort out that anemometer at Torshavn, I’m sure that the wind direction is the exact reciprocal of what it should be, it’s happened before, you just can’t trust those AWS.


Late April cold spells and the Easter Snowstorm of 1908

Figure 1 – Lymington High Street – April 25th 1908 (courtesy of

Easter in 1908 fell late, so the snow that fell over much of southern England must have come as a big surprise on the Easter Sunday on the 19th of April (fig 1). The following week was intensely cold for late April, and there were periods of heavy snow across much of southern England. In an article in the Met Mag of May 1908, Fred J Brodie said this about the snow at Oxford:

The conditions at Oxford are interesting in a special degree on account of the length of the meteorological records at the Radcliffe Observatory which run from 1853. The depth of snow there was 17 inches, and the only instance of a greater amount being recorded at any time of year was on February 13th and 14th, 1888, when 24 inches of undrifted snow was measured.

I love the comment that Fred went onto make a few lines further on…

The practice of comparing, for the purpose of record making, observations made in two different localities is not to
be commended…

He of course is completely right in what he says, but he must be spinning in his grave these days, on the goings on in the early 21st century with extreme temperature records I would have thought, because no one, and that includes myself seems to give a hoot these days about comparing extremes from weather stations without knowing thinking much about their actual location. You can find an article about the events of April 1908 on the Weather Outlook forum, which includes details of snow depths recorded at the time, plus a lot of other information and photographs about the blizzard. The Weather Magazine of December 1981 also had an article about April 1908 in which it linked it to the April of 1981 and said:

The marked similarity of the graphs for 1908 and 1981, especially in the second half of each, is confirmed by a correlation coefficient of 0.93 for the last 15 days of the month. For the full month the correlation coefficient is 0.65. The weather of late April was remarkably similar in these years.

Since 1981, the daily CET series may well have undergone some slight modifications, but there is most definitely a cold spell that occurred during at the second half of each month, the minimum CET in 1908 was a couple of degrees colder than it was in 1981 though, and those on the 24th and 25th still hold the record for lowest minimums on those two days (blue stars). Personally I only see a broad similarity between the two, I’ll have to spend some time and write some code to generate a correlation coefficients between these two months and see what I come up with. If you look closely at the graph of CET (fig 2), you’ll notice that in just over a week, maximum anomalies rose from around -8°C to +8°C. The resultant rapid thawing of lying snow from the week-long cold spell lead to great flooding in places along rivers in the southeast especially the Thames, and the Great Ouse at Buckingham.

Figure 2

Synoptically, the 25th of April in both 1908 and 1981 were slightly similar in that they were both cyclonic in nature.

Figure 3 – Courtesy of NCEP/NOAA reanalysis

But up aloft in the atmosphere the cold air of 1908 was much deeper than it was in 1981 (figs 4 & 5).

It seems cold outbreaks towards the end of April are not at all uncommon, I’ve just picked on probably two of the more extreme events. Next week promises its own cold outbreak (fig 6), but synoptically, if the GFS model is correct, it will be more of a cold northerly rather than cyclonic as it was either in 1908 or 1981.

Figure 6 – Courtesy of OGIMET


April snow for Cairngorms

Figure 1 – Cairngorm from Loch Morlich courtesy of © Winterhighland Limited

It’s proving to be a cold and showery Easter over Northern Scotland this year, and the showers affecting the area on Saturday afternoon look like they are putting snow down to ~3000 feet if this webcam image is anything to go by (fig 1). That’s because the cold air over Scotland is holding the air temperature on Cairngorm at a very cold -2.9°C (13 UTC) at the moment. The heatmap of air temperatures on the summit since the start of March shows that until this last week, it had been relatively mild since around the 24th of March (fig 2). It looks like the high ground might get a bit more snow overnight, but it might be a bit late to extend the skiing season from what I can see from the other webcams in the area.

Figure 2

At the same time it’s been quite a benign Spring as far as gales and storm force winds are concerned on the summit (fig 3).

Figure 3

29-30 March 1952 – Heavy snow and blizzards in the south

Figure 1 – Courtesy of the Met Office and © Crown Copyright

On the 29th and 30th of March 1952  a cold, strong easterly airflow affected the southern half of England with a period of heavy snow. According to the Weather log of the RMS snow varied from 3 to 6 inches and reached 10 inches at Northolt. The squally winds, which gusted to 60 mph, blocked 330 main roads across the south, with deep drifts. In places the temperature on the 29th remained below freezing all day, and the snowstorm was probably the worst to affect southern England in late March since 1916.

The Monthly Weather Report from the Met Office says about the weather at the end of March 1952:

Snow fell widely from the 27th onwards, notably in southern and Midland districts of England. On the 29th there was severe drifting. Snow was reported several inches deep in places in Scotland, while over a large part of southern England, depths of from 3 to 8 inches, with drifts in places of up to 6 feet, were reported on the morning of the 30th.

Figure 2 – Courtesy of Wetterzentrale

It may have been cold over the British Isles but the real cold air remained further east, but the easterly flow was enough to cause the country some real problems even though it was early Spring.

Figure 3 – Courtesy of Wetterzentrale

Here’s an earlier plotted chart that I found for Saturday night at 00 UTC. It’s from a great little book published by the Meteorological Office in 1956 called ‘Weather Map’, and which you can now download as a PDF from their library. It’s a shame that I didn’t realise this when I bought a second-hand version of it from Abe books earlier this year!

Figure 4 –  Courtesy of the Met Office and © Crown Copyright

14 March – Classic nor’easter

Figure 1

Truly horrendous weather in northeast United States today, the low which has rapidly deepened through the day is now just east of New York. The highlighted observation (fig 1) is Mount Washington.

Figure 2

I think we’ve all seen this scenario a few times in the past across the eastern United States. The rain will probably turn to a few hours of snow before it dies out in more southern states, but north of Atlantic city it looks like it could put down a lot of snow before it’s done.

Hill snow and strong winds

Figure 1 – Courtesy of

There has been a fair bit of hill snow above 300 metres across North Wales and the Pennines so far today (fig 1), I also notice that the Met Office have just issued a yellow wind alert in the southwest of England for this afternoon (fig 2), all in all, a cold and cyclonic early March Sunday.

Figure 2 – Courtesy of the Met Office

Figure 3 – Highest gusts 12 UTC

Figure 4 – Plotted 12 UTC chart