Ian Fergusson

Albeit conversely, many (especially commuters) might say they're excellent for us and a major relief, frankly......

Yes, that reflects the current UKMO view and even those counties just north of the M4 (e.g., Glos, Oxon, parts of Berks, Bucks etc.) will probably be very marginal.... that's IF the current evolution proves trustworthy. Latest modified NAE output for Monday carries a rain signal across all of southern England but with the change to wintry PPN starting by ca. 06z in a line essentially from East Wales / Hereford across to Lincs and the Wash. The real midweek snow threat based on UKMO GM (and accepting - as the MO Ops Centre does - a continuing degree of disparity between models for the Wednesday event, albeit UKMO-GM and GFS are largely similar) manifests itself central Midlands northwards; e.g., GM suggestive of up to 25-29cm snowfall (!) into northern districts / northern Ireland whilst in southern England (SW quadrant especially) it's the hefty rainfall totals, plus some quite tight gradients, that catch the eye. So, lively weather for sure, even sans snow (and indeed many might say: have we not seen enough already!?). The UKMO 6-15d briefings now consistently offer the prospect of milder conditions developing across the south and the SIG snow risk being progressively excluded up into northern Scotland by the end of the period. I just photographed the first butterfly I've seen in 2010..... a biomarker of seasonal change afoot? We shall see.

Yes, the high-res modelling - even at warm bias on the run - has snow anywhere M4 northwards and on neutral / cold bias runs, snow pretty much anywhere away from the extreme coastal fringes. NAE paints 1-2cm possibly lying on cars / grass for a while through Sunday. Rest of the week looks decidedly very wet (and often windy) for us rather than snowy. Indeed with possible exception of Glos, the events looming on Mon / Wed (some uncertainty on timing re latter and continuity remains poor between models) appear to offer no threat of snow for much of southern England really; UKMO are, conversely, leaning towards severe snow potential central Midlands northwards (e.g., talk of 25-29cm snow into northern England and Northern Ireland!). For us, large rainfall accumulations will be the real story.... the longer range UKMO briefings of late are more frequently suggestive now of milder weather devloping across the south; to cite their latest (up to 15 days ahead): "....the South of the UK should be milder, with temps approaching normal at times, and any snowfall here should be short-lived. The colder air further north will be harder to shift – so the snow risk here is greater – though there is a gradual warming trend later in the period which would confine the higher risk of snow to Scotland...." Incidentally, a moment ago I just photographed the first butterfly I've seen in 2010. Lovely stuff - how much longer until we can welcome the arrival of spring-like conditions?

PS - the Monday advisory also about to be re-issued / changed because of growing uncertainty in evolution. It's all a mess really. A real forecasting headache. Am not bothering reading the Model thread stuff but for sure, nothing next week can be offered with anything better than low to moderate confidence, at least for now!

- and sure enough, the previous GM idea of the channel low for Wed is now scrubbed as a 'minority solution' according to Ops Centre and the latest evolution now looks very different indeed and far less bothersome. Given the degree of model and inter-run disparity on all this , I'm not bothering with further comment until come proper continuity appears!

Indeed so. And the Monday / Wednesday events have potential too but more especially Wednesday - I'm awaiting the next UKMO GM analysis on this one (due shortly), but the last run painted a distinctly wild story for many counties.

Eagle-eyed amongst you in S Glos / North Bristol - where it's been snowing again for around the last 15 mins - might have noticed how this continual lighter snow is quite markedly different to the intensity-dependent 'big flake' stuff earlier. This is because the WBFL has now duly dropped pretty much to the deck as expected, allowing effectively any PPN rate to come all the way down as snow here, even at low levels. Quite a reasonable covering in these parts albeit readily slush-ified.....

Note focus has always been more on Glos throughout this event - Bristol and environs always marginal, as repeatedly stressed. Glos potential, however, continues exactly as forecast (we're aware of various problems there in some districts on roads) whereas Bristol and environs on cusp of worst hit area. All depends on the pivot and 'backwash' for further Bristol snow now. It's been a very very tricky forecast of extremely small margins of error geographically, offering very sizeable differences in outcome. Given the lead time of their advisory and warning over such a rather narrow band, I think the UKMO played a blinder on this one and the NAE performed pretty well over at least 6 successive runs.

Heavy persistent snow in Bradley Stoke and environs for past 20+ mins, readily settling and urban minor roads now snow-slush cover of ca. 2cm as opposed to mere slush covered. Still time for this to get decidely tricky and especially into Glos later. WBFL's will now fall into afternoon and consequently dependency on heavier PPN rates for snow will lessen in a number of areas. Note latest blog entry on UKMO thoughts for later, cheers Ian

Latest analysis feeds the PPN fairly steadily arcing into Bristol along the M4 for a while this afternoon, still with heavier localised pulses, before the NE motion of the departing LP centre takes it all away in a less coherent (and lighter intensity) fashion. Thus our concerns for further snow risk into urban areas here for this evening rush-hour as the WBFL's pretty much drop to the deck and the PPN rate becomes less of a determining factor.... but will see what the 12Z run makes of things! Cheers - gotta dash!

It'll shift graudally eastwards and northwards as the low transfers across towards the Wash tonight. Latest NAE draws the lower WBFL 'backwash' right down through a fair part of Somerset for a while into early evening with signal for some snow appearing quite far south into the county for a little while. Probably not enough to stick really at low levels but we shall see. Snow risk transfers this eve up out of Glos into Oxon, N./ Berks, Bucks, Beds, Herts and principally northeastwards towards Lincs and Notts. Tomorrow paints rather few showers into parts of the SW with the exception of Cornwall and W Devon - many suggested here in organised bands, often wintry. A few up the Bristol Channel at times. Oh - Remember some days ago I was highlighting the 21/22nd period as one to watch? Keep eyes on Mon.....

More to come here in a while. This afternoon/evening could get a tad spicy as the PPN rotates further into the sub-200m WBFL above Bristol / B&NES and S. Glos / N Som. Note also fab scenes on Exmoor as per my last blog update. I stress orography not as important a factor in today's set-up for snow compared to PPN intensity / evaporational cooling. We've seen this already at work in the heavier convective embedded cells.

A quick interjection to stress that disruptive snow to low levels in Bristol and other areas subject to the warnings is still clearly a potential outcome - I'm not saying it's not, merely that it's not clear-cut (only 60% confidence). If anything, the snow threat increases later in the day into some of these slightly more southerly areas (Bristol, N Som, B&NES) and possibly for the evening rush-hour. We shall see. Next NAE (and high-res) run is critical.

Yes, tomorrow has all manner of potential despite continued uncertainties - UKMO about to upgrade existing advisories to early warnings (later this morning). I'll keep you updated on the blog - see initial entry on tomorrow's prospects added a short while ago.

So sorry for that - yes, boundary layer!! Apols for acronyms!! Just seen latest modified NAE issued 10 mins ago - - same story for Thurs; slightly less bullish on totals but theme sufficiently bothersome that I understand UKMO will shortly upgrade (this morning) to early warning. I guess Glos could be included but it might be a tad to the north - we shall see. I have just updated my blog with initial thoughts / details / graphic.

Actually - let me just offer a major change of NAE emphasis tomorrow - new run offers 10-20cm snow potential in a band from SE Wales across to Lincs (including Glos) and clearly has makings of a high profile event; however this major change from last NAE prog is noteworthy (it's because new run wants to depress the BL temp's further tonight).... next run awaited before UKMO decides whether to go with early warning over and above current advisory.

New modified NAE fields and DT15z high-res models offer growing confidence of a NW shift tonight/tomorrow for snow risk - e.g., consistent signal (75% of ECMWF members) going for +2mm PPN Hereford and then transferring most snow likelihood into areas >100m for East Wales / Marches into Staffs, Derbyshire, Mancs etc. Still an error margin of about 50miles or more but crucially the latest NAE is keen to keep the WBFL up at 400-600m in the frontal zone.... hence we'd expect snow at 100m+ and perhaps down to lower levels in heavier bursts of PPN. Still a very uncertain outcome all round. Latest NAE run has taken the low on Thurs somewhat further north and paints it as predominantly a rain story across the SW/West (i.e., coming into line with the GM expectation).

Maybe, albeit the latest NAE / GM variance across the SW on Thursday has led to this note of caution from UKMO: "....there are marked differences between the NAE at 12Z Thursday (which has sig snow SW England) and the GM (which has mostly rain). Confidence is thus not high enough for an advisory....." Tomorrow's NAE runs will pin it down one way or another and may re-affirm the snow potential.

I've checked our latest NAE snow prog / areal spread for tonight and the essential thrust for our region is East Glos down into parts of north Wilts and B&NES; essentially 1-2cm fairly widely signalled in these areas with spot 4cm totals in NE Glos. However, to reiterate the views of the UKMO Chief Forecaster this evening: "Timings of onset of snow remain highly dependent on precip rates, and eventual position of frontal zone is also in question. However, this is not expected to be a repeat of the type of snow events earlier this winter, with onset time and pre-existing conditions likely to generally limit the extent to which problems develop on road network." So hopefully nothing too bad / dramatic from this one...

East Cotswolds is our principal area of interest and geographically forms the rationale for extending the warning into Glos (WBFL's readily expected to fell down through 300m and snow potential aided by evaporational cooling; we're expecting for a few cm's to at settle on cars and grass (unlikely on roads to any great degree) somewhere in a swathe from north Chilterns across to east Cotswolds and environs....I do stress error margin E-W is approx 50+ miles. Thursday daytime also has some transient wet snow potential across parts of the SW / West Country based on latest NAE. Ian.

LOL Paul - my younger brother is a pilot with American Airlines based in Dallas (for over 10 years); my other relatives are in Nashville; so I've seen a fair bit of the 'amusement value' from local storms albeit some of my brother's photos taken from the flightdeck of microbursts and supercell overshooting tops are more than enough to sell any stormchasing tours at ground-level!

An adequate summary. In my own (original) branch of science, we didn't keep sharks a secret. Indeed, they kept their secrets from us. Thankfully, given the state of (what's left of) global fisheries. But I digress, and get duly depressed.....

And as ever, she is fab. Cover all bases is the watchword, because (note previous remarks) the frontal wave and PPN intensity will prove critical with the WBFL and attendant wintry 'flavour' (or not). It's almost a nowcast gig, frankly.

I avoided - in classic PR fashion - any mention or promise of 'warm evenings', 'BBQ's' and 'chilled drinks'.

Note that I've not discounted the snow chances - - it's a lively / noisy signal into the 10-15 days UKMO prog for snow but innumerable caveats attached on a regional scale. This next stalling / waving front event tomorrow will be a forecasting headache for us in many respects (snow forecasts are rightly always left as late as possible and here's the exemplar why)..... I'm not going to be surprised if the likes of Beds, Herts, parts of Bucks, Cambs, Northants, Essex see some snow from all this but maybe a transient point of interest.... hey-ho, roll-on spring / summer and the big convective stuff! (PS even the 'warmer' outliers in our 10-15 day analyses want to offer colder air back into the UK by Day 10...... please bear this in mind)