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Showing content with the highest reputation on 14/08/20 in Posts

  1. 24 points
    *** USING THE ECM TO FORECAST TEMPERATURES IN A HEATWAVE - A REVIEW *** I often make predictions based on models several days ahead, and then I find it useful to revisit these predictions after the event to learn for next time. Those who follow my posts know I like to use the ECM to forecast temperatures. Although I find them to undershoot actuals, the point is that the ECM op often picks up on the general trend several days before, and at very least undershoots actual temperatures in a fairly consistent manner. My idea is, if I can work out how much the ECM is likely to undershoot temperatures, it is then possible to adjust the raw values to make an informed prediction in future events. This particular period was of great interest because, very early on, several ECM runs suggested an extended period of extremely hot days for the UK, including a fresh attempt at a UK temperature record. So how did it do? I'm interested in two things 1. Did the ECM (generally) have the right idea about what was going to happen with temperatures at an early stage 2. Was my idea that ECM raw temperatures generally undershoot the actual maximums by 2 to 4C? I've gone back through the MOD threads and found the following predictions from the 12Z run raw maximum values (obtained after each run from weather.us) from August 1st, 2nd and 3rd August - I provide the raw values here, not my "adjusted values". Then, I've listed the "on the morning predictions", which were the maximum "raw" values predicted on the 00Z runs of the same day as the forecast was for - this is followed by the actual maximum, and the difference between the raw and actual. AUGUST 1 (12Z run) Thurs 29 [T120] Fri 33 Sat 34 Sun 37 Mon 35 Tues 34 AUGUST 2 (12Z run) Thurs 28 [T96] Fri 32 Sat 32 AUGUST 3 (12Z run) Thurs 28 [T72] Fri 32 Sat 33 Sun 31 Mon 34 Tues 36 Weds 35 ECM” ON THE MORNING” / ACTUAL / DIFF Thurs 28 / 30 / +2 (Northolt) Fri 34 / 36.4 / +2.4 (Heathrow) Sat 33 / 34.5 / +1.5 (East Sussex) Sun 33 / 34.0 / +1.0 (East Sussex) Mon 33 / 35.5 / +2.5 (Heathrow) Tues 33 / 35.7 / +2.7 (Heathrow) Wed 33 / 35.4 / +2.4 (Heathrow) Thurs 29 / 29.8 / +0.8 (Portmadog, a totally different location!) MY SUMMARY: For my first question, did the ECM spot the trend early on, I would say definitely "yes". It had already seen the longevity of the heat even out to D10 on the August 1st run. I appreciate some of 00Z runs were less certain about this longer period, as was Aug 2nd 12Z, but as it is quite unusual to get a plume that gets trapped for several days over parts of the UK, in my opinion it was quite impressive that the ECM had alerted us to this possibility so early on, even if it did slightly overdo the heat in the latter period of the heatwave. If one averaged out all of the runs, 00Z and 12Z between the 1st and 3rd, though, I think you'd probably have got a fairly accurate picture of what the raw values were to be predicted by T0. Bear in mind, at this stage, the GFS was predicting 23C or 24C maximums after Saturday 8th!! On the second question, I'm mostly interested in comparing the "on the morning" figures to actuals, as taking a prediction from August 1st, for instance, may have varied from the actual due to modelling error, not systematic undershooting of temperatures. Using this comparison, one can see that raw values undershot actuals by between 1C and 3C. This was a bit lower than I'd expected - in the past, between 2C and 4C works. My tentative ideas for what has happened here are as follows: - A high level of uncertainty due to thundery outbreaks and cloud levels make it very difficult to forecast temperatures correctly. Yesterday, the ECM raw values actually needed to be adjusted downwards in areas where cloud and rain was more extensive than forecast. My sense is that the ECM has done this before. So, conclusion 1: In future thundery outbreaks, I will not assume there will necessarily be any uplift on raw maximums at all, and I will continue to analyse this specific context. - On Saturday and Sunday, the raw maximums were forecast to be in the Sussex countryside, and only a 1C to 1.5C uplift was observed. I studied private weather stations in inland Sussex that day, and they were a good 2 or 3 degrees up on all other areas even in the South East and London. I suspect that the raw maximums probably did undershoot the actual maximum by 2C to 3C (and there were genuine maximums of 35C and 36C), but the sparsity of official stations meant these weren't picked up. So conclusion 2: when the maximum is forecast for a rural location, do not take this as a representation of what the maximum official value will be. For that, stick with raw maximums in more urban areas, or airports. - On other days, both raw and maximum values were in or around London, and an uplift of 2C to 2.7C was observed. This is in line with what the relationship I have noted in the past between ECM raw values and actual values. So conclusion 3: Adjusting the raw values by 2C to 3C works when the maximum is forecast to be in a more densely populated area with numerous reporting stations. Of course further possibilities exist which could explain the difference in the adjustments needed; for instance, does the ECM handle heat levels in urban and rural areas differently? Also, I have noticed it doesn't have the best handle on coastal areas - my local station in Gosport was often 4C or 5C up on the ECM "raw" (and a number of other charts, too!) On the whole though, I am fairly pleased with my "project". The initial heat predictions which seemed so outlandish at D7/D8/D9 ended up not too far away, though not quite record-breaking. The idea of adjusting the raw maximum again showed to have value, though with some minor inconsistencies. Hopefully this kind of analysis will help us get an early handle on the next future heatwave. Expect the ECM to be the first to see the big picture, averaged out over a few runs. Expect the raw values to be a little too low, though take note of where maximums are predicted to be, and how unsettled the weather is forecast to be. And now back to the future
  2. 17 points
    Just did a 15 minute stint on BBC Radio Somerset on Storms if anyone can find the link might be worth a listen or bore you all too tears
  3. 15 points
    So had some fun finally last night, Cloud tops starting lighting up around 9pm out to my east over the Estuary but caught me by surprise how quickly they went up and could not get to my lovely Estuary Spot looking East for some Cgs over the Water. This Storm was throwing out some really nice Cgs as well. So headed up towards Chelmsford and a storm initiated over my head and whilst on the A130 north so much water on the road a Cg landed what must have been 30 feet away instant flash and crack just wish I had my camera rolling at the time. Plotted up at a nice farmland spot and just sat there and watched amazing anvil crawlers and big Cgs got a few on my Canon and will go through them over the weekend to see if my focus was sharp. I see in some respect the SOR / COS and TOD have all fallen in this Hot Spell so just praying the NE and Lincs can get some action now.
  4. 14 points
    One photo I took of the storm early yesterday at around 2am.
  5. 13 points
    What you have to take into account is the average UK Thunderstorm lasts 35 minutes and generally gains a height of 17,000 to 20,000ft. They work off around 250jkg to 750jkg of Cape and so rarely get to severe levels. Some of the Storms earlier in the week were working off 2000 to 3000 MU Cape and gained heights of 35,000 to 40,000ft and hence lasted longer gained more height were visible from 100 miles away and had continuous flashing with thousands of strikes. The SE were Unlucky with the Quality of Storms we got plain and simple. I would rate the breakdown in my back yard as a 1 out of 10 compared to previous years but some 20 miles south in Maidstone would rate it probably closer to 7. Its luck of the draw at the end of the day unless you go after and chase these things. The one I got on between Chelmsford and Brentwood last night I would rate a 4 just for the fun factor and nearly getting frazzled twice but then I am quite hardcore and won't think twice about core punching baseball sized hail in the States its a rental don't be gentle is the saying. Chin up everyone
  6. 13 points
    Only 5 storms? I’m looking for a wind instrument to play you a note on, but it’s so infinitesimally small that I can’t find it
  7. 10 points
    Hey Gang, I’m not the sharpest tool in the box / drawer / shed..whatever...as most of you probably know already..jeez I’m so modest!...BUT..I do know an early taste of autumn when I see one and there is emphatic support from the models so far today and in this case the ECM 0z ensemble mean to support it.,and I take absolutely no perverse satisfaction in saying that an early taste of autumn during late August is currently the form horse!
  8. 9 points
    Quick one from moi, very busy...... ..go figure....anyhoo the models, certainly the Gfs / Gefs / Ecm 0z show a change to much cooler and more unsettled for the last third of August, dare I say, an early taste of autumn awaits us?!!
  9. 7 points
    For all you storm starved, I present my rather squiwfy artists impression of lightning..
  10. 7 points
    Nice late afternoon storms here in Prague today, after a hot and sunny day. Saw 2 CG strikes hit the hill 500m from me, with some very loud shotgun thunder and deep booms. 15 minutes of torrential rain and some wild wind gusts. Very nice
  11. 7 points
    Biggest concern today was the extensive low cloud, which is rather stubborn to break. The most prolonged breaks so far have been in E Norfolk and NE Suffolk, allowing temperatures to lift to 24C at Tibenham Airfield in south Norfolk. Some gaps are also noted in SE Kent, and here temperatures have crept up to 23C in places. 12z Herstmonceux sounding suggests there is a subtle warm nose at ~850mb that requires a surface temperature of at least 22C to get past - many stations across southern England have not yet reached this threshold. The subdued temperatures have also meant not a significant temperature contrast between land and sea, and so the sea breeze convergence is only really evident across Kent/Sussex, and also Devon, otherwise the winds are largely offshore even on the coast. Without the convergence and >22C temperatures, surface-based convection is going to struggle to develop. Based on this, the most likely areas right now to see convection initiate are E and SE Kent into East Sussex, and E Norfolk into E Suffolk - I particularly like this location due to the length of sunny breaks here so far, and a small surface low that is located in east Suffolk. Anything that does fire here will then drift WSW through Essex and perhaps towards London during the evening. Convergence is also noted in west Wales which may combine with upslope flow, and the fact there has been more sunshine here, to trigger some convection too. The sounding reveals tall convection is possible (cloud tops potentially up to 36,000ft, which is quite deep for UK standards) but CAPE is rather skinny with fairly saturated profiles - and so lightning probably won't be as prolific as we've seen in previous days. As has been the issue all this week, shear is weak (10kts), and so storms will pulse and then collapse, bringing the risk of significant rain totals given their slow movement to the WSW (PWAT is 42.3mm!!) The Bury St Edmunds storm right now I suspect is still elevated given the cooler surface temperatures and lack of any noticeable surface convergence there. Herstmonceux suggests ~800 J/kg if temperatures get to 24C. Edit: obs just updated and the sea breeze is beginning to show signs of developing along other south coasts in southern England
  12. 7 points
    Right folks a little bit of cheer from me this morning, don't get to down about the conditions becoming more unsettled over the next week or so. Last night's EC weeklies were pretty positive, especially for the South come the end of the month, High Pressure is ridging nicely at times, and this pattern continues to hold into Mid September. There will be a risk of more unsettled conditions towards the NW at times, but there looks to be a decent amount of settled and at times warm conditions for many. I was almost expecting to see a barrage of lows spreading West to East, but it's not the case.. Perhaps a chance to take a late Summer break if this comes off. So all in all, the longer term outlook remains pretty positive. Enjoy your Weekends.
  13. 7 points
    The camels have now left and the nomads have removed their tents form the arid land. The Mid Essex Desert is no more. Heavy rain from 10.00 pm for an hour or so with strange flashes in the sky, From memory I believe it might be called lightning.
  14. 6 points
    Very impressive MWB, I do like to see folk do checks such as this. Checks like this really do help our understanding of any model. So thank you, and indeed ECMWF was pretty impressive compared to GFS it would seem. It might be as well for us all to remember that UK Met consider a temperature forecast 'correct' if withing 2-3 C of the actual, in general terms!
  15. 6 points
    Here's the first part showing Monday nights storm at Silverdale in Lancashire showing highlights of frequent bright flashes of lightning and loud rumbles of thunder as it started from around 11pm and lasted till about 5am
  16. 6 points
    Pal that was bloody unreal. Got home a short while ago, never seen rain so intense, and the lightning was bloody amazing! Basically I'll run through everything. About half 9ish I started seeing lightning every couple seconds to the S, SW, looked at net-weather and saw the storms on their way from W London, but as per, the stormshield of Beaconsfield and the Chalfonts was in full effect once again! Anyway, spent 10, 15 mins looking SW out the window and then just thought sod it I could bolt it now down the M40 onto the A404 Marlow way, and maybe head further south/west. Anyway, soon as I hit the M40 the lightning was in full view....unbelievable blinding flashes! Then I got to the A404 by the big roundabout in Wycombe and tbh it was NASTY to drive on! Rain like I've never seen before. I was doing 30 or so, surface water everywhere, every so often some BMW or t*t in a fast car would drive past much quicker and I just sighed....anyway, got to Marlow, torrential rain and lightning the whole way there.....parts of Marlow were a bloody torrent. I drove through the high street and started going down some road (yes down, a slight gradient) and noticed some dude turning around, so even though I have a 4x4, means nothing vs feet of water so I turned round too as made more sense to go back where I've come from up hill rather than drive to the bottom of a road where water is flowing down like Niagara effing Falls! Anyway, by the time I got back on the A404 to Wycombe it was still raining heavily but surface water had subsided slightly. Got onto the M40 home and drove past some t****r who'd taken a Lambo out on the M40 only to cause a lane closure and have a group of police cars at the side of the road with him....when will people learn?! It's like the beamers and other RW drive cars you see in the ditch on snow day....saw it once near me and just laughed, they don't know how to drive in these conditions..... By the time I got back to the village though, all was not over.....In fact the deepest water I had to drive through was in a notorious dip down the bottom of some lane and some dude with a hatchback was pulled up hazards on. I literally struggled in my jeep, battery light came on and all, but the jeep got me home as it always does come rain, snow or mud. What a night!!!!! Unfortunately, I have no DSLR shots or freeze frames of bolts, but I have numerous videos and freeze frames of flashes, mostly to the sound of Metallica.....lol.
  17. 6 points
    Well guys, thought I’d have a cheeky little trip down the M11, just at stansted and it’s epic! Bright blue lightning, and the roads are getting pretty bad. Mad how foggy and murky it is at the same time however, didn’t start seeing the lightning until it was right on top of me all of a sudden! Quite creepy and eerie
  18. 6 points
  19. 5 points
    “I’m afraid the X-ray shows that you may have eaten a tornado. Have you been experiencing particularly bad wind? “
  20. 5 points
    ECM Clusters today - I had been following the small chance of a mini-plume next Thurs/Fri, but I think the chance of any noteworthy heat last next week has diminshed, not increased. The T144 and T168 clusters don't allow enough time for hotter air to work northwards before the Atlantic trough shows its full force for the UK, and I doubt we'd seen any more than one slightly warmer day in eastern areas. Further out, I'd expect rain and wind on regular occasions based upon charts like this (D12). Again, might scrape a warmer day in the SE at times. The whole D11-D15 is fairly similar to this, btw...
  21. 5 points
    It's almost like the weather's getting political. Kent votes for Brexit and then sees far fewer imported storms from Europe!
  22. 5 points
    I think it was more to do with a complete lack of shear in the environment to aid storm organisation and longevity. As you can see from my photo of the "Basingstoke cell" - it was largely outflow dominant with an arching gust-front which blew itself out and collapsed not long after.
  23. 5 points
    Overnight storm here in Hadleigh, South Suffolk at around 01.45 am. Delivered 15mm of rain over about 45 minutes but not excessive amounts of T&L. Nice storm impacting Norfolk this morning: 07.05
  24. 4 points
    Send it our way please! It is 18c here in Reigate, heavy overcast, and even if a storm erupted here it would give up and b*gger off through depression. The parakeets in our garden sound happy though... Nick Finnis mentioned Isentropic Lift. Well, I interpret that as likely to go either way: up/down, in or out, storm or no storm. ( ) Meanwhile the weekend forecast looks better except for one thing....
  25. 4 points
  26. 4 points
    Hasn’t gone yet, might not be sunny but still sweaty heat here still waiting for the elusive storm, just hung out some washing, so that should make the heavens open
  27. 4 points
    Lol May be, but no one can blame me, voted remain.
  28. 4 points
    I'm not sure I agree mate.. I don't think the models have come to grasps with the current situation right now. We are living in unprecedented times don't forget. And as tams would say its the background drivers that lead the models, and those drivers are a little out of soughts right now. I would agree its becoming more changeable over the coming days, but I feel perhaps things will Improve towards the end of the month and 1st part of September! And let's not forget there is still plenty of time for some decent Heat to manifest. If I'm proven wrong mate I will send some Champagne your way, and likewise you can return the favour...
  29. 4 points
    Made the mistake of doing dusting n polishing around the home, within 5 minutes absolutely soaked through, surely that can’t be normal! Checked obs station, only 20c, but 94% humidity, that explains the puddle I’ve turned into
  30. 4 points
    It would be nice now to actually have a week of SUNNY high pressure nationwide with temps in the 23-27C range and pleasant nights.
  31. 4 points
    For me it's an 11/10 this is a once in a century type thing going on up here. Though well 'pay' for it by being 'storm starved' for another 10+ years, like the precious 10+ years or so (Which is generally the norm for us up here, we usually have to watch everyone on the South and East having all the 'fun' )
  32. 4 points
    Light rain and very dark here. It's still very warn and stuffy in the flat after days of heat. I can't believe I'm saying this - but I hope we don't get any storms tonight. It was hard to sleep in the heat and the last thunder was at about 1.30am last night, so I'd take a decent nights sleep over any weather extremes at the moment. But - what a storm. Lightning every 2 seconds and torrential rain. I hope it's someone else's turn tonight. I see we have a double thunderstorm warning for Saturday here - a general one and a more specific local one. Might not make any plans for Saturday.
  33. 4 points
    And killing them in a pretty horrendous way. Nice. Try and have a bit more humanity at least. Spiders are useful.
  34. 4 points
    Yes Mushy.. Looks pretty unsettled for the the next 10 day's or so... Last night's EC46 agrees with your thinking as well... Definitely signs of a marked improvement come the Bank Holiday, with a High Pressure extending from the SW to bring dare I say it... A warm and fine Holiday period... Fingers crossed.
  35. 4 points
    I'm saving that rainfall total chart for posterity, west central Scotland forecast to be the driest place in the UK over the next 10 days. Unheard of
  36. 4 points
  37. 4 points
    Normally in the UK, plumes are ended with destabilisation coming up from the south, to me this looks like destabilisation from the E which is a strange thing to see
  38. 4 points
  39. 4 points
    A fair bit of lightning going on up here just N of Bristol with distant rumbles Didn't expect this to be honest!
  40. 4 points
    Lovely storm! Just a couple of miles off a direct hit but very impressive
  41. 3 points
    Didn't realise it was gone, it might be cloudy, but I'm still hot and sweaty. Getting fed up with it now, where's the freshness gone.
  42. 3 points
    Very peculiar day today, air temperature must be flirting with the dew point somewhat as at certain times it feels cool then suddenly I burst into a sweat - and no I’m not old enough to be having flushes of any kind
  43. 3 points
    I can report very heavy rain, finally something has moved south of the river without loosing intensity. Now torrential, gaining in intensity, but no thunder...yet.
  44. 3 points
    I'd place a bet on nothing happening other than some rain for the south of London to the coast. The trough is sinking south but there's simply no energy in it. And nothing but thick cloud south of it.
  45. 3 points
    Another heatwave passes and another pathetic end convectively speaking down here. Don't seem to be able to buy more than weakening storm that staggers towards Bournemouth and then falls apart irrespective of which direction is comes from, south, east, north or west always the same results. Its a very IMBY post obviously and appreciate many have filled their boots this week, not to mention they were also the same locations that generally had multiple rounds TS activity in June. In fact drawing a line up from Central London to Liverpool and 50 miles either side it looks like it been borderline a terrific summer for storms.
  46. 3 points
    The good news is that the models are looking more promising from tomorrow onwards. The slack low pressure from the south is going to deepen slightly and start moving slowly north. We just have today to get through.
  47. 3 points
    it is going nuts in Holland on real lighting maps
  48. 3 points
    I doubt we will ever see the likes of 46 47 62 63 again how ever I hope I hope I am proven wrong and we see winter like that again.
  49. 3 points
    Stevenage copped it yesterday morning and then again tonight for about 5 six hours. Rinse and repeat for a third day. I'm tired its hard for a brontophobic
  50. 3 points
    Interestingly, the provisional mean for August 12th is 24.2C. This is only the 4th August CET day on record to be 24C or more, and a record for the date by 1.6C. It also pushes out the latest date that a day with an average of 24C or more has been record out by 9 days.
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