Drought, what drought

Figure 1

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.

19 May – cold front drops temperatures sharply across Germany

Figure 1

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.

Figure 3

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.

Figure 4

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 5

Figure 6 – Courtesy of Blitzortung

 

17 May debrief

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.

Figure 2

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

Driest ten months in 100 years recorded in southern England [updated]

According to the New Scientist the last 10 months were the driest July to April for southern England in records stretching back more than 100 years, or so say the Centre for Ecology and Hydrology, which I must say is the first time that I’ve ever heard of them.

Possible discrepancy in latest July to April total

When I first read this I didn’t quite believe the claim that this arbitrary 10 month period between July 2016 and April 2017 had been the driest since 1910. I could remember the dry spell of 1976, and thought that this current dry spell couldn’t match it. I’ve now added code to my Met Office 1910 climate application, which I assumed used the same Met Office 1910 gridded rainfall data, so that I could graph any user defined period that I chose, and here are the results (fig 2).

Figure 2

As you can see 1976 was the driest July to April period since 1910, as I suspected it was, and there were four other years drier than 2016-17. So I went back to the CEH site and dug out the PDF of this April’s hydrological summary. I would include the relevant table from the summary in this article but I may well end up in prison if I did so because of the copyright clauses in it, suffice it to say they get a total of 446 mm for this period which I calculate 454.7 mm. Even if you look at the rainfall data for the ‘southern’ region, 1976 is still the driest period since 1910 for July-April rainfall and the latest total, 489.4 mm still don’t tally (fig 3).

Figure 3

Likely reason for the discrepancy

From reading the Hydrological summary, I assume that the Met office use the same gridded data set to create bespoke monthly rainfall totals for most of the regional water companies around the country, and one of them is Southern Water. I guess that the ‘southern‘ in the table of the Hydrological summary doesn’t exactly equate to the Met Office’s ‘southeast and central southern England‘ (fig 5) that they produce for their 1910 monthly climate series, in fact looking at the map from the Southern Water website (fig 4) it could be a combined area that includes Southeast Water.

Figure 4 – Courtesy of Southern Water

Figure 5 – Courtesy of the Met Office

So the difference in ‘catchment areas’ so to speak undoubtedly explains the small difference in totals that I found. But creating bespoke areas is confusing, the 1910 series that you can freely download from the Met Office includes 17 regions, some of which overlap and combine sub-regions, which makes it difficult to decide which area the climate data is for.

There is one thing that I have learnt from writing this article, and that is what an interesting website the CEH have, and what an invaluable publication the Hydrological summary is. Now why can’t the Met Office publish something similar in PDF format which they could email out to subscribers that’s full of climate data, perhaps they could call it the Monthly Weather Report?

Rainfall still flirting with southeast

The bulk of the heavier rain is still west of London and flirting with the far southeast again like it did yesterday. The main rainfall band is sprawled across central southern England and towards Lincolnshire, where it’s a thoroughly wet and miserable day with some heavier rain now starting to show its hand (fig 1).

Figure 1

Estimates from the weather radar indicate that Portland was the wettest station from 06 UTC with 20.8 mm, and by the looks of this mornings totals from the SYNOPs I wasn’t far out (fig 2).

Figure 2

I thought that the Met Office had now fixed the ‘spiking’ that they got from the Chenies radar (fig 1), but it looks like the tall trees there are still causing problems. Using the position of each of the six spokes that radiate west from the radar site, you could probably map the position of each of the offending trees. After extensive digging on the Internet I couldn’t locate any of the information regarding the tree’s at Chenies that I used in an article a couple of years ago, but this image from the lane that runs past the site gives you a better picture of the problem courtesy of Google street view (fig 3).

Figure 3 – Courtesy of Google Street View

In the aerial view I can now see why the tree’s are such a problem for the Met Office and how they affect the radar signal when they are in leaf (fig 4), and by means of the same image I can also see why they’ll never be removed. The problem lies in a large ‘stately’ home which lies almost due west of the radar. By the look of it is the original house that RAF Chenies was first built around in the 1930’s, and may have served as the admin offices and quarters for officers, but apart from the radar tower, a large aerial and a few other buildings associated with the 1950’s listening post, the rest of the RAF station has been demolished. The house remains though, and sits in a prime location in an isolated spot in the Chilterns, looking very well maintained and very expensive (fig 4). Interestingly, it’s the only time when I’ve ever used street view that I’ve found that I can’t drag the marker to where I can gain a view of this house. Try it yourself, drop the little man and it will take you back to the gates of the radar site. Be warned each time you do it a little red light will flash at Google HQ and all your personal details will be entered into a report at GCHQ. Maybe I’ve stumbled on Theresa May’s house and I don’t mean Chequers? It’s amazing what you can learn in an article ostensibly about weather radar in my blog.

 

May 17 briefing

Just what the Doctor ordered

Not only did the southeast get the warmest day yesterday (which is more that can be said down here in the southwest) they also got a good long spell of moderate rain, which must have come as welcome relief to the farms and gardens that have been crying out for it over the last six weeks or so. For a long time I thought that the rain gauge of the AWS in St James Park must have been faulty or perhaps full of pigeon excrement.

Figure 1

The estimates that I make from radar images were a little high, for example I estimated a 18-06 total for Wattisham of 21.8 mm and in reality they recorded 20.2 mm [06-06]. The coast of Kent seems to have escaped most of yesterday’s rain though.

Figure 2

Wattisham, as well as being the wettest place yesterday with 20.2 mm in the reported SYNOP’s (fig 3), also managed second warmest with 25.2°C (fig 4).

Figure 3

I still suspect that there is some kind of geothermal energy going on in close proximity to the Stevenson screen at Broadness, because yet again they were the warmest station in WMO block #03.

Figure 4

Despite the warmth in the southeast, I reckon the best day yesterday was in the far north or west albeit considerably fresher, Kirkwall reported 12.6 hours of sunshine, and stations in Ireland added more sunshine to their already high totals so far for May (fig 5).

Figure 5

16 May briefing

24 hour rainfall

As often happens, Capel Curig was the wettest place, with 65.2 mm in the last 24 hours (06-06) from the available rainfall reports (fig 1). I’m glad that I am not on holiday under canvas in Snowdonia this week. I do wish Met Éireann would report 24 hour precipitation totals in their SYNOPs. Not a great deal of rain for many central and eastern areas though, perhaps tomorrow will change all that.

Figure 1

The estimates from 24 hours of 5 minute weather radar images show the wettest areas being the mountains of the Lake District with totals in excess of 100 mm (fig 2).

Figure 2

Overnight Minimums

A very mild night for mid May across many parts, with Kinloss and Hawarden reporting minimums no lower than 15.8°C (fig 3).

Figure 3

Wet in the Lake District

Not a great day to be stuck in a caravan in Keswick today, with the rain drumming down on the roof, where I estimate there has been around 15 mm of rainfall between 06 and 18 UTC, but on the surrounding fells totals are already well in excess of 50 mm as they are in other parts of southwest Scotland and northwest Wales.

Figure 1 – Estimated Rainfall Totals

I would love to see just how full the River Derwent at Seathwaite looks this evening, it certainly will be a little fuller than it was earlier this month.

Figure 2 – © North News & Pictures Ltd

A few minutes later…

An even better ‘before and after’ picture of the River Derwent courtesy of Paul Kingston and Twitter.

Figure 3 – Courtesy of Paul Kingston and Twitter

The driest May’s since 1910 regionally

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).

Figure 1

15 May briefing

Western Ireland saw the heaviest rain overnight, more specifically the higher ground of counties Kerry, Mayo and Donegal seeing accumulations of more than 75 mm (fig 1).

Figure 1 – Estimated rainfall totals from Weather Radar Images

Rain is holding the temperatures down in the southeast, but I notice that there’s much warmer air just across the Channel (fig 2) at 09 UTC.

Figure 2

There was a little bit of rain overnight in the southeast but not nearly enough, but the cold front will drag its heels this week though, and could take till Thursday to clear the southeast, and if the GFS model is correct, will produce a wet day on Wednesday across the south (fig 3).

Figure 3 – Courtesy of OGIMET