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 lymington.org)

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 Cat-Cam.co.uk

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

 

Reykjavik time-lapse captures overnight snowfall

I was a bit late on this one but I saw this on the BBC this morning and thought that you might like to see it:

Reykjavik time-lapse captures overnight snowfall – http://www.bbc.co.uk/news/world-europe-39108533

March in like a lion

Figure 1 – Courtesy of Met Office

March may be about to come in like a lion, particularly in the southwest of the country, as a flat triple point low runs east along the English Channel tomorrow morning (fig 1). All looks fairly innocuous at first, but behind the trailing occlusion that the low drags in, are some very strong even gale force west northwesterly winds if the latest run of the GFS model is to be believed later in the day, and by that time colder air will have started to turn the rain from it to snow, especially over any hills in the west (fig 4).

Figure 2 – Courtesy of OGIMET

Figure 3 – Courtesy of OGIMET

Figure 4 – Courtesy of OGIMET

Why so little snow at Scottish ski resorts this season?

Figure 1 – Courtesy of WinterHighland

There are obviously two key ingredients for a good skiing season anywhere in the world, and they are:

  • Air temperatures less than 0°C for as long as possible
  • Plenty of precipitation.

The lack of snow in Scotland during this Autumn and Winter are a result not only of it being much warmer than average (fig 2), but also due to the fact that it’s been comparatively dry. In fact the last four months October to January have been the driest four-month period (October to January) since around 1976 in Eastern Scotland, with only around two-thirds of the usual amount of precipitation during that time (fig 4). In the same period last year there was over 789 mm of rain compared with just 317mm this year. Although of course much less precipitation falls at Aviemore than does over the Cairngorms, the hyetograph for Aviemore (fig 3) does illustrate just how much dry weather there has been. The lower than average rainfall is the result of more anticyclonic weather than usual, resulting in higher than average surface pressure, which translates into fewer storms and fewer active frontal systems.

Figure 2

Figure 3

Figure 4 – Data courtesy of UKMO