Admittedly rainfall accumulations this month are completely topsy turvy, and it’s still been a very dry month in many parts of Scotland, but the meteorological drought that affected many parts of the south did come to an abrupt end this week with some heavy rain, as droughts so often do. I’ve tried to wheedle out plotting totals for stations where I had more than 25% of reports missing, having said that there are still a few oddities, Rhyll being one of them, although the 6.4 mm total there is kind of supported by the 13.6 mm at nearby Hawarden.
I’ve just rejigged the code for this application, and it now uses a combination of priorities to get the most accurate result. If there’s a 24 hour 06-06 total that’s great it will use that, and many of the main UK of stations have a 100% reception rate using that value alone. If there isn’t a 24 hour total, like in Ireland and parts of Europe, I add up the available 12 hour totals (06-18 & 18-06). Finally if there are only 6 hourly totals, as in the United States I add these up. The Americans, as far as I can see, don’t report nil rainfall totals as we used to do at one time, so you have to rely on the indicator in the initial block being correct. The whole area of rainfall reporting in SYNOP from different countries is a complete nightmare to program, and I still have to write code that throws back totals to the previous day, but for now this will have to do. If you have any complaints about any of the totals, please feel free to have a go yourself.
The cold front that brought all the rain to parts of England earlier this week finally managed to penetrate the warm air over central Europe and bring thunderstorms and a sharp drop of temperature with it. The interesting thing about the 15 UTC visible satellite image (fig 1) is just how sharp an edge of the cloud the cold front had, it was either blues skies or frontal cloud, and in the image I can see at least three large embedded CB’s. The demarcation in cloud reminded me of what occurred earlier this week over southeast England. Here’s the Met Office analysis for yesterday at 12 UTC (fig 2), and as you can see there is not just one cold front but two.
Figure 2 – Courtesy of the UKMO
Here’s the plotted chart for 15 UTC yesterday for the area (fig 3) and notice that temperatures at places ahead of the cold front in eastern Germany where as high as 30°C at that time.
Here’s the observation sequence from Regensburg, Bavaria for the last 24 hours, in the space of just a few hours the temperature fell from over 30°C to around 11°C (fig 4) during the late afternoon.
Judging by the 06-18 UTC rainfall totals (fig 5) the convective activity from the CB’s didn’t produce the heaviest rainfall, that occurred further west in the frontal cloud, even though there was a lot of SFERIC activity (fig 6).
Figure 6 – Courtesy of Blitzortung
Figure 1 – Data courtesy of NCEP reanalysis
The extremely high temperature anomalies seem for the moment at least seem to have disappeared from the Arctic. This temperature anomaly chart (fig 1) is for the first 15 days of May 2017, and yes anomalies are still mainly positive in the Arctic, but in a range -2°C to +6°C, rather than in excess of +16°C that they were back in January and February. That might explain why Arctic sea ice has staged a bit of a recovery during late spring. There are a number of anomalous cold areas, one north of the Great lakes in Canada (-4°C) and another one over Scandinavia and northeast Russia (-6°C), the latter causing problems with heavy late spring snowfalls in places. Central North America, Greenland and large parts of central Asia have seen a very warm spring with anomalies typically +4°C above the 1948-2014 long-term average.
Figure 1 – From radar images courtesy of the Met Office
Yesterdays estimated rainfall totals from the weather radar [06-06] showed a wide band of 8-24 mm totals, with an inner central core of 24-32 mm, and small areas of lime green pixels indicating areas in excess of 32 mm particularly in Hampshire (fig 1). Southern Lincolnshire seemed to be wettest from the 24 hour totals in the SYNOP reports (fig 2), with Holbeach reporting 36.2 mm, which I didn’t pick up from the rainfall radar which is surprising as it did much better further south, perhaps the Chenies spiking affected the averaging algorithm, either that or it was the flux capacitor.
Yesterday’s rain will certainly have freshened things up in the southeast, and might even have put a stop to all the talk of drought, but if it hasn’t, then the rain from tonight’s low might well do the trick, as it tracks by just to the east (fig 3).
Figure 3 – Courtesy of the Met Office
I was saving this article for later in the month because I thought that judging from the first ten days of May it might end up being record dry affair this year, but now, as we are approaching mid-month, and looking at the latest NWP mid-range forecasts, it looks like the second half of May will be rather cool, cyclonic and showery across the country, with any drier and warmer spells mainly confined to the southeast.
No real consensus on one particular dry year for all regions, although May 1991 was the driest in four out of the ten regions, mostly in western and central areas (fig 1).
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).
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 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.
The first eight days of May carry on in much the same vein as April left off, and that’s predominately dry. Large parts of Scotland, Ireland and the northern half of England have yet to see any rain so far this month (fig 1). There’s been a little more rain in the south, especially in the southwest and the northwest of France (fig 2).
At one point last month, I thought the rain gauge at the Gogarbank AWS (close to Edinburgh Airport) was malfunctioning, but I’ve heard a number of people quote rainfall totals for it, so I think that it’s working fine but the area around it is just transforming into some kind of arid semi-desert, with tumbleweed blowing across the enclosure. The hyetograph accumulations show a total of 149.4 mm since the start of the year (fig 3) if I’ve got my figures right, which is not a lot for the east coast of Scotland, and the bar chart resembles a series of diminishing returns as far as daily totals are concerned.