WeatherArc

It was amazing, pretty much at 3pm everyday explosive thunderstorms would roll in, i would love to upload some of the videos i got from my time there however for some reason it wont convert the files.

Highly detailed vid by Trey Greenwood documenting how the fires spread and what caused them, well worth a watch.

12z GFS follows the 06z run in showing favorable conditions for widespread thunderstorms/ supercell development Not often you see 2000 j/kg of sbcape and widely 60+ knots of bulk shear. Its just annoying the winds at 850mb are so low, perhaps models will start to catch onto some mesoscale/surface features as we get closer. A hodograph taken from the north sea shows what we could have if those 850s shift a little Westward. The lack of low level shear will hinder anything tornadic and as @Eagle Eye stated the weak inflow layers and the lack of surface-based buoyancy will hinder hail. However the strong bulk shear and hodographs that vent precip away from the updraft base should allow for development of LP supercells. Could be a few photogenic storms around should this come off.

Seems a bit of an extreme temperature gradient on the 06z GFS 37 across the channel yet barely 30 in most of the country?

Very good run from the 06z GFS Widely 25+ temps across England will combine with 18 degree+ dew points and decently steep lapse rates (especially in the south) This will result in around 1500 j/kg of sbcape across the central and southern parts of the country. Incredibly good bulk shear values will increase a possible supercellular threat especially in the central parts of the country where storms can tap into both the cape and the 50+ knot bulk shear. However, a lack of low level shear may disrupt this threat, especially when combined with the weak effective inflow layer (I think this is the GFS overdoing things). If supercells do form i would expect them to be more of a hail threat than anything tornadic. The only way i see cells becoming tornadic in these type of conditions would be through constructive storm mergers that can increase low level SRH. I did want to quickly mention this hodograph, 53 knots of 6km shear would favour LP (low precipitation) supercells as strong upper level winds will allow for any precip to be ventilated away from the updraft base, could make for some pretty amazing views.

Its actually teasing us at this point Another run from the euro bringing high cape, the question is has it sniffed out something or will the downtrends start? I know my answer

Just your average 28 degree dewpoint across the channel, seems to be an increasing theme of high dewpoint values on the euro for some reason, considering 20+ is usually considered rare in the Uk even in the summer its an interesting trend. Maybe some side effect of that marine heatwave we had earlier in the year?

Does anyone know if there are any temp/dewpoint/wind or any other surface charts for this day? Im guessing skew-t charts weren't around then. Would be very interesting to view. Also I quite like going back and looking at /analysing past weather events so if anyone has suggestions of any tornado/convective themes it would be great to hear them

Its possible, models have really downtrended any supercell potential. Ill keep an eye on it but it doesnt look great right now. For supercells to form we need both windshear and instability, 4000 j/kg of cape is nice but without any shear your just gonna get regular thunderstorms, 2012 was unique as we were in a rare position of having both enough cape and shear, something we haven't seen in this country for a little while.

Ill come back to this after we get a 2 mile wide EF5 wedge on saturday

Well the last euro run i looked at had 4500 sbcape in the west mids. This run has barely 50 Lets hope the next few runs of both the euro and gfs will be kinder to us storm lovers

Thank you , I didn't think to check on youtube for any videos, very informative and interesting. The report of a secondary storm forming before the main supercell produced the tornado makes me think a constructive cell merger occurred, increasing near storm low level SRH and greatly aiding tornadogenesis. The same thing happened on the 28th June 2012 near Sleaford, and to a more extreme example in Joplin 2011 Metweather on twitter made an absolutely amazing radar breakdown of the Sleaford tornado, can see how that merger helped the supercell produce by increasing near environment helicity, wonder if the same thing happened here?

Hey guys, while we are in a dip between any potential heat and storms next week I decided to do some research into the deadliest and one of the strongest tornado outbreaks on record in the UK, the 1913 outbreak that affected parts of Wales and Western England. This outbreak would record 5 strong tornadoes, 3 rated F3/T7 and 2 rated F2/T5. Atleast 6 people would die and over 150 were injured. An interesting thing about this outbreak was when it occurred, October the 28th. We usually associate strong thunderstorms/tornadoes with the summer heat and instability however this isnt always the case in the Uk. Looking at the data most tornadoes occur within the Autumn with only a few notable exceptions (Birmingham 2005) Going back through reanalysis, a large trough with an attendant area of low pressure was situated to the south west of the country, this positioning allowed for direct southerlys to pump heat northwards creating some unusually warm conditions for the end of the month, temperatures widely over 21 °C were recorded with some spots even higher. The 850mb map shows most of the country under the 8 degree isotherm, with parts of the south east under 9. This unusual warmth combined with Atlantic weather fronts to create some unusual Autumn instability. I would expect instability to be in the 800-2000 j/kg range, given the steep lapse rates and 20 degree plus surface temperatures. The devastating South Wales tornado of October 27th, 1913 WWW.GEOLOGYWALES.CO.UK This paper by geology wales details the event in great depth and i would recommend people take a read if they want to research this event further. The first reports of a storm came at around 16:00, with a weather spotter reporting several flashes of lightning followed by "a terrific hailstorm such as the oldest inhabitant never remembered having seen" The storm lasted around 10 minutes before moving off to the North East, hitting areas of Somerset before crossing the Bristol Channel and hitting areas in the Vale of Glamorgan. It was this storm that went on to produce the deadliest tornado in the Uk, killing 6 and injuring 100 in and around the community of Merthyr Tydfil. The exact wind speeds of the tornado are unknown however by using the damage an estimate of over 160 mph was made, this would equal a high end EF3 on the Enhanced Fujita scale. The storm itself was in my opinion was an extremely cyclic supercell, producing multiple strong tornadoes. All reports of tornadoes on this day came from this cell, it likely produced over 10 tornadoes as it tracked over Wales and North-West England. Unfortunately i cant find any photos of this supercell or any of the tornadoes it produced. After Merthyr Tydfil this cell would produce another EF3 in Abercynon, this one was likely as strong as the previous tornado, A high-end EF2 in the Taff valley, and another EF2 (low-end)that struck the outskirts of Shrewsbury, the final strong tornado this cell would produce would be in the Runcorn area at around 20:30, this EF3 would cause large amounts of damage as it struck the town. This cell also produced 10 other weak tornadoes throughout its life, all of these were rated EFU. My (badly drawn) guess of the track of the storm going off reports. Some interesting meteorological points, the low pressure system off the coast was reported to be rapidly deepening, a pressure of 990 millibars was reported at midnight of the 27th, by 18:00-as the storm was near the Bristol Channel, the pressure had dropped to 975 millibars, I wonder if this rapid deepening of the low helped accelerate the 500mb winds, helping increase Bulk Shear values and therefore increasing favorability for Supercells with all significant hazards. Something else i find interesting was that a South-east wind was reported at the surface. South East winds at the surface and southerly winds at 800mb would allow for ample directional shear, especially if combined with the speed shear from the strengthening jet coming out of the West/South West. This shear at the surface would allow for significant veering and backing of the low level winds. For anyone who doesn't know about veering or backing and how it can increase tornado likelihood, l will try to explain it using some old charts pulled from the US. This chart to above shows wind barbs, one long line on the barb indicates 10 knots, half a line is 5 knots and a triangle is 50 knots, for further info the NWS does a very good job at explaining them. Information about wind barbs WWW.WEATHER.GOV To the right of the barbs there's some horizontal lines in different colours, red indicates the winds from 0 (surface) to 3km up in our atmosphere, green indicates 3-6km, yellow 6-9km and blue 9km plus. Notice at the bottom of the chart the wind barbs are pointed to the north west, while at the start of the green lines they are pointed to the North East, this change of direction at the low levels (veering) dramatically increases tornado probabilities, especially if the winds right at the surface are backed (where the wind comes from a southerly or southeasterly direction) You can see here from this chart taken from the USA that the turning of the winds in the low levels allows for a large, clockwise turning hodograph supportive of violent tornadoes So if surface winds were out of the south east, and the winds at 500mb were from the South west we likely had some decent backing at the surface and veering aloft. However, I believe that the tornadoes in South Wales were dramatically aided by the valleys, we know from tornado outbreaks in the Appalachians that valleys can act as localised sources of backing, as they funnel winds through them. The fact that the strongest tornadoes occured within the valleys makes me suspect this increased backing aided in the storms tornadogenesis. The tornado at Merthyr Tydfil was reported to be 50 yards wide when it first touched down near Efail Isaf, as it tracked northwest it strengthened and considerably widened to over 300 yards wide near the community of Treharris. The forward speed of the tornado was around 35mph. This is an account by a meteorologist living in the community of Edwardsville, near Treharris- "At 4.30 p.m. the wind, a gentle breeze, was from S. by E and by 5 p.m. was due S. At 5.15 p.m. a dead calm set in. The sky from 430p.m. was heavily mottled with dark patches of cumuli in the South, but these clouds presented straight edges in the SSE. It was a "troubled" sky. To the South, as the twilight advanced, a dark sullen sky was noted. The cumulus form had disappeared except in the East, where a heavy mottled appearance was still observable until darkness came swiftly. During about half-an-hour of calm the atmosphere was oppressive, giving one a sense of great uneasiness, and a remark was made that rain would probably ease the tenseness.Rain began to fall at 5.20 p.m. The first flash of lightning (red) was noted at 5.25 p.m., coming from a dark cloudbank in the South The rain ceased in about 10 minutes, and the red-coloured was followed by intensely blue lightning, flashing at frequent intervals. Very few peals of thunder were heard, these being sharp, with an absence of reverberation, and from about 5 40 p m the thunder was not evident. The blue lightning was appalling. When the flash occurred, which was most frequent, there seemed to be three or four interweaving flashes, all of a deep blue, and, what was strange, the waves of blue fire seemed to be rolling on the ground. A few seconds before 5.50 p.m. we heard a noise resembling the hissing of an express locomotive. The sound grew rapidly in volume, at last resembling the rushing speed of many road lorries racing along. The oppressiveness that had been previously noticed increased, and the heat and air-pressure were pronounced during the rushing noise. We endeavoured to move out of the room to the passage for greater safety, because a hurried remark was made that the engines of these supposed passing loaded steam lorries had collided before the house, and were about to burst, when the panes of our windows were broken by stones, tiles, slates, dried cement, and splintered timber. The missiles broke the Venetian blinds and struck the opposite walls. We made for the rear of the house, but all the windows were being bombarded also by small material and corrugated iron sheets. We could distinctly hear the chimney-pots fall on the roof, and the material sliding off being dashed on the pavement and doorstep. We could see the kitchen clock from the hall passage. It had stopped at 5.51 p.m. It was not struck by any object. It is the largest clock in the house. Two smaller clocks in other rooms were not affected. After this crash had ceased (this only lasted from 60 to 90 seconds), rain fell in torrents. The lightning set fire to the tar which had been sprayed some three weeks previously on the main Cardiff and Merthyr road, some 12 yards from our house door. A distinct smell of sulphur pervaded the air. The lightning continued fitfully and much less intense for about 5 minutes after the climax of the storm had passed, and thunder occurred during the rushing, crashing, roaring noise." This plus some other interesting accounts can all be found on the geology wales link I posted above, would recommend a read of the accounts by people after the tornado past. One thing i'm surprised by is the lack of fatalities in the third and final F3 tornado that hit Runcorn at around 8:30-9, nighttime tornadoes are known to record higher levels of fatalities, with notable ones such as Greensburg in 2007 and Mayfield in 2021 causing catastrophic fatalities, even a tornadoes of similar strength such as the Bowling Green EF3 in 2021 killed 16 people. The fact that a strong tornado hit a major population area and only injured a few is a miracle. Some damage photos from the outbreak. Tornado WWW.ALANGEORGE.CO.UK There's quite a few photos on this site of the damage. I'll try to find a few more articles, if anyone has any charts or accounts from this then please feel free to post them. The fatalities from this outbreak are very inconsistent, geology wales says 3 while wikipedia says 6. Sorry about any spelling mistakes, i've had about 2 hours of sleep so there's probably plenty in there

Spot the difference between the Euro and GFS... The GFS has a much stronger high across Iberia, this blocks the jet and allows for a ridge over us, this would allow for a few days of warm-hot (depending on jet position), settled weather. On the other hand the Euro has a weak high, this allows for a trough to move in and the potential for a spanish plume type scenario with a low forming in the Bay of Biscay and pumping heat, humidity and thunderstorm potential northwards (this is shown in the 12z euro run above) . I believe at least a day of very warm-hot weather is likely now we have major models and ensembles on board however its difficult to say if it will be settled or thundery, the high pressure area over Iberia and the strength of the ridge will likely be the deciding factors. The euro run tonight will be interesting. Any major thunder potential will likely be between Friday the 18th and Monday the 21st

It's an interesting thought, i've always wondered how global warming will affect thunderstorms in the UK, i mean we know a hotter atmosphere can hold more moisture so maybe higher dewpoints and PWAT values will become a part of summer. I also agree with you about next week but i can dream

Im not familiar with MOGREPS but it seems to be sniffing something out at the end of its runs. The Euro 0z run is largely the same as the 12z, with parts of the UK still getting around 3000 j/kg of cape so thundery weather still very much on the table. The only major difference here between the runs is the low out in the Bay of Biscay. 12z has a closed low develop while the 0z has a large open trough. The closed low would allow for higher 500mb winds around its base and therefore better transportation of heat and moisture northwards. Its not a major difference but you can see how it affects the northward extent of the heat in the UK. It also affects how long the heat stays, 12z has it still in place at the end of the run while the 0z has the trough move in and clear the heat out by Sunday night. Meanwhile, the GFS is in its own little fantasy world It seems to be all over the place at the moment, while i think every run needs to considered the euros consistency as well as the MOGREPS ensembles makes me think a very warm-hot solution has better chances of winning out right now. And if your a thunder fan i will note there's still some very interesting ensemble members from both todays 0z and last nights 12z Im pretty sure if we ever got 6000 j/kg of cape in this country it would be quite a memorable day Hail the size of grapefruit anyone?

This is complete, utter insanity from last nights 12z Euros members. Member 48 showing a casual 6000 j/kg (yes, 6000) of cape above Bristol Updrafts with the same power as about 10 nuclear bombs. This must be some sort of model record? To see a figure like this even modeled in the UK is just crazy, I did a double take when I first saw it And if that wasn't enough the control and members 13/35 are showing an environment with wind fields supportive of violent supercells and possible strong tornadoes. Have we suddenly switched climates with oklahoma city in may??? If this came off I would never complain about the summer of 2023 again

Just depends if we can get some wind shear into the mix, theres some over the Irish sea and the gfs has previously floated the idea. Not the best profiles in the world (from last nights gfs run) but shows that there is the potential for some decent speed/directional shear. With 4000+ j/kg of cape any kind of shear/low level winds would need to be watched.

Sorry am i looking at the UK or Florida I have never seen a 25 degree dewpoint in this country, its rare enough to get over 20 even in the summer... What a crazy run.

A point about the latest euro run, while i doubt we could reach 40 degrees at this time of year imo there's a good chance that heat indexes (how hot it actually feels like) could pass the 40 mark. Unlike last year where we had dry air with dew points in the single figures, the euros run shows them incredibly high (20+) with most of the country feeling very oppressive, relative humidity values are also pretty high (70%+). So while i dont think we have a chance of another 40 this year, if this scenario plays out we could well breach some heat index records. And as pointed out by others here the cape values are incredibly high, if not record breaking on this run, would be some explosive thunderstorms if this happened.

4700??? Blimey even in the US plains that's considered a high value. The period from the 17th-20th is really starting to get my attention, especially now that the euro and GFS are starting to agree on a few runs. Moderate-Big cape and some decent wind shear about, 2012 round 2

Not sure what the 18z GFS run last night was smoking but I like it *Soundings taken from around Stafford and Welshpool. Haven't seen EHI at those values for the UK in a long time. Pretty much perfect ingredients for UK supercells, 2000+ sbcape, widely 40+ kts of Bulk shear and some steep lapse rates. 850mb winds may also be marginally supportive of tornadoes given a veering wind profile. Think everyone here would be very pleased if this came off. Perhaps a sign of an explosive end to August? I mean its way out at the end of the runs and the 0z/06z runs have the cape stay down in France but runs like this one have popped up over the last few days. Defo one to watch IMO.

Sounds like Reed has had a close call with a violent, deviant tornado in Colorado. Hes ok but has had his rear windscreen blown out. He also seems to of lost his shirt Tornado wedged out but has since occluded and dissipated, the supercell continues to cyclically produce tornadoes.

Wow, that colorado cell is absolutely crazy, i didn't expect anything like this today. Reed reporting an extremely deviant and strong tornado. Extremely cyclic cell as well. Vince and Reed still live and covering it.

Updates on tmrws severe weather potential. Both the HRRR and NAM 3km now agree on a potent environment ahead of a developing cold front, questions still there over 3cape, lapse rates, morning convection and capping however the potential for a very rare August severe weather event is increasing. The main threat area seems to be Eastern Oklahoma, Southern Missouri, North-Central Arkansas and extreme South Eastern Kansas. Hodographs that wouldn't look out of place for spring. Both models are also showing a discrete/semi-discrete storm mode with 2-5 supercells developing either on the front or in the open warm sector. Profiles that wouldn't look out of place for April or May, 35+kt 850mb winds will allow for large, curving hodographs with 0-3km helicity widely above 480 m/s. This combined with widely 3000+ j/kg of Sbcape will allow for supercells with all hazards. I would keep an eye on 3cape however, seems to be a distinct lack of it. This may hamper tornadogenesis.