Ian Fergusson

I'm not getting embroiled in this thread but this cannot pass without refutation. Perhaps before launching such ill-informed diatribe against three friends of mine, whose combined and individual expertise I and others greatly value as colleagues, perhaps you might read - for sake of one example - John's biography and then come back here and re-attest that he (or Matt, or Liam) "...haven't got a bloody clue". Do you really think that a 2 minute TV weathercast is a full, academic symposia-style reflection of the (outstanding) professional scientific expertise of someone like John (et al.)? One additional broader point of clarification: those of you who have actually read the quotes cited in various newsmedia sources on this story today will, I am sure, have already deduced how there is a clear and important distinction to draw between a Met Office internal HR process, versus any undertaken directly by the BBC. Ian.

Hi, that'll probably be the raw / unmodified NAE you've seen (e.g., the fields shown via WeatherOnline)..... Modified version is not far off that; i.e., 30-ish mm for Bristol / Bath / S Glos over 3 hrs between around 2200BST and 0200BST but I expect worst will be passing NE of you by 0300-0400BST, then a much better start for Monday morning after daylight. Cheers Ian

Not line convection - embedded convective strip, but not true line convection. More to come for you folks there. Not looking fun on roads.

Looks pretty wet from the UKMO radar I'm watching!!! Widespread rates over 8mm per hour and it'll show localised intensification with time. Track of heaviest PPN looks as expected. Parts of Devon, S Somerset, N Dorset, Wilts gonna get v v soaked. No SFERICS yet on the ATDNet system. But frankly, thunder irrelevant with this system.

Agree, but the 2007 MCS event resulted in fairly slow (-ish !!) fluvial flooding; this is more of a localised flash-flood problem brewing due to high rainfall totals / rates in some districts across timeframe under 3hrs.

Yup - - Because thankfully the PWS warning system needs proper deliberation and high % consensual output, including across the high-res models too (UKpp etc), with various discussion then taking place before they are ever issued.... unlike just chucking some warning gig onto private weather websites where the public backlash / post-hoc peer review will be irrelevant. Tricky job for the guys at Exeter's Ops Centre to call correctly and they do a sterling job. FLASH warnings recently issued are there because the new high-res models offer support. Cheers, Ian

Ageed re potential seriousness for many districts and we have been at pains to stress this. Latest UKMO Chief Forecaster guidance not a pretty picture. Rainfall as previously advised in my posts; slightly diminished (70 v 80mm) story for spot values but only key change is the sting jet potential transferring now to just offshore Netherlands tomorrow AM and also off southerly parts of Norfolk as opposed to Wash. Trouble expected from this one, for sure. Thankfully - somewhat - it's a nocturnal feature, as will be the Wed night and Fri night depressions, we reckon. Ian

Yeah, on balance I would. If nothing else, I'd set my alarm for around 3-ish to check it all out. But then hey, I am setting my alarm for 3-ish anyway, to get to work!! Have already put suit in car to avoid undoubted drenching around that time, althought worst will pass quickly out of Bristol by around 0400BST, so folks here won't awake to all the mayhem.... and probably wonder what the fuss was all about, albeit I'd be amazed if we haven't got some local flooding issues around the West by daybreak.... You're smack in the crosshairs for this one in Swindon.....

Not sure, but seems possible - I will try to check with Medium Range forecaster at Ops Centre.

Less so - we're keeping it as 'medium risk' zone for now re rainfall, but there's still some pretty spicy totals showing there on thhe new set of outpur graphics I've got here in front of me; e.g., UKpp accumulation from 21z tonight to same time tomorrow is circa 30-40mm for you. Winds could be a bigger feature for you however, especially around tomorrow AM rush-hour as you get the 'squeeze' on the southern flank of the depression - UKpp's 10m gust prog has widely 30kts across your district; some uplands over 40kts; ditto just offshore and through entire channel crossing lanes up to or exceeding 50kts for a while. No way they'd run ferries in that, I'd wager.

Actually, let me slightly clarify that... as I've now seen the very latest severe weather briefing from the Chief Forecaster.... his new mapping does actually take the northern edge of the swathe of heaviest / disruptive rain up to Bristol and S Glos, plus all of Somerset effectively, so it's likely you'll get a fair hosing in Weston-s-Mare. Maybe 30mm or so possible. I expect worst areas for Somerset will be around Crewkerne, Yeovil, Wincanton and NE into the borderlands with Wilts, e.g., Frome, Radstock etc.... also some of the 'flashy' catchments around Chew and environs into B&NES.

Wet but nothing extreme - - head out east down the A303 / M4 into Wilts and it'll be a totally different story by midnight onwards. I would imagine stretches of the M4 will be wholly undriveable.

Hi, Much though I'd love to share with all of you the exhaustive briefing re tonight's event from the UKMO Chief Forecaster, I can't - so let me paraphrase some key elements from his last briefing document, sent after his modifications to the 06z NAE output, etc. That run upped the rainfall totals, generating a fairly broad swathe of 30-50mm extending from SW England to around the Wash, with sub-regional peaks of 80-90mm within it. Re your comment above, the latest run and simulated ascents does show potential instability embedded in the system, with the peak WBPT values at 850hPa. Thus, the Chief F/C notes for us to "...allow for embedded thunderstorms within (the system)" As noted in my earlier post, much of the heaviest rain will fall in a fairly short period, when we're expecting 50mm possible in a corridor through the SW over 3hrs from 21z to 24z tonight. The Chief advises that we're probably going to see a widespread swathe of 20-40mm accumulation, with isolated spots attaining 80mm where there's convection within the rainband. Alongside the rainfall, the winds are again important to stress as a matter of concern; my earlier post re the sting jet potential tomorrow AM in the Wash area remains valid; more broadly, the strength of the gradients around the southern and western flanks of this depression look potentially troublesome in the latest output. Worth adding that once we're through this event, we have the temporary ridging into midweek which offers only short respite before western areas (especially) get nailed Thursday with the next deep low. BH weekend has low confidence but a further threat of heavy rain into southern England Sunday/Monday. Longer range prog from UKMO makes fascinating reading but into the 10-15d period becomes decidely tricky, due to hints of a hurricane becoming embedded into the westerly flow out in the western-central Atlantic around 40-50degN.

I'll continue with more detailed updates via the blog / Twitter, but as of this morning, the key concerns for tonight's developments are twofold - - Rain potentially reaching or exceeding 80mm in just 3hrs across some districts. Rather than offer a geographic text description, you'll note my recent Twitter post includes a pic I took showing the UKMO's UKpp high-res modelling from 21z-00z tonight. The risk areas are pretty well defined by the 32mm+ per hour PPN signal.... as emphasised in the PWS warning on the UKMO website (this warning was judged on the continuity of last 3 - 4 NAE runs, close tally from Arpege and general support from other operational centres). UKpp totals from 21z tonight to 21z Monday indicate highest broad accumulations (40 to 60+mm) in swathe running NE through South Devon, SE Somerset, N Dorset, most of Wilts, into Oxon and towards the Wash. Wind - south coast / counties turning pretty windy overnight but primary area of interest / concern is into the Wash and environs, around mid-morning tomorrow, as the rapid deepening phase peaks while the LP exits into the North Sea, yielding strongest winds on rear edge. High-res and coarser UKMO models emphasise sting jet potential, offering gusts >50kts onto Lincolnshire coastline and N Norfolk especially. The one saving grace with this system is the largely nocturnal passage of it's worst wet weather conditions. Nonethless, localised flooding surely will become an issue by morning for some areas, with some degree of disruption probable. Best Ian

Hi - indeed so, the latest (I've seen) NAE offers highest totals essentially in a swathe from Bristol up NNE into Glos and West Mids.... peak values 50mm-ish through 00z Mon over following day, but not to be taken literally.... interesting that the Arpege solution tallies (and even exceeds) NAE....

OK had a peek at the forecast ascents; looks to me like a rather stable profile in the south for the heavy PPN event so I think thundery stuff unlikely here but hey, it's frankly irrelevant in terms of the PWS (versus aviation) warning perspective anyway. Indeed, I can't recall when we last had to worry about issuing a PWS lightning warning ( = ever?)... By contrast, I've seen a number of advisories and very nifty regional charts produced from Exeter re tornadic potential in many of our UKMO briefings during noteworhy convective events over the past few years, but I guess we take the zap-bang-wallop stuff as granted!!

We had a fair few SFERICS here in the West Country, mind you (yes, that makes a change).... the thundery cell that developed south of Minehead with orographic assistance late afternoon / early evening and tracked across NW Somerset / Bristol / S Glos gave a fair dose of lightning. Have yet to look at the Sunday night / Monday AM profiles re t-storm prospects -- look a likely result, though. But frankly, it's the resultant rainfall problem that's the aspect of primary concern (and ditto with pretty much any UK thundery developments of note in any case..... as tragically epitomised by Lynmouth, `52!)

Re- Sunday night / Monday - For those following this interesting development, note my comments at http://bbc.co.uk/ianfergusson Will update it tomorrow based on latest (UKMO's Chief Forecaster modified) NAE output and EC's EPS etc. Best Ian

Chief Forecaster guidance from the MetO this morning highlights the huge MCS / supercell (his opinion) forming later today across the low countries. It'll give rain into eastern England but the primary action will remain over on the near continent - it will get wild there.

Hi folks I've been drenched over on Exmoor and in Lynmouth today, interviewing a survivor / witness to the Aug. 1952 flood disaster. What an astonishing and sobering story. The real power of thunderstorms unleashed....terrifying. Anyway, for those of you storm fans in Bristol, Glos, Wilts and Somerset, your input is keenly sought - - See details at http://www.bbc.co.uk...r-best-ph.shtml All the best Ian

Hi Jackone, Yup - Broad agreement, fyi, from UKMO-GM (plus ECM) perspective (i.e. looks dry and settled for the most part - yes, there's a Glasto rarity). A chance of very warm (even hot? i.e., 27C+) temps by the weekend; at least across into the SE and quite possibly into east Somerset too.... also still the potential for some showers / t-storms locally into late Sat / Sun given localised destabilisation / sea breeze convergence effects way beyond the resolution at this range of the various NWP products. We'll see. Main recent area of model divergence has been the evolution for Friday with that LP skirting up to the NW. But better agreement presently to hold it off that way. I'll dip into the next run of ECM's precip output and see if it varies. Glasto forecast blog went up earlier today at http://www.bbc.co.uk...2010-weat.shtml albeit I'm equally focused on blogging re Valencia prospects for the next F1-GP... one head in two places!! Ian

Brief note for those of you in my region (West Country, especially parts of Glos, Wilts, W/S Som) - - our very latest UKMO high-res modelling (UK-PP) and NAE assessment from the very nice Chief Forecaster at Exeter continues the theme I emphasised for y'all yesterday re Tuesday's potential.... some potent deep convection from early morning onwards; tending to wane later through the day so I'm expecting the most vigorous 'action' to be largely earlier as opposed to later in the day. T-storms with hail expected and this is well signalled in simulated profiles. Clearly, not all districts will see the heaviest downpours, but the current UKMO Advisory says enough regarding the regional thrust of things.... off to bed now; up at 0255 for early shift! And I'm genuinely delighted! Ian

Yes, fantastic Arcus cloud (shelf cloud) formed by the t-storm outflow. You need to keep this shot - not often seen so vividly in the UK; it's a good one - I'd defo use it here on BBC TV weather.

In the widest sense, no - indeed quite the opposite, as the ridging from the west kills most of 'em off this evening. Most.... Because, some will continue into tomorrow AM, fuelled through the thermal plumes of the old occlusion. As we then see Monday's over-running system arrive, it's some convergence-driven areas that will become noteworthy for deeper convection: The first of these through the NW / Yorks / down towards Lincs and the Wash and Norfolk (this northern area focused by hydrostatically-driven convergence along the graveyard occlusion plume); the second, further to the SW, then aligned roughly from the Bristol / SE Wales area, down towards S'Hampton. Profiles suggest that in any case, CAPE will be more limited than today; showers somewhat less frequent (versus the more widespread dynamic and at times heavy PPN) and we expect lightning to be less prevalent generally. Conversely, some of the PPN rates could be rather eye-catching and lead to FLASH warnings locally, especially in that more northern area I mentioned.