Evening thunder

A couple of brief thunderstorm downpours on Saturday evening is the only rain I've had since the 11th May. The outlook does have somewhat mixed fortunes though, in fact my area could be a bit cooler than many in some coming days. Temps still at least average even on the less good days though.

You were right, and I could see the cells that formed near Swansea later, they looked quite good. I went on a little chase yesterday, got under a small torrential shower, then afterwards stopped and heard 3 rumbles from a new cell near Launceston. Apart from that not a lot. Convection seemed to struggle and any cells were unimpressive looking and fell apart quickly. Ah well. I'm not confident about today for me unless anything elevated can happen. The Met Office keep mentioning the risk thunderstorms/thundery showers every day though even if it looks less likely here. A few years ago they seemed reluctant to use the word 'thunderstorm', now if anything it's the opposite.

Hmm.. I feel that low cloud inland is causing the surface NE flow to not quite be as warm as it could be for Dorset into east Devon (or highest temps more limited to near the coast here), limiting potential. Looks that way on satellite image and observations, hope I'm wrong though. Saw a very distant small tower turn into an anvil to the NNW, and larger cu to the west and distant NW ( the latter from convergence nearer the north coast of Devon probably) I might drift west as think it may happen there before here anyway, if anything does happen here. bit of a risk though.

To the far north I believe I can see the edge of the spreading/thinning anvil from the Midlands storms! It has spread to about Gloucester and the satellite shows nothing between that and me. We did had 2 thunderstorms yesterday evening with quite frequent thunder/lightning (more visible from the 2nd storm as it was night then), but it was nearly all sheet lightning and they passed through quite quickly. I can't complain really, but it's hard not to be a little jealous of today's storms and last night in the SE.

A few pics, first looking east showing this cell in its infancy, 2nd looking east a few mins ago showing more developments, and the 3rd looking west a few mins ago towards where the thunders coming from Thunder is much more frequent than Blitzortung is showing, but sounds quite high up within the cell with most being quite short rumbles.

Woah, it's just switched on, what just went over has suddenly started producing frequent rumbles!

Here we go, really bubbling up now including a little bit of glaciation which just came overhead and we had massive convective rain drops for a minute or so.

Some cumulus (or perhaps lowish based Ac Cas if it's come off the sea) that's recently appeared are getting bigger and more bubbly i.e 'congestus' like quite quickly.

I noticed this bit of text earlier: "Note: bifurcating flow tends to leave a gap between two main clusters of thunderstorms" http://convectiveweather.co.uk/forecast.php?date=2018-05-26 That will be here then Hopefully not, but been there a few times in recent years. A fair bit of mid level cloud recently, including some Ac Cas, starting to clear more now. No sign of anything to my SE on satellite but it's early, wasn't meant to really get going until this evening.

Warmest air not quite reached here (as ever), it reached 21.9C but a fair amount of mid level cloud recently. However it's clearing a bit and may well get a little warmer. Lower surface temps shouldn't detract from any elevated storms this evening though, one hopes.

I know about the climate and Geography of Scandinavia, but it still can feel annoying when you've just had an apparent big downgrade. It still looks like a very notable month for them though. Cities like Stockholm and Oslo have similar summer averages to central/SE England (and the record maxima aren't any higher, 36C and 35C, (for the entire countries it's 38.0C for Sweden and 35.6C for Norway)). In May the records are 29C for Stockholm and 30C for Oslo. It seems to have been pushing mid-high 20's much of the time recently, varying in distribution slightly as the high drifts around. Oslo is forecast mid-high 20's continuing for the next 10 days (May average maxima 16.5C). GFS (which seems to underestimate at least for the UK) going for around 28C in some areas most days, with the odd 30/31C). Thankfully though, it seems my moan was a bit premature with a warmer airmass and offshore flow staying for at least part of this week, meaning some warmth and thunderstorm potential. It doesn't look too bad after that too. I'd be happy with that.

Yes it was a bit of an IMBY post as I wasn't a very happy bunny this morning. It would be nice if this area could join in with warmth and storms, we will see.. shows it might not be nationwide though.

For those that don't understand some posts like mine this morning, here's the ECM 00z derived forecast for my location: Those are 1pm temps so maxima could be a degree or two higher.. but even so, it would be very disappointing if something that looked very good ended up not being much better than average really. Hopefully it was a bit of a rouge run.. but even the Met Office's own forecast isn't much better for me, slightly warmer than average, a fair bit of cloud. Of course the change on the ECM 00z probably makes less of a difference further north/east, but it makes all the difference down here.

Well here come the downgrades. In fact it's been downgrading gradually for days, more and more cloud, and lower temps. Sunday and Monday only 20C on the Met Office for here now, and an onshore breeze when it looked like being offshore before. In fact on the ECM the circulation is now turned more westerly and we've lost the 10C 850's at early as t+72 down here.. might manage one very warm afternoon but probably not! A bit better further east, but downgrades most affecting here of course. Also this month here is not a patch on what Scandinavia is getting. Why is is always so much easier for even them to get high temps etc as soon as May arrives, even if we're under similar uppers? GFS has been showing at least mid-high 20's at times for parts of Sweden/Norway for weeks it seems (even into Lapland at times) and I've seen up to 32/33C shown there. Really does feel like everywhere else really does get it better, basically all the time (apart from maybe Iceland..).

UKMO and especially ECM are a very big last minute downgrade down here, gone is the 10C+ uppers as early as t+72, and E/NE drift, and storm potential. Just more 'normal' conditions instead. Why can't these charts be right for once We might not even get a very warm day here now depending on cloud etc,, or only one.. and only one shot at any thunderstorms on Saturday night... Probably quite an unremarkable spell while even most of Scandinavia, even up to Lapland at times find it far easier to get higher temps than us (even under similar uppers). If it seems too good for this country, it probably bloody well is!

It doesn't look too bad really, a relatively average mix of conditions.

Thanks. It is a bit odd how other studies have not found the same results as in the UK (does the CSD1 sensor have different characteristics to the CSD3? Can the Met Office change the 'threshold' etc of the sensors in any way? or maybe all the hot air from jet engines causes more convective cloud build up ) Your last bit does sounds strange. It appeared something's up, the equipment change raises suspicions further for me and then that UK article seemed to back it up. Would be good to see nearby records with the same instrument but I'm not sure if they're available and don't really have time to look atm. Anyway, with regards to previous summers, I was looking at data for Exeter Airport and ironically in 1976 a warm up around the 19th April, a min of -1C on the 1st May, and then a warm up to 23C here around the 7th May matches this year very closely indeed. Probably just coincidence though.

This was my 11th April of recording data (2008-2018). At this location 2018 was the 2nd warmest for average temp (+1.7C above the 1981-2010 average), the warmest for mean minima, and 'only' 5th warmest for mean maxima. Despite that, the 14.0C mean maxima was still nearly 1C above the 1981-2010 average. Yes much of that was due to the warm few days, although most months have warmth balancing cold to a greater or lesser degree.. anyway I'd prefer what we had to constant 14C maxima all month. The Met Office maps do show that it wasn't 'that' warm maxima wise, with minima being the more notable thing.

That's interesting as it was CS sensors giving higher totals that I first became aware of (I believe from posts on this forum many years ago). Maybe the UK just has a particular climate with much more intermittent summer sunshine than many places. The logical conclusion to those figures, is the current Heathrow data is un-corrected (as they state), and they had previously published 'corrected' figures. The paper does state that the average 170w/m2 threshold for the CS recorder compared to 120w/m2 for KZ would in theory mean the KZ gives slightly higher totals, but as radiation changes rapidly at sunrise and sunset this would only be a few minutes, and this is outweighed by the above. I suppose you might get a scenario with weak sunshine through high cloud where a KZ sensor registers sunshine but a CS recorder doesn't. I'm not sure if/how different KZ sensor versions vary if other studies have looked at different versions though? Then there's variability with CS thresholds apparently ranging from 106 to 285w/m2, and human interpretation of the burn marks on the cards. There could have been more 'sunny start then shower or cumulus infill' days due to synoptic in recent summers (not sure how easy it is to get the data to assess that), and maybe it would have also kept the coats of the SE clearer.. (but to that extent over a 10 year mean?!) However, if the deficit at Heathrow is genuine, presumably some nearby climate stations around the Home Counties/London area would show a similar decline, if any have kept using a CS srecorder to date. That's the only thing that would stop me thinking there's something fishy really. But without that, I think that Met Office associated study of 16 stations having simultaneous recording using both sensors is pretty strong evidence supporting what's already quite apparent.

A sea breeze kept us slightly cooler than some areas this weekend, reaching 20.2C, 22.7C and 23.7C yesterday. Still very warm and lovely though. Cool nights with mins 4.2C, 5.1C and 5.9C. Much better than the North coast too, there were some big contrasts across the SW peninsula this weekend. Fog this morning that has now lifted/thinned a little to low cloud, min 8.3C.

But even for the SE and central South region, the sunshine anomalies are much higher (this is using the 1981-2010 average). 2008: 576.4 - 94% 2009: 619.1 - 101% 2010: 602.8 - 99% 2011: 550.3 - 89% 2012: 509.3 - 82% 2013: 694.4 - 112% 2014: 710.2 - 115% 2015: 599.2 - 97% 2016: 574.6 - 93% 2017: 653.2 - 105% Average: 98.7% Heathrow average: 85.1% Has Heathrow really sustained a 13.6% sunshine deficit compared to even the region it's in, over a 10 year period? Well I know I've mentioned this before but I don't think so.. Heathrow of course changed from a Campbell-Stokes recorder, to a Kipp & Zonen recorder in September 2005: https://www.metoffice.gov.uk/pub/data/weather/uk/climate/stationdata/heathrowdata.txt and the Met Office state on the Historic Station page that "No allowances have been made for small site changes and developments in instrumentation" Studies in the UK shows that CS sensors give higher sunshine totals, for Example: https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1256/wea.99.03 This study aimed to create a conversion factor between the two sensors in the UK using an overlap of data using both instruments at 16 stations for an average of 18 months. It found that the CS recorder overestimates sunshine due to the spreading of the burn marks, primarily with strong sun and broken cloud conditions, by an average of about 20% in summer, and 7% in winter. It's studies like this that the Met Office use to try keep their data-sets and maps consistent (that Heathrow data often seems to disagree with). To me this is the only logical explanation and makes perfect sense, I'm sorry but I can't see otherwise.

No idea what this summer will do.. although referring to the list of factors quoted on the previous page, the summers ending in 8 thing is of course a coincidence and if Easter had the same dates as last year it would have been warm instead. But anyway there's the usual negative postings.. I've posted the maps before but the last 5 summers have actually been a relatively standard set for the UK.

I've actually quite liked this spring, the variety from the March 'beasts' to the very warm spell in April has had a more continental element to it. On the 19th March I woke to 15-18cm of snow and on the 19th April it reached 23.6C here. Ok March was very wet and a bit dull but with some interest and the snow, I didn't mind so much. April has also been a bit duller than normal but we had that 5 warm sunny days and then thundery activity, and it looks like another warm up is coming. I prefer a spring that warms more strongly rather than starting off above average but staying homogeneously mild, or warming slowly with cooler April/May's relative to their averages. I know it's been worse for sunshine levels in some other areas though.

A min of -1.1C here, first air frost since the 30th March and 0.1C off my lowest May temp (covering the last 10 years). A clear calm night is something the 'beasts' were missing, shown by how this is only 4.2C higher than the lowest I had then. There's apple orchards near here, but thankfully most varieties seem to be holding off for the warm up that's coming (this morning's frost won't have affected them too much though and it will have been slightly warmer on the hillside).

It feels like there has been a slight increase from 2012 onwards here, in comparison to 2007-11, (though I remember one nice event May 2011 thinking about it) I can remember major storm outbreaks across the UK every year from 2012 onward, usually more than one, though they don't affect everywhere of course. In late May last year I saw the most frequent, but distant lightning I've seen. New flashes every 1-2 seconds, constant strobe lightning to the SW and W. A decent thunderstorm skirted us in July. We had a few weaker events and then some activity at the end of Dec 2017 and early Jan 2018 too. Of course there was last weekend too, although that mostly went around me. Despite this there seems to have been a genuine decrease shown in stats like those from TM. I have wondered if cleaner air might play a role.. not sure how significant that is compared to e.g. more plume events missing us to the east. There's definitely a lot of studies on the link between aerosol loading and lightning production (via changed cloud properties, even along shipping lanes). However whether aerosols cause 'new' thunder events as opposed to increasing flash frequency in storms that would exist anyway, I'm not sure without doing further reading.