Ian Fergusson

Yes. Worrying - also somewhat for Madeira, incidentally. Arpege paints an equally unfunnny story from this rapid cyclogenesis, albeit with the track more SE than UKMO-GM and more progressive; landfall by 00z Sunday near the Mouth of the Loire and tracking inland across N France towards Belgium. Both models, however, are suggestive of 70+kt swathe through parts of northern/NW France midday Sunday (GM has some of this core of level 6 max gusts near Paris). Incidentally - the continued track disparity, plus ramifications regionally for us here in Blighty re rainfall totals / flood risk, wind potential and also snowfall (e.g., raw GM suggests transient late Sunday totals from 2-6cm parts of SW Midlands, Glos, and Wales etc) is the reason why UKMO Ops Centre is still holding fire on issuing the advisories / warnings. It's not that they're ignoring it(!): they want to be prudent and see if the currently good UKMO-GM continuity on track surpasses any wobbles emerging with Arpege / GFS et al.

Hmmm. Well, irrespective of any snow risk fanaticism, the Sunday rapid cyclogenesis / Shapiro-Keyser event would be already enough, you would think, to keep any forum happy - it could be very nasty for NW Europe. Impact on Madeira, NW Iberia, NW France (let alone whatever it does here) could be very newsworthy. I've updated the blog on this - pls note UKMO lack of advisories is for a good reason at present (i.e., for Sunday - not this evening, which is gonna become decidely wet down south!).

Clearly the finer details of track disparity remain an issue for now, but there's sufficient concern (based on collective evidence, not solely UKMO-GM runs, which look ominous enough) that the MO has now advised F&CO on severe weather potential for various parts of NW Europe (NW Iberia - and of course, Madeira - obviously in the crosshairs but they're not alone). This is all obviously irrespective of the eventual UK outcome.

Ah, but do they also do a line in BBQ Summers? ;-)

At least it will be mild.........

Yup, that's the broad plan, but snow might be a tad reluctant to depart the Forest of Dean quite so readily in favour of rain. Snow over Exmoor / Quantocks and probably Mendips will be a transient feature this morning / early afternoon. Tomorrow's gig will be rain; ditto rest of the working week (looks truly dire for Thurs/Fri and warnings likely to be issued). Weekend snow threat is further north based on current ensembles but it's irrelevant: potential for some noteworthy weather anyway into Sunday; the latest UK-GM just received looks very wild; and as the UKMO Ops Centre folks note to us: "There remains a large spread in deterministic and EPS output regarding intensity, track and timing of major low moving towards the UK from the S/SW this weekend, largely because this system is yet to form and originates from an area well south of ’more traditional’ breeding grounds for major lows (it originates as a kind of triple point wave ESE of Florida later today/early tomorrow and tracks towards the Canary Islands before turning North late this week)." Could be very interesting indeed....

It became every bit the nowcast issue we expected based on the 00z NAE we started the morning forecasts with and for the 0600z update, we were catering for the colder 'backwash' across much of Somerset and Wilts albeit not really relevant for our forecast purposes (not significant / disruptive snow - that was always signalled, correctly, for NE Glos and NE Wilts). Tomorrow is effectively a wet one for most (WBFL's will be above 1000m by mid afternoon across much of our region.... phew, scorchio) BUT do note the geographic caveats outlined on my blog based on the very latest UKMO assessment. Still a snow chance for some of you, but it's not a widespread one at levels <100m AMSL. PS pls note blog was updated a few mins ago

Duly done, but off to bed now so cannot offer thoughts on our impending NAE briefing - will next see it all at 4am, sorry! I suspect it will be broadly similar. Looks like your region will see all manner of snow threat at differing times this week, including tomorrow but also Tues and onwards.. Best, Ian

Graphics are updated, but please note the 'free' raw NAE output you might see on websites is not necessarily reflective of the modified (by UKMO 'human hand' at Exeter Ops Centre and again at BBC Weather Centre) frames we show on BBC. Indeed often they will be quite different in many respects. The 12z NAE run offered a slightly heavier band of snow around mid-morning through much of the SE Midlands, but the transition to 'proper' snow will be messy and we expect a widespread mix of rain/sleet/snow across a fair swathe, including down to the SE, with the PPN intensity proving very critical for allowing WBFL's to fall through evaporative cooling and allow snow penetration to the deck. The 12z is also somewhat quicker taking the main low on an ENE track across into southern North Sea, thereafter allowing a cold undercut to propogate southwards and offer a risk of sleet and / or wet snow down into Cambs, Northants, Beds and perhaps the Chilterns towards Monday evening. Let's see what the next run offers. Albeit I'll see it only at 0400 in work again tomorrow! Best, Ian PS: Ice risk tonight is the bigger concern for your region; PPS: snowfall amounts tomorrow in areas affected likely ca. 2-5cm based on NAE prog.

Ignore it - erroneous for West Country. To clarify (I just did on the 'phone with UKMO after reading this!) - Transition zone is possibly - possibly - northern parts of Glos for our region (to snow). Elsewhere, it's a rain gig. The advisory remains in force solely because of the 40% PROB delimitation but nothing more sinister than that. Incidentally, this initial weak feature running northwards at the moment (the returning, redesignated warm front) will probably bring some light snow down to 200-300m (or sleet) but either way poses a real ice risk - our major concern tonight and tomorrow. It's not to be confused with the primary PPN feature still to arrive in the morning. This is expected to offer mostly rain, albeit the latest run does enhance the snow signal somewhat for SE Midlands, not so much for us.... with that N Glos potential remaining the exception.

This comment skews the reality and needs clarifying (this does have a model thread relevance, mods!): The NAE (and UKMO-GM) output ingested into our graphics is modified at BBC Weather Centre by the UKMO Duty Forecaster before it goes on-air or to the web. These modifications, in turn, are based on (often major) tweaks made at UKMO Ops Centre by the Chief Forecaster and subsequently discussed in conference briefings held through the day / night. Moreover, those of us working regionally can make further tweaks to some elements (e.g., changing MOS temperatures to better reflect actual OBS, etc.). Thus, the raw NAE fields you might see on some websites do NOT always correspond to BBC graphical representation, because it will lack the additional 'human' tweaking of forecasters - some of which can result in quite critical changes. Clearly, to run TV graphics on just the raw NAE ingest would be quick, yes, but hardly offering the best stab at accuracy.

Actually we expect a downgrade - UKMO are revising the advisories right now and I suspect they'll be removed, with possible exception of parts of Midlands and northern districts of East Anglia. But the latest run paints this (and Wed, and Thurs events) as all rain for us.

Hi - yes, the simple answer to your question is that a number of the UKMO radar network sites are doppler enabled; a few years ago it was at least 7 sites but now it could be a good deal more. I'm not entirely sure on the current number but it's standard fare to have them as doppler these days. Ian

Please do bear in mind that so-called Precipitation Type Radar (as often available commercially) does NOT offering actual nowcast evaluation of PPN type based on radar reflectivity etc; some do so using surface OBS / METAR data to shift their emphasis accordingly (especially those available in the USA) whereas more usually, they do so by combining the current PPN alongside the output of various NWP products (typically GFS - it's free, if not always correct). Consequently, they afford merely an estimate, NOT a nowcast (until we see dual-polarised radar widely!!)..... refer to surface obs for the reality!

(but thankfully expected for that area, hence some of us are breathing a MAJOR sigh of forecast relief!! Still a snow signal for some areas of inland N Cornwall but more especially Exmoor....)

(PS, I should stress that the M4 northwards gig for snow clearly depends on the track of lows and attendant cold entrainment across their northern flanks...... don't please take it for granted, history clearly demonstrates that all manner of snowy woes can occur way SW of the M4 corridor, of course!!!)

They sure did (and you've perhaps seen the photos on my blog sent from other districts that day - amazing!!) We still have some snow in our garden in Bradley Stoke from it all. Incidentally, just updated the blog re Monday and adapted a UKMO briefing graphic on snow risk that morning.

Just ran it again (it changes the modelling each 15 mins) and it offers snow into Bude and environs quite readily from these showers. The DP's are currently down as low as -3 in some spots of Cornwall and Devon. I think some of you will see snow from these, surely.

Yes indeed so, the classic breakdown to milder scenario in some respects but with all sorts of tricky mesoscale problems for forecasters, let alone the local stuff! The M4 thing is actually quite easily explainable in many respects - from there northwards into the Midlands, you encounter the only semblance of a 'quasi continental' flavour of our island's weather in terms of a colder pool offering the sort of robustness and longevity to provide a suitable buffer and transition point against these mild, wet Atlantic incursions. Literally only a few miles makes a massive difference, as exemplified by the differences in snowfall experienced just across Glos - let alone a wider area - last Thursday. If you scaled this sort of forecasting area into, say, Tennessee, it would almost vanish. And then you get idiots saying "oh, the US forecasts are so much better". Funny that, because speak to most scientists at NOAA and they rate the UKMO's local forecasts way up in the Met premier league.

I just ran-through the night's timeline of PPN type prediction using the UKMO's high-res model; it wants to keep it as rain but changes readily to snow over Exmoor by 0100hrs (and then rain again across lowland Somerset). I'm not totally convinced the (majority) rain bias is correct; some of you could see some wintry flavour more widely, I suspect. But hey, we'll await the next set of obs.

NAE has a rain-sleet-snow combo for these tonight, with the WBFL at ca. 600m across much of thhe West Country southwards of the Mouth of the Severn, but the current DP's are low enough to offer snow across many areas. But either way, despite any temporary snow issues, it's the ice risk tonight that really grabs attention and cannot be overstated. That includes the entire SW Peninsula. Last time we saw this sort of set-up a few weeks ago in Cornwall, it resulted in a fatal coach crash. The snow risk is actually almost irrelevant for most of the SW tonight (in terms of any significant falls) albeit looks lively into the early hours for parts of Glos and north of M4 up into Oxon etc.

You'll note a broader swathe included in the advisory based on the UKMO's 12z assessment. This run called for the spread of frontal PPN overnight Sunday-Monday to be slower and the NW extent is lessened - hence the advisory re-issued. In broad terms, not a dissimilar areal focus to the events of last Thurs albeit (modified) NAE fields for 09-12z Monday are eager for somewhat more SE extention in terms of the discrimination between rain and wintry PPN; e.g., into a fair part of East Anglia, Northants, N. Oxon, etc.

Yup, it's an active mess. The snow threat for Glos (you will see on the advisory) is now back to moderate/heavy snow (up to 7cm). The longer-range stuff is clearly more than a tad challenging albeit I see our latest from the Med-Range folks at Exeter continues to talk of temps returning to around normal / milder gradually in the south, but it's a noisy story of heavy rain, possible transient snow at times and potentially strong winds along the way....

Yes, and indeed the NAE assessment suggests - in the broadest sense - a very similar geographic snow threat to the one we saw a couple of days ago - i.e., Glos / S Glos and environs now into the area for possible trouble by around 12z Monday. Note that the UKMO has re-issued the advisory on basis of last run to include a broad area of the West Country but I do stress confidence is still not great. Snow showers for many in our patch tomorrow morning still well locked-on in the new run too (more persistent snow from around N Glos up into Midlands / SE Wales). Ian

????????? Still got Spring, Summer and Autumn to enjoy!!! Think of those heady June days of TMax >25C and Spanish Plumes; or those looming Atlantic windstorms of October!! Farewell Winter - welcome all sorts of other fab weather to discuss!