I thought that I would investigate and find out exactly what climatologically is the sunniest month of the year using monthly sunshine data from the Met Office. The gridded sunshine record only started in 1929, but I’ve been reliably informed by someone in the know at the Met Office, that plans are well advanced to extend this (along with the rainfall and temperature series), back to at least the start of the 20th century, which I applaud, although in my opinion it’s a long way overdue. The add-on to my application looks not only at sunshine, but rainfall and temperature too, and for any region within the United Kingdom. The pie chart I’ve include is for England & Wales (fig 1), and reveals, surprisingly to many I bet, that May is climatologically the sunniest month of the year in 35.2% of years since 1929, followed by June in 31.8% of years, and July in 19.3% of years.
Figure 1 – Data courtesy of the Met office
Also rather surprisingly, it can happen that in some years April is the sunniest month. According to my application that’s occurred five times, in 1945, 1954, 2002, 2007 and 2011, so three times in the last 15 years. There’s always a chance that I’ve made an error let me know if I have.
The sunniest month in the entire England and Wales record was the July of 2006 with 287.6 hours of sunshine (fig 2). The sunniest month in the famous summer of 1976 was also a July with 251.5 hours of sunshine, but ranked only 13th in the list of sunniest months in a year.
Figure 2 – Data courtesy of the Met Office
What was the sunniest May in the UK? That of course depends on where you live, so using the regional gridded sunshine data series from the Met Office that started in 1929 here is a map of the sunniest May for each of the nine individual regions, and for the whole series in a horizontal bar chart (fig 1). May is climatologically the sunniest month of the year in the UK, but more of that in an upcoming post, and by the look of it, the May of 1989 was the sunniest in nine of the seventeen regions, including the UK and England and Wales, if the gridded sunshine values are anything to by.
Figure 1 – Data and map courtesy of the Met Office.
The 1989 record certainly is in no danger of being broken in the southeast this year, but it’s certainly could in Northern Ireland and the west of Scotland, where they’ve got off to a flying start (fig 2).
The pressure has fallen surreptitiously and steadily over the last few days here in the southwest, from around 1028 to 992 hPa without most of the population probably even noticing, unless of course they still have a hall barometer that they tap before going out to work, but that’s my very old-fashioned 1950’s suburban view of the world, that’s all but gone in these days of smartphones and tablets.
That fall of pressure and the recent dry spell, got me thinking about the obvious close correlation that exists between air pressure and precipitation, so I thought that I would overly the pressure and precipitation in a single graph, and hey presto a new graph, which I call a baro-hyetograph for want of a better word, is born. The top baro-hyetograph is for the period since the start of the year for Exeter airport, and shows the recent dry spells and anticyclonic periods very well (fig 1). The second baro-hyetograph is for Heathrow airport and paints a very similar picture (fig 2).
The interesting curved trajectory that the showery rain took overnight left most of Devon reasonably dry (fig 1), although we might not be so lucky today. The rain must have come as a shock to some northwestern areas, and today’s cloud puts an end to an eleven day spell of sunny days.
Many places across the British Isles, especially over Northern Ireland and Scotland are still without rain this month, as the dry spell that started in late March continues.
Looking at guidance from the latest NWP generated from the GFS model shows that the weather is now on the change, with a more cyclonic southwesterly spell for this weekend and the early part of next week, before high pressure rebuilds in the mid Atlantic by the end of next week. In fact the forecast for next Monday (fig 2) looks quite windy and wet, especially across the west, although the southeast does look like it will escape the worst of the rain.
Figure 2 – Courtesy of OGIMET
Having said that, the Met Office in their forecast charts for Sunday night don’t develop this feature quite so deeply (fig 3).
Figure 3 – Courtesy of the Met Office
It’s been a wonderfully sunny start to May in Northern Ireland, with Aldergrove recording 133.3 hours of sunshine in the first 10 days of the month. They have now jumped ahead of the ‘Sunshine Island’ of Tiree as the sunniest place in western Europe this month, with Alicante now close behind in fifth position (fig 1). In stark contrast, the dearth of sunshine in the southeast is quite noticeable in the chart, with just a measly 33.7 hours of sunshine so far this month at Wattisham.
I was looking at the graph of rolling 365 day rainfall totals for the southeast region (from UKP data that I download from the Met Office) the other day, as you do, and noticed a tentative seven-year cycle from around 1970. I’ve read about a possible seven-year cycle in Winter temperatures, but never heard mention of one for rainfall. It’s not that clear to see, and I can’t back it up with any statistical evidence, but if you squint your eyes just a little bit everything does seem to fit quite nicely!
The one thing I can say with a lot more confidence, is that the last 365 days rainfall accumulation (up to the 30th of April 2017) in the southeast added up to around 595 mm, which is about 80.6% of the long-term average for the region, and it’s the lowest 12 month rolling total since 2012. If there is any sort of seven cycle, and the last dry cycle occurred around about 2011, the next dry cycle should occur in 2018 or thereabouts.
The one other interesting that struck me about this graph, was how the dry spell of 1975-1976 sits between two quite wet peaks, that fell just before and just after 1976, not a lot of people know that.
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.
Figure 1 – The AWS at Tiree courtesy of the Met Office & Ordnance Survey
Tiree is the place to go if you want to top up your tan this month (fig 2). In the first eight days they’ve already got a ton up with 113.2 hours of sunshine, which is a daily average of 14.1 hours, and almost 90% of the maximum possible. Yesterday at Tiree, they cracked the 15 hours of sunshine in a single day mark, and will no doubt do it again today.
Not far behind them are the two sunshine stations in Northern Ireland, followed by Prestwick on the Ayrshire coast (fig 3). I find it amazing how nature always tries to redress the balance in these things, after such a cloudy month in this part of the world last month.
To put it into perspective, the sunshine totals so far this month in Western Scotland are higher than anywhere I can see in the western Mediterranean, with Alicante the only station to have recorded more than 100 hours this month (fig 4). Having said that the potential daily sunshine is higher the further north you go at this time of year, which does help a bit.
***Updated 10th May 2017 ***
Due to the unprecedented numbers that have been looking at this article, I thought that any new readers would like to see if Tiree did actually get 15 hours of sunshine yesterday, not quite they got 13.7 hours, nevertheless there are still currently the sunniest place this month in Western Europe with 126.9 hours of sunshine in just nine days (fig 5), that’s an average of 14.1 hours per day. Sadly today, there are cloudy skies over Tiree, but it was good while it lasted.
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.