Yesterday – 18 May 2017

Apart from the area of rain that affected the east of the country,  the other interesting thing in this estimated accumulations chart as far I’m concerned here in the southwest, were a band of showers that started life around Falmouth, and ran ENE across south Devon and into Dorset during the day. The trajectory of those showers was diametrically opposed to that of the rainband in the east which was moving due north, later in the evening the remnants of the showers curved to the right and took a course that was more SE’ly. I notice that already today, there’s a large CB and associated heavy shower coming onto the north coast of Cornwall in the NW’ly flow.

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

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

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

Interesting trajectory

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.

Figure 1

Rainfall restricted to far southwest

Saturday, 6th May 2017

Yesterdays rainfall never made it much further north than Plymouth, so most of Devon got away with a dry day, with some brighter intervals during the afternoon period. The wettest place yesterday was the Lizard, although my weather radar estimates didn’t quite capture the 9.8 mm 06-06 total from St Mary’s.

A wet day in Devon…

I said that we needed some rain, but never thought that we would end up with as much as 36.8 mm in the last 24 hours, as was the case at nearby Dunkeswell. The light blue area (16-24 mm) in the following composite 24 hour total, almost maps out the county of Devonshire as if it was meant just for us…

Figure 1 – Images courtesy of the Met Office

For over five years now I’ve been adding the values from individual coloured pixels in weather radar images to create a composite total, one or two people pooh poohed the idea, it wasn’t an original idea the radar team generated them but never made them available, but it’s something that I’d always wanted to do ever since I’d started working in the Nimbus visualisation team at the Met Office, but was never allowed to do, so when my application gets its estimate spot on as it’s done in this case, I do tend to end up crowing about it a bit. As you can see from the inset hyetograph I estimated 35.7 mm at Exeter (fig 1) but the 06-06 UTC total in actuality it ended up as 34.6 mm (fig 2).

Figure 2

This will have put an end to any absolute or partial drought that had been going on in the south, or come to that any dry spell (15 consecutive days <1.0 mm on any day) that had been lurking about. At least now all the water butts in Devon have been refilled and the House Martins will have some mud to collect.