The overnight thunderstorms

Figure 1 – Courtesy of Blitzortung

Here are a few graphics to show the extent of this early thundery spell across the country, the severity and extent of which caught both the ECMWF and the UKMO NWP models out yesterday. As far as I can see most of the lightning was from unstable medium level cloud rather than the more traditional cumulonimbus (fig 1). The rainfall from the thunderstorms looks to have been concentrated in a swathe SSW-NNE through Hampshire, where my estimates from weather radar suggest that as much as 32-40 mm fell in the wettest areas (fig 2).

Figure 2
Figure 3 – None of the rain gauges where in the right places, where was Southampton Weather Centre when you needed it?

I won’t go on about just how poor or late the warnings were for yesterdays thunderstorms from the Met Office, or just how divorced the NWP graphics used by either themselves or the BBC was from reality, the following screen shots will have to suffice (fig 4).

Figure 4 – Courtesy of the Met Office (1&2), Blitzortung (3) and the BBC (4).

When you just can’t get that yellow warning area quite right…

For as hard as the Met Office might try, they just can’t seem to get the area for today’s yellow warning of heavy rain and thunderstorms quite right. Here’s how the shape of the yellow warning area looked yesterday (fig 1).

Figure 1

And here’s how the shape looked after a belated adjustment at 0115 BST this morning, after overnight thunderstorms ran NE from the English Channel, and were a little bit more persistent than the model reckoned they’d be (fig 2).

Figure 2 – Courtesy of the Met Office

And here’s how the shape has looked since 1100 BST this morning (fig 3).

Figure 3 – Courtesy of the Met Office

But this is how it looks in reality right now (fig 4).

Figure 4

The moral of this story is whatever you do – never leave Snowdonia out of the heavy rain warning area.

Figure 5 – Courtesy of Blitzortung

As far as I can see, the best solution to the problem of continually having to update the area affected in thundery weather, would be to just slap a complete yellow alert across the entire country, for heavy rain, frequent lightning, hail and flash flooding, and be done with it (fig 6).

Figure 6

Tonight’s thunderstorms and Met Office warnings

The English Channel seems to be full of thunderstorms this evening and they are all marching steadily northward. The rainfall intensity is similar to the storms this afternoon of the Lizard, and I wonder if we could have a repeat occurrence of what happened at Coverack somewhere else along the south coast tonight?

Figure 1

The current yellow warning from the Met Office runs out at 2355 BST. Tomorrows warning for much further north doesn’t start till 0005 BST, so technically there is no warning out for around midnight – bizarre. I would have thought now would be a good time for the Chief forecaster to extend the one for the south coast, as I type this, it’s 2320 BST and they still haven’t done it – very odd. In light of the Coverack event earlier today, I thought it might be even worth them ‘upping’ the warning to amber might be in order, I say that as I listen to the Blitzortung website crackling away on my computer, and flashes every 10 seconds out of my Velux windows to the south.

Figure 2 – Courtesy of Blitzortung

 

A dollop of rain at Middle Wallop

Figure 1

There was 60 mm of rain reported in the 24 hours that ended at 06 UTC this morning from Middle Wallop in Hampshire. There were also some other nuggets of high rainfall from other parts of the country too such as the Isle of Man, Norfolk, Sussex and the southwest of Scotland (figs 1 & 2). I wonder if the advice in yesterdays yellow warning of rain from the Met Office held true for those parts of the world yesterday?

…there is a low likelihood of flooding of homes and businesses as well as to disruption to transport.

Figure 2

The total at Middle Wallop looks high, because according to the AWS the bulk of the rain seems to have fallen between 18 and 00 UTC yesterday evening when little or no weather was reported by the weather sensors (fig 3). The sensors may of course may have been unable to cope with a sudden cloud burst, and just packed in till they were reset by the morning shift. One shortcoming of any AWS is that they don’t in my experience (well the ones run by the Met Office) report ongoing thunderstorms. There’s no reason why they shouldn’t, apart from the cost of the sensor, because I’m sure that the Vaisala AWS can detect thunderstorm activity.

Figure 3

The estimated totals from the weather radar for the 18-06 UTC period interestingly do show a hot spot around Middle Wallop with a couple of yellow pixels (40-50 mm) which supports the local nature of the 60 mm total from Middle Wallop, but a much larger area of high rainfall south of the Wash and north of Marhan has fuschia coloured pixels (50-75 mm). The 18-06 UTC total from Marham was 43 mm, which I underestimated at just 32 mm (fig 4), but my mapping conversion code is far from perfect, and I may have been a pixel out (well that’s my excuse).

Figure 4 – Courtesy of the Met Office

 

Thundery rain for southeast

Figure 1 – Courtesy of the Met Office

…there is a low likelihood of flooding of homes and businesses as well as to disruption to transport.

The Met Office are quite definite about the chances of any disruption in the latest yellow warning of heavy rain they have issued for southeast England for the remainder of today and overnight, especially in light of the latest weather radar images this afternoon (fig 2).

Figure 2

The one good thing, is that the thundery showers at the moment aren’t hanging around, and are moving quite smartly N’NE ward (fig 3).

Figure 3 – Courtesy of Blitzortung

Unusual medium level shower activity…

Figure 1

I’m probably going to shoot myself in the foot with this one, but it looks to me, and I could be wrong, like much of the precipitation that’s been showing up on this afternoon’s weather radar, especially the belt that stretches across central England is from medium level unstable castellanus cloud, and is producing nothing more than the odd shower. There are some brighter echoes within, and the observing network is pretty thin so it could be falling between the gaps, but I see very few reports of any significant rain or thunderstorms from it.

Figure 2

Here’s the latest visible image (fig 3) that shows the band very well.

Figure 3

The rainfall over western Scotland looks even more dramatic, and this is thundery in nature (fig 4), although the rainfall indicated in the weather radar image looks very intense, it also seems to have escaped the observing network so far.

Figure 4 – Courtesy of Blitzortung

Interestingly, the current Met Office warning that is in force for heavy thundery rain this afternoon, completely omits the west and north of Scotland (fig 5)!

Figure 5 – Courtesy of the Met Office

 

Super cell (updated)

Figure 1

I reckon this big CB formed over Loudes in the Haute-Loire and Auvergne-Rhône-Alpes region of central southern France this afternoon.

Figure 2 – Courtesy of Blitzortung

Addendum

I was kindly sent a link to a very interesting article about this big thunderstorm, on a website specialising in reporting about severe weather in France, here are a couple of images from that article.

Figure 3 – Courtesy of Keraunos
Figure 4 – Courtesy of Keraunos

More miss than hit from the Met Office

Figure 1 – Courtesy of the Met Office

I might have agreed that the Met Office warnings for Saturday had been warranted, but the yellow warning for Sunday was a little over the top, both in the area of extent and the amount of rain that fell. Here in Devon, we had a very unspectacular 0.4 mm of rain in the 24 hours ending 06 UTC this morning, and that was true for the whole of the southwest and most places in the top half of the yellow warning area (fig 1). True, a lot of the rainfall would have come in sharp bursts because a lot of it was associated with thunderstorms, in fact Blitzortung reports a 183,593 flashes in 24 hours (fig 2), but a good part of Kent which was in the thick of the SFERIC activity, so no more than 2-4 mm of rainfall in the 24 hours in my estimates.

Figure 2 – Courtesy of Blitzortung (28 May 06 UTC to 29 May 06 UTC)

We ended up with a mainly dry day here in Devon, with just a few spots of rain in the mid afternoon, in fact until then the day had been surprisingly bright despite a shield of thick upper cloud.

Figure 3 – 28 May 06 UTC to 29 May 06 UTC rainfall estimates
Figure 4 – 28 May 06 UTC to 29 May 06 UTC reported rainfall

The only mitigating evidence that I can find, is an area of the Sussex coast around Chichester, that may well have received in excess of 40 mm of rain if my weather radar estimates (fig 5), which look a little on the high side for the convective rainfall when comparing them to reality (fig 4). I’ve looked for reports of flash flooding for yesterday, but found none on the Google searches I’ve done. So, looking at the event as a whole, it may have looked very spectacular in the southeast, but as far as can see, it was more miss than hit as far as the yellow warning was concerned.

Figure 5

Yesterday’s thunderstorms

Figure 1

Despite the number of thunderstorms across the country yesterday (fig 2), estimated rainfall totals for yesterday (06-06 UTC) were generally low (fig 1), although there were some more active thunderstorms that tracked NNW across northern England and Scotland that enhanced the totals, one notably over the southern Lakes and another one that clipped Fife.

Figure 2 – Courtesy of Blitzortung (27 May 06 UTC to 28 May 06 UTC)

Rainfall amounts from bands of thundery rain like this must be almost impossible to predict, and I think the forecast from the Met Office for yesterday was pretty good, and the warnings that they issued (fig 3) look well justified.

Figure 3 – Courtesy of the Met Office

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