I knew that I was tempting fate by publishing a story the other day about the total number of frosts in the last year and saying that we wouldn’t be seeing anymore. Well last night there was a widespread ground frost (fig 3) and touch of air frost across the country (fig 2), and I’m still busy trying to get what’s left of the egg of my face as I type. I’m in good company though, because David Braine always seems to forget just how cold it can get at Exeter airport (-0.5°C). The 10th of May is not particularly late for an air frost in the UK, but I bet gardeners on chalky soils in Oxfordshire aren’t too pleased this morning, if the -2.8°C at Benson is anything to go by.
Now that May is with us and there can’t be many more frosts to come, I thought that I’d look back at the total number of frosts in the period from the 1st of July last year and see how the seasons panned out in regard to air frosts, ground frosts and the number of ice days (maximum temperatures below <0°C for 24 hours). As always with data like this it does depend on receiving 06 & 18 UTC SYNOP data from all stations, and which you can never entirely guarantee that you’ll get, so some of these figures may not be quite exact. I also apologise for the cluttered numbers at this zoom level, which only some fancy decluttering routine would fix. You’ll have to take my word for it, the application is much better than the screenshot.
I think the number of days with an air or ground frost were significantly boosted in the southeast of England as a result of the cold spell in January. It looks like St Mary’s on the Isles of Scilly even managed to escape a ground frost during this last winter, I’m not sure about the two sites on the coast of northern France though.
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
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.
Synoptically, the 25th of April in both 1908 and 1981 were slightly similar in that they were both cyclonic in nature.
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.
Another touch of frost in places overnight, with air temperatures down to -1.8°C across the southeast of England this morning (fig 2). There has been a more general and sharp ground frost across most of the southern and eastern England too (fig 1), which won’t have please a lot of gardeners.
In fact the cold air at the moment is quite widespread across much of northern Europe and eastern Russia (fig 3), nothing exceptional, but because it comes after another relatively mild Winter and Spring so far, it’s come as a bit of a shock to some. And remember – ne’er cast a clout till May be out.
Not a perfect radiation night across Scotland, there was always a little too much residual gradient left over from yesterday, even with a high pressure cell sat right slap bang over the country. Despite this Tulloch Bridge still recorded an overnight minimum of -5.7°C [06-06] which is not bad going for mid April (fig 2).
Another lovely sunny morning down here in Devon again this morning – the third in a row (fig 1). Not wishing to rub it in at all after David Braine’s warnings of a cloudier Thursday down here for yesterday, I noticed that Exeter airport was the sunniest spot in the whole country with 12.6 hours of sunshine, ~94.6% of the maximum (fig 2). We must be in top gear making up for the dull March we had.
Last night was clear and starry, and led to a very cold night with a minimum of 0.0°C at the airport (fig 3), I wonder if he forecast that?
I suppose this is not at all surprising when you’re sat under a large anticyclone like we are at present, and as it pulls away later today we will find warmer air pushing up from France for the weekend. So we could end up with a run of five sunny days before it’s all swept away early next week.
A lovely sunny morning down here in Devon after a sharp overnight frost, the 18-06 minimum at Exeter Airport was -3.4°C. But I notice that the edge of the SC sheet has just taken Yeovilton out, and a few bits of cloud have appeared on the eastern horizon as I type, so the sunshine might not last the morning out. The SC sheet itself looks very uniform across the country, with a base of 3,000 feet and tops of around 5,000 feet if the Herstmonceux midnight ascent is anything to go by.
Another low, not all that dissimilar to yesterday’s low, is now tracking into central France with some very strong winds on its southern flank. Yesterday’s low is now sitting over the Western Isles of Scotland, meanwhile a short-lived col over central southern England has allowed a touch of frost to develop.
Because of the anticyclonic nature of this meteorological Winter with 58 days of it gone so far, the air frost count across the British isles is looking fairly respectable as you can see from figure 1. There is certainly a cold pole in central southern England due to the frosts of the last week, but there are still a number of stations holding out at zero air frosts so far this Winter.
An interesting chart plotting the total number of ice days (fig 2) across Europe so far this Winter, so if you think you that we’ve had a few hard frosts or even the odd ice day in the last week or so, have a look at further east and think again.
Of course, before someone points this out to me, ice days are when the temperature fails to rise above freezing over a 24 hour period, usually from 0900 to 0900. This chart is a count of days when the 06-18 maximum is less than 0°C, that’s because not all countries (including the UK & Ireland) report a 18-06 maximum along with their 18-06 minimum in their SYNOP reports, or an 06-18 minimum to accompany the 06-18 maximum come to that, so this will have to do. I won’t even bother trying to sort out the time zone issues a chart like this one (fig 2) that spans multiple time zones throws up.
Interestingly the French do report both a 12 hour maximum and a minimum in both their 06 and 18 UTC SYNOP observations, which is very sensible, they also report hourly rainfall totals which again I applaud them for, but I still won’t buy any French apples, not after they sank the Rainbow Warrior in 1985!