91Èȱ¬

UPDATE 10:30HRS, SUNDAY 31 JAN. 2010:
Good morning! The grey skies above Bristol reflect the forecast developmentsÌýI described yesterday - and in many respects, little has changed in terms of our expectations today.

Some areas are still likely to see a dusting of snow - anywhere up to 1cm typically - spreading down from Wales into parts of southern-central England and probably across to the likes of Bucks, Beds and Herts.

A chance of some localised heavier snow exists; primarily however,Ìýtoday's feature is oneÌýof (indeed, giving only sleet and perhaps justÌýrain for some, but mostly it'll offerÌýsnow). There will be pockets of - perhaps even someÌýCumulonimbus cells - offering heavier snowfall rates in a few areas, mostly up towards the NW of the swatheÌýaffected.

I've added below the Met Office's high resolution (1.5km) prognosis from early this morning,Ìýsuggesting the areas most likely to be seeing / have seenÌýsome precipitation by around 6pm this evening.Ìý Note the colour key on the left and the green signal (rain or sleet) around some Bristol ChannelÌýcoastal areas, parts of Somerset, SW Wales etc. The inland signal is also a mixed rain-snow combination albeit we think the model might be overplaying the 'wet' emphasis a tad too much. This Met Office product only shows the type of expected precipitation, not the intensity or accumulations...

Either way, it'll probably prove a patchy and mostly light spell of precipitation for most of our districts affected - notably parts ofÌýGloucestershire and north Wiltshire.Ìý

UPDATE 21:30HRS, SATURDAY 30 JAN. 2010:
Note (below) some key differences in the very latest NAE modelling for tomorrow, not least the later and somewhat more restrictive spread of snow showers.Ìý The essential theme and driving force (a weak baroclinic zone, see earlier entry) remains the same, however.

Worth adding that the raw NAE is very keen to show most of these showers as liquid precipitation (rain / sleet mix) rather than snow, but the Met Office 'human' view holds the opinionÌýthatÌýmany of these will appear as snow inland.

Nonethless, this later arrival of the showersÌýinto (northern) parts of our region is very critical: the precipitation rates are mostly rather light in any case; the daytime maxima will have just occurred and and the Wet Bulb Freezing Level is generally over 200m... so, will we see much snow?

Well, high into the cloud tops forming over parts of the Midlands and Gloucestershire, the temperatureÌýcould be around -20C and we could still see snowfall boosted - through convective processes -ÌýtoÌýoffer a dusting up to 1cm beneath the broader span of cloud cover and locally accumulating to around 3-6cm.

UPDATE, 19:15HRS, SATURDAY 30 JAN. 2010:
At this rate, I will need to start a new blog entry!Ìý But meanwhile, please bear with me...

My last update discussed tomorrow's prospects andÌýhere's some further thoughts, based on the latest from the Met Office.

The general thrust remainsÌýlargely similar: i.e., snow showers spreading east during Sunday morning, with generally light accumulations for mostÌýdistricts eastwards of the Severn.

In many respects - and I do stress this - the risk of ice remains our major concern, NOT the expected (mostly, but not wholly, small-ish) volumes of snow. Yes, there will be local exceptions, inevitably, but hopefully I've made the point!

So what is going on?

Upper air activity - in this case, an upper ( if you are into the detail!)Ìýtrough - will descend southeast from around the NW of Greenland on the cold (northerly) side of the prevailing jetstream. Eventually, it will comeÌýtogether with the being caused by an upper ridge (of higher pressure) creeping eastwards on the cold side of the jetstreamÌýand steadilyÌýsqueezing a . Does it sound like complex atmospheric physics?ÌýOh, yes...Ìý

So, do spare a thought for the Met Office scientists interpreting all this in ExeterÌýand trying to get your local forecasts spot-on...!

The end result, however,Ìýis a forecastÌýwe expectÌýwill differ - for some, quite markedly soÌý- from the original notion (as you likely sawÌýbroadcast a day or two ago)Ìýof a 'crisp, blue-sky'Ìýsort of Sunday.

Yes, many parts of the UK will have exactly that; but for some us in the West Country, it will surely prove a much more mixed (and cloudier)Ìýset of fortunes....

I've added below the latest Met Office (NAE)Ìýmodelling of wintry shower progression eastwards into the morning but also, note the high-resolution (4km modelling) prognosis graphic following thereafter, suggestingÌýeventual snow depths from midnight through to 21.00hrs on Sunday.....

It's hardly anything truly spectacular, is it?. Which brings me back to my original point about a broaderÌýice risk, rather than loads of snow!Ìý But locally, there will be a good deal of variance in the amount of snow you could see lying.

UPDATE: 11:45HRS, SATURDAY 30 JAN. 2010:
So far, so good with the forecast handling of the this morning's weather - we'llÌýsee a continuation of snow showers feeding down off the Irish SeaÌýinto North Cornwall through the day, but otherwise it's looking totally glorious everywhere.

The latest Met Office modelling for Sunday throws-up some potential complications to muddy an otherwiseÌýdry-sunny-cold story.

We'll be keeping an eye on developments during the morning,Ìýextending from the northwest (caused by a partially , if you are interested in the technical reasons behind it!). The upshot is likely to come in the form of snow showers, giving light to moderate accumulations across from Wales and into parts of central-southern England; some extending perhaps as far east as some of the 91Èȱ¬ Counties.

Below, the latest run of the Met Office's NAE (North Atlantic Evolution) - as tweaked by their Chief Forecaster at Exeter - gives an idea of how these showers could spread steadily eastwards tomorrow towards midday. It'll be fascinating to see how this element of the forecast develops in successive runs of the Met Office supercomputer.

Ìý UPDATE: 18:40HRS, FRIDAY 29 JAN 2010:

In case you wondered why I've been so keen (effectively over nearly 3 days of local radio and TV broadcast forecasts as well as here on the blog!) to talk-up the chance of snow showers affecting parts of West Somerset / Exmoor and perhaps as far east as the M5 during tonight and tomorrow morning, I've included a graphic, below, to stress the point.Ìý

This is the Met Office's high-resolution prediction for accumulated precipitation during the early hours of Saturday morning (1am-7am) and you'll notice the signal for a stream of showers to extend southwards into parts of the SW Peninsula off the Irish Sea (note, incidentally, the far more potent snow risk along NE coastal counties and into East Anglia).

As I write, we're now watching the predictedÌýIrish SeaÌýfeature forming on radar. For a while overnight, we suspectÌýsnow showersÌýcould brush just a tadÌýfurther eastwards from Exmoor & environs, perhaps extendingÌýto the likes of Burnham-on-Sea, Weston-super-Mare and even Bristol, which is why I've used the M5 corridor as a rough guide.... i.e., in the broadest sense,Ìýdistricts west of it within SomersetÌýare most likely to see some snow showers tonight.

Up over Exmoor, we might even see accumulations close to 10cm in some spots by the end of Saturday.

UPDATE: 15:45HRS, FRIDAY 29 JAN. 2010:

The showers shown just north of Monmouth in the radar image below just reached me here in Bradley Stoke, South Gloucestershire.Ìý You might remember a blog I wrote about how to visually spot hail falling. It's a similar story for spotting snowfall from showers - I've taken a photo (below) to make the point visually. Those billowing white areas beneath the cloudbase are areas of snow actually falling - still about 1,000ft up at this stage but within about 2 minutes of taking the image, snow began falling steadily.... and still is.ÌýÌý But as I mentioned in my blog this morning, these showers are blowing-along quickly and so (for most areas - Exmoor excluded)Ìýany accumulation from snow, graupel or hail will prove a temporary point of interest!

UPDATE: 15:15HRS,ÌýFRIDAY 29 JAN. 2010:
As per the forecast detail offered in my original blog (see below), this afternoon's crop of wintry showers have started appearing into the West CountryÌýessentially on-cue. The Met Office model runs since yesterday lunchtimeÌýhad called for these to appear from around 3pm - not bad accuracy!Ìý Recent distribution of these is shown in the rainfal radar image below. They'll continue sinking southwardsÌýfor a while this afternoon and turn increasingly more to a sleet-snow / snow emphasis as the Wet Bulb Freezing Level continues to drop further...

(ORIGINAL BLOG ENTRY FOLLOWS)

Remember February 2009?ÌýÌý

It's by no means impossibleÌýthat we'llÌýsee similar weather establishing across the same parts of the UK in a week or so.... and possibly more widely, too.

Usually, IÌýrestrict my blog to matters of forecast interest within a few days of the here-and-now, but the growing signs - and growing forecast model consensus - signalling a return to much colder conditions by the end of next weekÌýdeserves an early mention. More on all this in a moment...Ìý

Bristol's Kellaway Avenue - along with much of the south of England -Ìýwas almost impassable on this morning in February 2009. Colder weather set to return later next weekÌýcould offer a repeat performance... at least for some parts of the country (Photo: Ian Fergusson)

For the time being, we'll also see colder conditions set-in through today, courtesy of a northerlyÌýflow and a pronounced windchill developing into the weekend. It'll take a little while during today (Friday) for this to become truly apparent here in the West Country; the overnightÌýrain and cloud is already departing off to the south and behind it, the colder conditions are just starting to descend readily from the north, bringing the Wet Bulb Freezing Level (refer to this blog for details) steadily down towards ground level this afternoon.

We're anticipating a period into the mid-afternoon when a secondary feature running southwards (a trough) could just pep-up some wintry showers forÌýaÌýfewÌýdistricts - especially parts of east Gloucestershire and north Wiltshire - so don't be surprised if you see some temporary (not disruptive, I stress!)Ìýsnowfall from these as they pass quickly by on the brisk, chilly breeze later today.

By this evening however, for most across our regionÌýwe're intoÌýa noticeably raw, starry-sky dryÌýnight to come, as temperaturesÌýdrop to around -2 to -4C in and around the likes of Bristol, Bath & Gloucester's urban areas, accompanied by a significant windchill.Ìý

Out in West Somerset (and especially up on Exmoor), you could catch some snow showers feeding southwards off the Irish Sea - indeed, the risk of these will continue for your districts throughout the weekend and I'd not be surprised if we see a reasonable accumulation of snow up on parts of Exmoor by the time we reach Sunday.

For the rest of us, especially anywhere east of the M5 corridor, much of the weekend looks bright,Ìýdry (bar the odd snow shower) and certainly feeling cold, with widespread overnight frosts.

So, onto next week's developments....

The week actually starts with a temporary return to something a tad milder.

B y Tuesday, we expect a spell of fairly widespread rain - with hill snow on it's leading edge, tracking eastwards -Ìýbehind which,Ìýtemperatures will peak somewhere around the seasonal average. But thereafter, the trend is one for cold anticylonic weather to steadily exert itself across theÌýcountry andÌýinto the second part of the week, a return to something a good deal colder will become apparent pretty much everywhere, with the exception of the far West and NW.

ÌýBetween Friday and Sunday, developments are expected to yield a bitterly coldÌýeasterly flow off the continent, bringing the risk of snowfall - some potentially heavy - into parts of the SE initially, with a chance of this spreading further westwards to affect other areas. And beyond that, the south-easterly flow could well be replaced by a east-to-northeasterly version, thereby continuing to offer a growing risk of further snow.

Incidentally, if you're seeking to understandÌýthe detailed technicalÌýmatters behind longer-range weather modelling and indeed climatology, it's well worth dipping into (Paul is the weathermanÌýat 91Èȱ¬ Look North based in Leeds).

It's not impossible that we could see a synoptic set-up not dissimilar to the one of February 2009. It's all farÌýaway time-wise, of course, and much could (and doubtless will) change... but for sure, some very interesting - and surely very cold -Ìýweather lies ahead for the first half of February 2010...

UPDATE, 06.15HRS, WEDNESDAY 27 JAN. 2010:

Much as expected, the latest Met Office modelling continues to suggest a minimal risk of any snow for the West Country from Thursday overnight into Friday. Thus, myÌýcomments belowÌýfor this to be a largely (or wholly) wet - rather than white - event for our regionÌýremain valid.

The latest models are still keen to develop a convergence zone early on Saturday descending southwards from the Irish Sea into SW England (again, see original thoughts on this below).

Our expectation is for showers from this featureÌýto fall as snow anywhere above 100m inland from the north coasts of Cornwall, Devon and parts of West Somerset - notably over Exmoor. Given the direction of prevailing flow, I think it's very unlikely for showers to extend any further eastwards to affectÌýother parts of our region. Worth stressing that icy roadsÌýcould be a far bigger issue across parts of the SW Peninsula affected by these showers, rather than any actual accumulations of snow.

The weekend continues to shape-up as largely bright and dry, with a quite significant NNW breeze at times making things feel decidely chilly. The cold weather continues into next week too, with growing signs of another cold (perhaps very cold) easterly flow establishing once again.Ìý Ice scrapers at the ready....

Ìý

(ORIGINAL BLOG ENTRY FOLLOWS, TUES. 26 JAN. 2010)

In my last blog, I briefly alluded to developments later this week, with a potential for further snowfall across parts of the British Isles later on Thursday and into Friday.

So let's start by also adding Saturday to the broaderÌýperiod of interest. More on that in a moment.

For the time being, the essential theme is one of colder air establishingÌýon a northerly flow across the country progressively through Thursday and into Friday. And later on Thursday, we'll watch an Atlantic system -Ìýcombined withÌýa set of highly complex atmospheric variables and a 'wave-like'ÌýdisturbanceÌý- yield a risk of snow for some parts of England overnight into Friday.

I stress some.

It's a set-upÌýunlike any of the 'snowy synoptics' seen so far this year. For us in the West Country, the impact currently remains very tricky to call, so I've been suitably circumspect on our TV and radio broadcasts.

I'm largelyÌýinclined to downplay this one, if I'm honest. My first stab - with the usual forecast caveat that things could change (inevitably, in my profession!) -Ìýis for this Thursday-Friday evolution to yield a small snow risk for most (if not all)Ìýof us across the region.

Indeed the latest Met Office modelling is increasingly paintingÌýthe greatest snow potential out across northeast and central-eastern England, with a broader swathe of rain and sleet the more probable resultÌýacross most of our area.

Nonetheless, there's still a great deal of uncertainty, not least on the exact track of this feature as it sinks southeastwards late on Thursday. So, until the Met Office sees better continuity in model output, it'll wisely hold-off issuing any sort of public advisory until confidence improves regarding the regional bias of possible disruptive impacts.Ìý

The real forecast headache forÌýme and my colleaguesÌýcomes as this featureÌýdrops away southeastwards into Friday morning.

As it does, the northeasterly (rear)Ìýflank of precipitation, steadily pulling in colder air, will readily lower the Wet Bulb Freezing Level (WBFL, see explanation containedÌýin this blog here) down to around 200 metres or so... offering a greater chance of (wet) snow.

I've attached hereÌýtwo Met Office graphics belowÌý-Ìýmany of you who read my blogÌýwill now be familiar with these and how to interpret the WBFL contours and precipitation symbols.

You'll note (above) how by midnight into Friday,Ìýthe crucial blue sectors lie muchÌýfurther to the east andÌýnortheast in these frames, suggesting the snow risk will lie further off in those regions.

ÌýHowever, as the rain/sleetÌýmoves southwards - indicated by the midday Friday graphic (above)Ìý- we could still see a spell of transient snowfall into some of our districts, rather akin to the short-lived but partially disruptive experiences ofÌýlast week in the likes of Gloucestershire and Wiltshire. Also, any rainfallÌýprior toÌýa transition to snow could wash salt off the roads, increasing the risk of an early ice problem, depending on the timing of this feature slippingÌýaway to the south during Friday morning.

Now, perhaps of greater regional interest for usÌýis during earlyÌýSaturday, when - with a distinctly cold northerly flow blowing across us all - we're watching for a set of factors toÌýcombineÌýand feedÌýa succession of snow showers, plus merged areas of precipitation,Ìýinto parts of the southwest off the Irish Sea. Shown on theÌýright here is how the Met Office's Global Model offers a first stab at this possible development by the start of Saturday.

It's through a process termed a and the Met Office modelling is suggesting a fair swathe of snowÌýpotentially establishing east-southeastwards off the Irish Sea and extending down into parts of the SW Peninsula.

But that's still a long way off... I'll keep you updated on the latest forecast thoughts, as ever. It's shaping-up to be an interestingÌýspell of weather for us by the weekend; for sure, a distinctly cold-feeling one -Ìýif not necessarily aÌýguaranteed snowy one!

Ìý

I'm very grateful to local microlight pilot Steve Slade, who has sent me some spectacular photos taken above the River Severn in Gloucestershire.

You might have seen some of Steve's aerial imagesÌýof our regionÌýon 91Èȱ¬ Points West weather bulletins - I tend to use them quite regularly on-air (see here for instructions how to send photos to us).

On Sunday (24 January), Steve flew his microlight above the just west of Gloucester, taking a series of photos showing just how the mighty riverÌýhas spread out across a fairly broad rural area.

Of course, there's been a large volume of water accumulating in the catchment over recent days, thanks to a combination of melting snow and some spells of rain. The net result - not least from many smaller streams andÌýbrooks bursting their banks too -Ìýis very clear from Steve's pictures. Thankfully, the flooding has been a fairly slow process without any impact on major urban areas.

However, you can see various farms and smaller rural hamlets have become almost encircled by the rising waters - if you are reading this from any of the affected areas, do share your experiences here on the blog. With a largely dry spell of weatherÌýbetween now and late Wednesday,ÌýI'd imagineÌýthe situationÌýwill gradually ease, but I'll be interested to hear the expert views of any hydrologists out there!

If you have concerns about flood risk, the is always at hand and regularly updated with the status of every river, stream and brook, no matter how small.

Later this week, we will again seeÌýa cold northerly influence re-assert itself across the British Isles, bringing the risk - albeit currently very uncertain - of some rain, sleet and snow descending southeastwards into parts of the West Country later on Thursday and into Friday.

It's a complex weather set-up into that period and quite different to the that brought us snowfall on the past three occasions. I'll keep you up-to-date with our evolving forecasting thoughts here on the blog.

Ìý

UPDATE, 09:30hrs, WEDNESDAY 20 JANUARY:

The Met Office warnings proved very timely and accurate for this one. It's usually at this stage us weatherfolk breath a collective sigh of relief, but it's hardly a 'relief' for those people trying to get to work this morning...

Visibility during the rush-hour on stretches ofÌýthe M4 between Bristol and ChippenhamÌýhas been described as "terrible" due to fast-falling snow, with reports of it settling fairly readily in some areas (such as Swindon and elsewhere in north Wiltshire).

It's a very similar story up the M5 through Gloucestershire, with a good deal of snow falling there and settling steadily away from the major road surfaces.

That oh-so-tricky-to-forecast transitional boundary - where snow is falling and starting to settle, as opposed to more a rain-sleet-snow mix - seems to be lying somewhere just south of Bristol,Ìýjudging by Highways Agency live traffic cameras. Snow has been settling too - patchily, at least -Ìýinto parts of Bath & NE Somerset, towards the Wiltshire border. The regional thrust of the forecast was pretty close to the reality; now we need to await just how much snow actually falls. I'm seeing little sign of any significant settling until moving north and north-east of Bristol, as per expectations.

The Met Office rainfall radar image, snapped at 09.15hrs (below), shows the dual-banded nature of this system developing and the fairly broad swathe of precipitation falling across much of southern England. We expect those two bands to merge today, become largely stationary and then weaken effectively in-situ as the forcing aloft eases awayÌýboth northwards and offÌýinto NE France. Our current expectation is for some snow to still fall across parts of Gloucestershire and Wiltshire even by mid afternoon, so any clearance will be slow and characterised by the snow rates getting steadily lighter, patchier and resorting to rain-sleet as the day progresses, as opposed to skies suddenly clearing.

The Gloucestershire/central-North Wiltshire emphasis still looks a solid bet for the heaviestÌýof the snowfall.Ìý Please do keep your reports coming and post them here on the blog!

Ìý

UPDATE, 22:15hrs, TUESDAY 19 JANUARY:

My final thoughts, having seen the latest Met Office modelling...

The frontal progress will prove slightly ahead of original expections - thus any snow risk effectively expectedÌýbetween around 0800 and 1200hrs tomorrow.

TheÌýnotion of snow - noteworthy totals, at least - beingÌýlargely restricted to Gloucestershire and parts of Wiltshire remains steadfast. So, I'm sticking to my original comments on this (doubtless to be proven wrong?).

Indeed, I'll suggest further refinement to this theme: effectively NE GloucestershireÌýand extreme north/upland north Wiltshire most likely to see snow (i.e., if taken from all the West Country districts) and even in those areas, rather patchy in terms of amounts.Ìý

And in any case, it'll all be replaced by heavy rain and strong winds by Thursday!Ìý Far easier to forecast....

Ìý

UPDATE, 19:55hrs, TUESDAY 19 JANUARY:

I've beenÌývery impressed how the Met Office modelling has retained bothÌýcontinuity and the regional essence of this forecast ever since I started penning this blogÌýentry.

Other forecast models are now catching up with the general theme, albeit - as earlier noted - the French versionÌýhas offered support for a while. So now, we await reality.

Below isÌýthe latest Met Office prognosis for likely snowfall distribution and amounts. Blur the edges, please, but it does make interesting comparison with the chart I reproduced hereÌýon Monday. The broad theme remains largely similar.

Incidentally, we expect road surface temperatures (RST's) will not fall sufficiently tomorrowÌýfor snow to settle widely or for any prolonged timeÌýon most roads, other than where the rates of snowfall are greatest.

Settling onto grass, yes.

This willÌýprove a key point in determining the level of travel / road network disruption... I'm still not expecting anything like last week's widespread scenes of snowbound chaos, but there will be local exceptions, for sure.

UPDATE 13.00hrs, TUESDAY 19 JANUARY:

My last update explained - as simply as possible - how the Wet Bulb Freezing Level (WBFL) plays a critical role in our snow forecasting. If you've read that, then the chart below will (hopefully) make some sense...

It's again from the Met Office and continuing to tell a largely similar story to their last forecast output; i.e., rain turning progressively to snow during tomorrow morning as it moves northeastÌýand especially towards midday.

Shown here - superimposed against those all-important WBFL contours in greens and blues -isÌýwhere the signal for rain (green) versus sleet and snow (blue) is expected to occur by midday tomorrow.

Note again howÌýthe geographical emphasis by this timeframeÌýisÌýprimarily on SE Wales, the SW Midlands and parts of southern-central England. If anything, we're leaning towards a slightly further NE focus, such that Birmingham and environs (including Oxfordshire)Ìýcould well see up to around 5cm of snow through tomorrow.

I still stick to the notionÌýof upland Gloucestershire and upland Wiltshire seeing most ofÌýany West Country snow angle to this. Below around 100m above sea level,ÌýI wouldn't be at all surprised if we see only rain and sleet -Ìýperhaps mixed with some very transient snow -Ìýin the likes of Bristol, Bath and most ofÌýSomerset.

With rain turning to snow above about 300mÌýover Wales early in the morning,Ìýwe expect it toÌýform a cold 'pool' of air at lower levels in adjacent Gloucestershire through evaporative cooling (the latent heat exchange process...remember this fromÌýmyÌýlast update?). This shouldÌýhelp the WBFL to drop - progressivelyÌýthen aided by colder air advecting in from the near continent later in the day.

The output I've reproducedÌýhereÌýis from the (called NAE, the North Atlantic Evolution)Ìýand has been expertly 'tweaked' in this version by the Chief Forecaster working at Exeter. This sort of detailed mapping, benefitting from hands-on modificationÌýat the Met Office and updatedÌýthroughout theÌýday, - and indeed directlyÌý'drives' the ever-changing graphical representation of rain, sleet, snow, cloud and wind you see on our TV bulletins.

Ìý

UPDATE 10:35hrs, TUESDAY 19 JANUARY:

The continuity between successive runs of the Met Office forecast models has proven exceptionally good for developments into Wednesday. Indeed our confidence is helped by the French, whose own forecasting model, called Arpege, is keeping pretty close company with the Met Office on this evolution.Ìý

The area of greatest uncertainty involves just how much snow will fall. It's unlikely to be on a par with the disruptive events of a week ago - broadly speaking, at least.

Much as expected (see my previous comments below), for many of you at lower levelsÌýthis will prove a very marginalÌýsituation with less rather then more snow likely. However, it's by no means impossible we'll see up to 10cm falling on higher ground of SE Wales and perhaps 5cm across parts of the SW Midlands, including uplands of Gloucestershire and probably across into Wiltshire and Oxfordshire.

I doubt the snow will fall or for that matter linger on the groundÌýfor very long, however. The signal for a return to sleet and rain from the west remains very solid, so a likely outcome will be rain andÌýsleet arriving at first during Wednesday morning, turning heavier and ever-more-wintry in natureÌýas it spreads northeastwards towards midday.

The period between late morning to early afternoon holds the greatest potential for seeing snow, especially as the system progresses anywhere north and east of Bristol... so I'm staying with my hunchÌýthat parts of Gloucestershire and Wiltshire have the greatest chance of snowfall exceeding, say, 2-3cm. For a while, at least...

By mid-afternoon the heaviest precipitation will have departed and lighter outbreaks of rain and sleet follow from the west. Thursday, meanwhile, still looks distinctly grim: very wet and very windy; some pretty significant weather that day, for sure, and so worth highlighting this!

For those of you interested in the science behind our forecasts, I've added a little insight belowÌýinto just how tricky snow forecasting can prove for us, not least on a sub-regional scale.

One ofÌýthe most important forecast products supplied to us by the Met Office predicts where the boundary will lie for the Wet Bulb Freezing Level (WBFL). Without overbearing youÌýon the physics, as snow falls it evaporates -Ìýby varying amounts -Ìýinto the surrounding air. The latent exhange of heat from this process cools the atmosphere and bear in mind, billions of falling flakes are all contributing to theÌýoverall effect.Ìý The WBFL, measured in metres, offers us some idea how far up the snow is theoretically likely to change to rain (e.g., 200m up, 400m up etc.) and critically, just how easily this level canÌýbe brought downwards to the surface.

This lowering of the WBFL - and thus the extent of evaporative cooling -Ìýoften occurs when the rate of snowfall intensifies sufficiently to bring colder air downwards from aloft (albeit strong winds can effectively stop the process).ÌýIf conditions are right, the WBFLÌýcomes steadilyÌýdown from,Ìýsay, 200mÌýabove your headÌýandÌýsmack to the ground, allowing snow to penetrate all the way to the surface even when your car thermometer might still show +3C.

So, heavier rates of precipitation can make a very big difference in 'marginal' situations; you may recall, for example, how some very light precipitation a couple of weekends ago barely arrived asÌýdrizzle for many of us, let alone as snow. It was a real forecasting headache and the WBFL played a critical role.

All manner of additional small-scale factors: relative humidity; windspeed; terrain; the type of cloud providing the snow - play key parts in determining if snow falls, versus sleet or rain. Tiny variations in any ofÌýthese can make the difference to a snow forecast being perceived asÌý'right' or 'wrong'!

Now, the chartÌýabove might look a scrambled mess to many, so to help you see the British Isles I've highlighted the Bristol Channel for orientation! The cluster of round circles swathed across the chart show where frontal precipitation - rain - is expected to be falling at midday on Wednesday and how heavy it will be (larger circles =Ìýheavier rain).Ìý TheÌýstar and x-like symbols in blue are a signal from the computer modelÌýfor precipitation falling as snow (again, larger stars = heavier snow). Bear in mind this is a prediction, not rainfall radar here-and-now reality, so we're always mindful not to follow such charts too slavishly!

Note how the broader shading of the WBFL valueÌýchanges from greens to blues, with the boundary lying somewhere into the likes of SE Wales and northern parts of the West Country/SW MidlandsÌý(Glos, Wilts).

The lighter blue colour startsÌýwhere the WBFL contourÌýwill be at 400m; the next darker blue at 200m. As explained above, given heavy enough rates of precipitation (which we expect for a time tomorrow),Ìýit's possible to bring the WBFL right down to the deck from these heights and so it's over in the blue side of that boundary where snow could prove the likely outcome. And adding to the overall effect will be colder air moving across from Germany, helping to lower the WBFL more widely as Wednesday progresses.

Did this make sense? Phew....!

Ìý

UPDATE 21:30hrs, MONDAY 18 JANUARY:

Here'sÌýmy first update, as promised (see original entry below).Ìý

Our Met Office partners have synthesised data from another computer run and the mapping below, courtesy of their expertise at their Exeter HQ,Ìýgives a 'best guess' (and we do stress 'best guess' at this stage!) of the likely snowfall distribution and amounts for Wednesday.

If you followed my blogs through the last two snow 'events' here in the West Country, you will have seen similar predictive graphics I'veÌýreproduced from the Met Office. In many respects, their accuracy has proven very striking and reflects on how the scientific effort behind meteorologyÌýhas evolved not only on a broadscale, but on a much smaller scale, too. And so it continues...

If you superimposed this level of geographic weather prediction onto, say, a map of the USA, the level of fine-scale forecasting accuracy we've seen this winter in the UK would prove all the more compelling.

Yes, of course we get it wrong sometimes, but then these errors will always seem so much more magnified when viewed locally across the cities, towns, villages and hamlets of theÌýcomparatively small islands we inhabit; encircled by a massive ocean on one side and a vast continent on the other.

And no - that's not an excuse for when we get things wrong; it's merely a reasonedÌýinjection of scientific reality!Ìý

I expect this to prove aÌývery marginal event in terms of any meaningful snowfall; i.e., many will see only rain or sleet in the West Country, so I'm not getting my cat's snow hopes up (refer below!) too highly....

Ìý

(ORIGINAL POST FOLLOWS)

I drove from Bristol to Hertfordshire over the weekend and it was interesting seeing the varying amounts of lying snow still left along the M4 corridor.

With milder conditions prevailingÌýsince Friday, much of the snow - as expected -Ìýhas melted to be replaced by a good deal of standing water. However, some appreciable amounts still cling to shady parts ofÌýfields and woodlandsÌýalongside the motorwayÌýin Berkshire and Wiltshire.

And a snowy top-up, not least for those very same fields and woods,ÌýisÌýforecast for mid-week...

Any fresh snowfallÌýwillÌýbe greatly appreciated byÌýmy cat, Pickle - seen here last week enjoying a 'snow leopard-wannabe' moment. But are snow-mad cats rather a rarity? I'm really not sure. Some clearly hate the stuff, avoiding putting even a paw in it!

Over the past 36 hours, the Met Office's supercomputer has been keen toÌýrepeatedly forecastÌýup to 5cm of snowfall arriving on Wednesday morning, spreading eastwards to affect some partsÌýof the Westcountry, central and eastern England - possibly including more western parts of London, too.

The Met Office has issued an advisory - .

Those of you who follow my blog regularlyÌýwill know I'm reluctant to get bogged-down in the finer-scale detail at thisÌýrelatively early stage. But suffice to say, this will prove yet another of those 'what if?' situations for much of the West Country. Some of you areÌýlikely to see a fair amount of snow and others... none.

The broad theme suggests around 1 to 3 cm of wet snow (the type we experienced last week)Ìýfalling at low levels for a while through Wednesday morning -Ìýwith 5 or more centimetres in quite a few districts -Ìýall becoming progressively lighter into the afternoon, as it moves away eastwards. The mechanism, rather as we saw last week, is courtesy of a frontÌýswinging off the Atlantic, overriding colder air lying across much of central-easternÌýBritish Isles.

The recent snow caused all manner of transport problems but whether Wednesday's forecast heralds similar levels of disruption remains to be seen. It's quite likely someÌýfurther snow will fall here - at Panshanger Aerodrome in Hertfordshire - whereÌýthe frigidÌýscenes shown here a fortnight ago have since melted awayÌý(Photo: Ian Fergusson)

And again much like last week,Ìýthe local fine-detailÌýforecastÌýaccuracy will prove a real headache. For usÌýproviding the forecasts, aÌý'win or bust' outcomeÌýis likely to involve distances of only a few miles,ÌýpredictingÌýthe transitional boundary where rain changes to sleet and then to snow.

Not easy, but we've already had two attempts at thisÌýin 2010...!

For now, it looks likeÌýdistricts from around Bristol eastwardsÌýare most likely to see some snow, but I'm expecting upland areas inÌýeast Wiltshire and east Gloucestershire to beÌýprincipally in the crosshairs for any more substantial falls. But this is speculative:Ìýlet's see what the next set of higher-resolution Met Office predictions make of things. I'll provide updates here, as ever, and look forward to reading your thoughts and opinions.

By Thursday - withÌýanother Atlantic incursion above usÌý-Ìýthe snow has been largely or whollyÌýreplaced by very wet, windy and milderÌýweather; indeed, perhaps 20 to 30mm of rain across much of the West. Heavy snow, perhaps even blizzards,ÌýisÌýa moreÌýlikely outcome up across northeastern parts of the British Isles, where the colder air remains.

Incidentally, the longer term outlook always holds a lurking -Ìýif small -Ìýrisk of the bitterly cold east/northeasterly influence returning laterÌýinto next weekÌýto 'block'Ìý any milder Atlantic weather from readily progressing across the country (as it did so effectivelyÌýa fortnight ago).

But for now, after this week'sÌýexpected snow, wind and rain clears, our broad expectation is for the West CountryÌýto experience a settled spell from Friday andÌýintoÌýweekend; withÌýfurther wet, windy and close-to-average conditions then dominating into the start of the following week. Will this become reality? We shall see!

Ìý

I barely managedÌýmyÌýjourney toÌýwork this morning. I dare say a number of you experienced similar problems?

After removing what seemed a ton of thick snow from my car at 0330hrs here in Bradley StokeÌý(at least 5cm of wet snow having fallen by then), it proved almost impossible to actually reverse onto the road.

Ten minutes later, I was breathing a major sigh of relief and tip-toeingÌýmy way around an almost deserted and decidely slipperyÌýAlmondsbury interchange, have chosen to take the (longer but well-gritted)ÌýM5-M4-M32 motorway route to Clifton this time... the idea of tackling Bristol's snowboundÌýurban streetsÌýacross the likes ofÌýHorfield and Redland didn't seem altogether clever. Or safe.

There's a well-known early '90's Hollywood film, ,Ìýabout a beleaguered local TV weatherman - Phil -Ìýplayed byÌýBill Murray. And over the past week or more, I've felt like I'm actually in it.

I've lost count of how many times I've been scraping snow and/or ice off my car at highly unsociable hours in the morning and disturbing the neighbourhood with the sound of a frantically-revving engine.

Am I actually getting rather sick of snow? Possibly.

But only because I'm experiencing (as well as forecasting)Ìýa few ofÌývery same difficulties shared by so many others across the nation: in my case,getting to work in a safe and timely fashion; but for many others, running a business; keeping roads, rail and runwaysÌýclear; maintaining vital emergency servicesÌýor for that matter, trying to take important exams as schools routinely remain shut.

A rare escape from the studio this morning, as veteran cameraman Richard Clutterbuck films a robin singing amongst the picturesque snow of Brandon Hill (while producer Robert Wicks andÌýI try not to scare it away).

I had far more fun, thankfully, later this morning -Ìýfilming snowy scenes on Bristol's Brandon Hill.

I rarely get out of the studio, so the opportunity to present a documentary feature being filmed forÌý91Èȱ¬ ONE, about extremes of seasonal weather here in the West, came asÌýa welcome break.

It'll be screened sometime in September as part of a week-long strand of 91Èȱ¬ programmingÌýdedicated toÌýBritish weather. We decided to take the opportunity of snowfall while it lasted, and get some early pieces to camera and other sequences 'in the can'.

A good call, I think: because for the next 24hrs, our concern turns to differentÌýhazards including fog, ice and ; with some very wet, windy and notably milder weather then setting-in for Saturday.

With increased snow melt and the potential for heavy rain, for sure we'll see a lot of standing water through Saturday and a risk of localised flooding.

Beyond that - after the somewhat milder weekend interlude -Ìýnext week's forecastÌýkeeps hinting at colder weather potentially establishing itself again.

I'm far from convinced that my personal version of Groundhog Day (i.e., the snowy variety) is over for this winter....ice scrapers at the ready and watch this space!

UPDATE: 21:29hrs TUESDAY 12 JANUARY 2010:

So, things now progress largelyÌýas expected from the modellingÌý(see new radar image from Met Office, below, snapped at 21:15hrs and compare to the last one from 19:45.... note how the progression north into parts of Wiltshire and NE Gloucestershire has been very much held-back and how the orographic effect remains very evident elsewhere): the northeast spread of the heavier snowfall is largely - if not entirely -Ìýnow restrained, albeit not finally resolved; the intensity for snowfallÌýtending to wane for the rest of tonightÌýbut still some heavier pulses to come on a more local scale. The trend will now see snow turning increasingly back to sleet and rain from the extreme SWÌýas the precipitation rates fall.... that process is already underway.

Fingers-crossed we'll escape serious disruption by tomorrow morning on present reckoning, albeit some areas have seen a fair dumping of snow and not least some of the upland areas duly warned of this likelihoodÌýin earlier updates.

Ìý

UPDATE 20:10hrs TUESDAY 12 JANUARY 2010:

Latest Met Office radar imagery (below, at 19:45hrs)Ìýfor the West/SW shows very clearly how theÌýnortheast extent of heavier snowfall into Wiltshire, Gloucestershire and beyondÌýwill remain rather uncertain but equally, how the orographic influence (see below update!) is having a profound effect on snowfall intensity and distribution in the south-easterly flow.

UPDATE 19:00hrs TUESDAY 12 JANUARY 2010:

The Met Office prediction has proven very accurate, with quite heavy snow falling as I write in South Gloucestershire and already around a fresh cm or so of new snow.Ìý Full marks to the folk at Exeter: this was a tricky one to call and they elected to issue their early warning way back on Sunday evening.

I'm especially impressed withÌýtoday's accurate timing of snow arrival northwards: the past three variants of the Met Office's high resolution modelling (called NAE: North Atlantic Evolution; we use this to 'drive' the raw graphics you see on TV) has proven extremely accurate. Indeed in many respects with one or two exceptions, it has proven extremely reliable for us throughout the winter so-far.

So, now the story becomes one of potentially disruptive effects.

We could see various amounts of snow continuing to fall throughout the night (waning later)Ìýand I suspect for some of you - not least atop the Mendips; Quantocks, Blackdown and Brendon Hills; some southerly parts of Exmoor especially; uplands of Gloucestershire and Wiltshire -Ìýthis could all prove a real pain by early hours of Wednesday morning.

Clearly, lower ground is also set for some degree of problems tomorrow morning too, albeit of varying severity... as I might be able to attest first-hand when trying to drive into work at 03.30hrs, so I will keep you all updated!

Ìý

UPDATE 16:05hrs TUESDAY 12 JANUARY 2010:

So, here we go.... time to watch just how closely the forecast matches reality.

It's somewhat of a moment of trepidation for those of us, myself included, who elected to 'go easy' on the forecast 'ramping' element this morning and instead took the wait-and-see approach... That's the nature of striking a balance when forecasting a few hours ahead of weather such as this and it can, obviously, go very right or very wrong!

We have recent reliable reports of light snow falling inshore at Burnham-on-Sea as the front continues to move northeast into Somerset and up the M5 corridor, with the expected degree ofÌý'orographic modulation' - i.e., the effect of high ground on precipitation intensityÌý- proving quite apparent on the rainfall radar.

One thing worth emphasising is that even at this stage, I still expect many reports from the ground to suggest a wintry mix of rain, sleet and snow is falling.

As we get into the hours of darkness, an emphasis leaning more towards snow (as opposed to rain) is expected, with the temperatures falling sufficiently further to support this change in precipitation type.

Our latest Met Office model continues to slightly ebb-and-flow with expected snowfall intensity, but it's overall offering a story not dissimilar to that explained in my last update.

So, anywhere from 2 to 5cm generally of snowfall in lowland Somerset, Bristol, Wilts, Glos and environs this evening and overnightÌýbut (and I do stress this!) with considerable variation on a localÌýscale. And just how much will remain settled and apparent by tomorrow morning in urban areasÌýis anyone's guess.

The new model also hints at clearing the front northeastwards - and by then, as a greatlyÌýweakened affair - rather earlier. Effectively, it should haveÌýfizzled-out by around tomorrow morning's rush-hour.

Ìý

UPDATES: 10:20 & 12:00hrs TUESDAY 12 JANUARY 2010:

Our new high-resolution modelling from the Met Office remains keen on the notion of bringingÌýfairly widespread snowfall across the West Country through this evening and tonight.Ìý Latest suggested accumulations (see Met Office map, below,Ìýfor general guide)Ìýare proposed asÌý2-5cm for lowland Devon and Dorset away from the south coast, with spot values around 10cm on higher ground; a fresh 10-15cm snow on Dartmoor above 200m;Ìý2-5cm snow by the end of tonight (and locally higher on upland areas)Ìýacross parts of (I stress 'parts of')ÌýSomerset, Bristol, Bath, Wiltshire, Gloucestershire, inland Hampshire and also Herefordshire.

Wales could well see the highest snowfall totals and disruptive impacts: with the topography playing a key role in modulating how much snow falls, we could see 15-20cm snow on the high ground rising north of Cardiff and -Ìýaway from the immediate coast -Ìýeven 5cm or soÌýin some of the districts actually around Cardiff itself.

The rates will lessen as the night continues, much as per earlier forecast expectations.

Ìý

UPDATE: 09:00hrs TUESDAY 12 JANUARY 2010:

We continue with various forecast uncertainties this morning. And much as I expected, it's been a very difficult few hours hereÌýat the 91Èȱ¬ Bristol weatherdesk broadcasting forÌýboth regional TV and local radio forecasts, attempting to strike the right balance.

It'sÌýbeen allÌýabout emphasising the chance snowfall later today and overnightÌýfor many districts - especially our upland areas -Ìýwhilst stressing how we could seeÌýgenerally smaller (and perhaps rather transient) accumulations at lower levels.Ìý A damb squib? Sleet or rain for some and no snow? Or very heavy snow? It's all possible.

However, the broader thrust of this morning's updateÌýisÌýto downplay, somewhat, the expected amounts of snowfall whilst reserving the strong likelihood that any precipitation falling later this evening and tonight - aided thenÌýby dropping temperatures - will do so as snow, at least for a fair part of the night.

Some of our forecast models are still eager to suggest up to 6cm of snow could fallÌýinto areas around Bristol by the end of tonight. Conversely, some other forecast models (including the French one, called Arpege) greatly downplay the totals... indicating perhaps 2cm for much of our lowland districts, at best. In fact, if some models are to be trusted, most precipitation could rapidly become a wintry mix of some snow, sleet and rain at lower levels. It's a real mess.

So, with such a complex set-up and the strong likelihood of pronounced local variation in the outcome, it's been a case of striking a middle ground. Thankfully, I've been able to offer much more explanatory detail to listeners through this morning on 91Èȱ¬ local radio forecasts.

Of course, I'm also mindful that after all manner of recent disruption,Ìýmost peopleÌýwill happily live without any extra snow causing additional problemsÌýin the middle of a busy working week!

For that reason I'm rather hoping we see nothing disruptive... albeit the potential for this certainly exists and it remains a case of watching developments hour by hour...

Ìý

UPDATES have been added atÌý19:10, 20:45, 21:45HRS, MONDAY 11 JAN 2010:

21:45hrs: New high-resolution Met Office modelling tends to downplay snow totals - perhaps around 15-20cm highest ground of the SW but more likely 2 to aroundÌý5cm at lower levels (and for many, evenÌýless thanÌýthat, I fancy).

Increasing likelihood that this will become a far more complex rain-and-perhaps-some-snow scenario, with major emphasis - at leastÌýfor many districts, especially anywhere northwards of Somerset's higher ground -ÌýonÌý the word 'perhaps'.Ìý

However, there's a broader chance of some light to moderate snowfall later into Tuesday night across many parts of Somerset, Gloucestershire, Bristol and Wiltshire.

My own punt? I'm not going to be at all surprised if we see nothing exceptional other than over the uplands of the SW Peninsula and southern Wales. But then it might have all changed by the time I'm back at work, 4am tomorrow..... keep reading; goodnight meantime!

Ìý

(EARLIER UPDATES FOLLOW)

As is so often the way in my profession, nothing is for certain.Ìý

Faced with a complex forecast still someÌý24hrs away, we'reÌýkeeping abreast ofÌývarious changes and tweaks to regional emphasis from the latest Met OfficeÌýmodelling.

Some are subtle, but - magnifiedÌýfor regional and local forecasting -Ìýthey canÌýmean major differences in getting things right or wrong!

The latest prognosis keepsÌýthe risk of heavier snow through much of the inland SW Peninsula across higher ground, but tends to lessen the snow accumulations quite markedly to the north and east of Devon and Somerset (refer to my earlier caveats in this respect!).

In many regards, it'sÌýan expected modification. I've copied (below) an updated 'best estimate' map of likely snow accumulations fromÌýthe Met Office (but don't take this as the final, definitive version of forecast reality...!).Ìý

We expect many southern coastal districtsÌýcould see temporaryÌýor indeed no snow whatsoever, but this shouldn;t be taken for granted - the wind direction will prove very critical.

So - The red lines suggest zones seeingÌý20 to perhaps 30cm of snow (and deeper drifts, it must be stressed) above around 200m above sea level.

The orange area,Ìýwidely 5 to perhaps 10cm and again, deeper drifts possible; the yellow, perhaps another 2 to 5cm widely (but more could fallÌýlocally) and outside that, yes, still a risk of 2cm+ of fresh snow... but with much lower confidence.Ìý You might see nothing at all.

I've also added belowÌý(update at 20.40hrs) another somewhat finer-resolution Met Office chart (below) with the forecast snowfall shown as black-line contours marked by their equivalent values in centimetres. Again,Ìýthis tends to highlight a broad south-to-north swathe of the worst weather affecting districtsÌýfrom Dartmoor up into central-southern Wales, with perhaps a 'snow shadow' effect reducing localised accumulations quite markedlyÌýinto parts of north Devon and elsewhere, caused by high ground.

Ìý

Compared to earlier expectations, the latest Met Office modelling also delays the arrival (and probableÌýintensity)Ìýof snowfall into much of lowland Somerset and indeed across districts further northeastwards. So for many of you, expect thisÌýto start developing asÌýmore ofÌýa Tuesday evening / overnight into Wednesday story, rather than Tuesday afternoon / late afternoon version.

I'd estimate perhaps 2cm of snow is still possibleÌýinto many lowland parts of Somerset and North Somerset; plus maybe - maybe, I stressÌý-ÌýBristol & Bath and South Gloucestershire (albeit I'm yet to be convinced), plus elsewhere across Gloucestershire and parts of Wiltshire by Wednesday morning.

Upland parts of Gloucestershire, as is often the case, could see a fair bit more. But that's subject to major uncertainty for now.Ìý

WeÌýexpect Bodmin Moor, Dartmoor,ÌýExmoor and parts of southern Wales will get a lot of snow (drifting too) but other parts of our region remain subject to considerable doubt. Topography will play a key role in both increasing and decreasing (or even preventing almost entirely)Ìýthe snowfall witnessedÌýover fairly small areas. And that's even before we add other variables, not least the behaviour of the jetstream up aloftÌýand some other key dynamic factors.

So, I'm awaiting the start of my shift again tomorrow at 4am with a mixture of expectation and yes, no small degree of trepidation. We hate getting things wrong, but hey, such is our chosen field of science and public communication... and we're getting rather used to this level of routine professional stress through this winter of 2009/2010!

Ìý

(ORIGINAL ENTRY FOLLOWS)

And it could prove somewhat of a heavyweight bout...

Just as the snow from last week continues a slow thawing process, we turn our focus to the southwest and the , stretching from inland parts of Cornwall northwards and eastwards to Wiltshire, Wales and quite possible further afield.

This time, it's the eastern North Atlantic Ocean providing the 'oomph', with a quite potent area of low pressure moving towards southwest Ireland tomorrow, swinging a band of heavy rain eastwards towards Land's End during Tuesday morning.

After making landfall, the Met Office expects - with 80% confidence - the rain to start turning readily into sleet and then snow, affecting much (and possibly the majority) of the West Country with the exception of coastal fringes.

Our current modelling via the Met Office suggests a band of snow - perhaps rather patchy at first - crossing into Somerset by mid to late afternoon on Tuesday. The winds will grow steadily stronger;Ìýindeed theseÌýbecome a real feature of the weather tomorrowÌýand will doubtless cause snow to readily drift.

By evening rush-hour,Ìýsnow isÌýexpected to be affecting the likes of Bristol and Bath, before spreading further northwards and eastwards into Gloucestershire and much of Wiltshire.

Into Wednesday morning, snow could still be falling from Bristol along much of the M4 corridor and elsewhere, but readily waning in intensity as the day wears-on.

But as the Met Office predictiveÌýgraphic (above) suggests, between Tuesday morning and the end of Wednesday, we could have seen a lot of snow and a lot of disruption.Ìý Those lines on the chart are 'raw' precipitation (i.e., rain)Ìýin mm; multiply by 10 and you'll see anywhere from 5 to perhaps 20+cm of snow could fall quite widely, albeit the northeasterly extent for snowfall is presentlyÌývery unclear.

Somewhere around 2 to 5cm would seem a reasonable widespread estimate, but with a strong likelihood of far greater totals over the likes of Dartmoor, Exmoor, the Quantocks, Mendips, Cotswolds and Forest of Dean. We shall see, but certainly this has all the makings of an event every bit as newsworthy and troublesomeÌýas the snow of last week.

Whether the snow will tend to turn quickly back to rain or sleet is somewhat hard to say presently, but it's a likely outcome for much of coastal and near-coastal South Wales; ditto more lowland areas of Cornwall, Devon and Dorset. But we shall see...

Worth adding that the strong wind will play a very important part in this. It'll be falling;Ìýthis tends to readily stick to all manner of structures and especially when assisted byÌýthe wind. We could see hefty accretions of , for example, all likely adding to the broader range of disruptive problems.

More updates, as ever, will follow on how things are evolving....

I take it the snow aficionados amongst you weren't left disappointed after yesterday's events? Of course, whilst the winter wonderland scenes offer an excitingÌý(and rather rare) pleasure for many, they also - not least many elderly and vulnerable folk, plus those trying to run businesses or simply get to and from work.

Snow 'fun' or 'hell' is of course a subjective thing, butÌýmost peopleÌýprobably wouldn't disputeÌýthat itÌýpaints scenesÌýof sheer beauty across our landscape.

It's alsoÌýa rather appealing vistaÌýfrom high above, too.

Take a peek...

This image (courtesy and UK Met Office)Ìý- taken at 1pm today - graphically shows most of the British Isles almost gleaming white from recent snowfall, with a few darker exceptions visible towards southern realms of Dorset and Devon, as well as southwest Ireland, where any lying snow hasÌýproven somewhat scarce lately.

The urban area of Bristol and surrounding districts shows clearly in this photo as a darker tint (as indeed do some cities in the Midlands and northwest) beneath gin-clear skies with very little cloud.

The snowbound mountains of Wales and Cumbria - alongside heavy falls coating the Pennines - are marked-out as if seen in an atlas. Amazing.

Centered across East Anglia, a spiral-like vortex of thicker cloud is very evident. It'sÌýa snow-bearing feature spinningÌýgraduallyÌýsouthwards, delivering snow showers across Essex and Suffolk, with further lines of showers feeding off the North Sea into parts of Norfolk, Lincolnshire andÌýNE coastal districts. Later today, the same vortex will cross south over the Thames Estuary, bringing a spell of mostly light snow into London, Kent and some other SE counties.

Draped north-south in the Irish Sea just off Pembrokeshire and down into the extreme SW of England, a line of shower activity is marked by a band of towering Cumulus clouds. Some quite heavy showers at the southern extreme of thisÌýare affecting the Scilly Isles and hovering just off the tip of Lands End. They're not expected to move much further eastwards.

Way out west, over the eastern North Atlantic Ocean to the south and west of Ireland, a conspicuous honeycomb-like pattern of cloud is very evident. It's a classic example of . In the most basic sense, air is rising around the periphery of each 'cell' to create and Ìýclouds whilst at the same time, sinking airÌýin the centre is creating a 'dark hole' representing clear skies.

It's only since the advent of that we've been able to fully appreciate such intricate, broadscale organisation of clouds - not least because individual cells can be anywhere from 10 to 120 miles across, making their true structure hard even to spot from an aircraft.

UPDATE: 04:40hrs, Wednesday 6 January 2010:
After havingÌýspent the night in a local hotel - asÌýhas my colleague Richard Angwin - I've walked through deserted streets of Clifton, Bristol, to the 91Èȱ¬ at 03.30hrs this morning. Whilst the snowfallÌýhere isÌýpicturesque, it's very evident that many roads across the region - and beyond - must be badly affected.

This morning's snowfall outside the newsroom at 91Èȱ¬ Bristol (photo: Denis Lomax)

Traffic cameras scenes I've checkedÌýon the M4 near Swindon and eastwards into BerkshireÌýlook especially grim, with just a few hardy HGV drivers risking the conditions. It's a similar story in parts of Gloucestershire and Somerset on the M5. The weather radar suggests the top of the Mendips must be especially badly hit - if you live there and can offer any 'ground truth' to this assumption, please do write here on the blog!

We're expecting the snow to continue falling this morning and only slowly wane during the day.Ìý A further 5 to 10cm of accumulation is likely across many parts of the Westcountry, but there will be a good deal of local variance as it's a complex weather set-up (and equally complex to forecast with precision, not least at a local scale!)

Wiltshire remains subject to Met Office Emergency Weather Warning for the risk of very heavy snow, whilstÌýthe rest of the region has aÌýmore generic severe weather (snow and ice)Ìýwarning in force.

In many respects, by this time by Thursday morning things could be a good deal worse: under clearing skies tonight, temperatures will plummet to around -8C (even -7C in the centre of Bristol!). So, irrespective of whatever amount of snow falls, it will readily freeze tonight and we will experience some extremely treacherous icy surface as a result.

Ìý

UPDATE: 16:50hrs, Tuesday 5 January 2010:
A new run of the Met Office forecast model now wants to take the highest risk of very heavy snowfall (i.e., where totals might exceed 20+cm) slightly further to the northeast, where the worst impact will be felt across Berkshire, Surrey and Buckinghamshire. It's quite possible we'll see major problems for the likes of Reading, Maidenhead, Slough and Heathrow before the end of the night... albeit various uncertainties remain on the finer-scale geography of this event.Ìý I'm sure the M4 (and M3 for that matter)Ìýwill see some disruptive snow on various stretches tonight.

For the Westcountry, well, we've already seen a fairly prolonged spell of snowfall - heavy at times - for much of Gloucestershire, not least over the Cotswolds. As I write, it's only gradually easing for some of those districts.Ìý I've had various reliable reports of problems on local roads in the Cotswolds, with some accidents and cars off into ditches. We have concerns they'll get a second - and probably heavier - dumping of snow developingÌýafter midnight, along with a swathe of the M4 corridor into the likes of North Wiltshire, South Gloucestershire, Bath, Bristol and later more widely southwardsÌýinto much of Somerset.

The final snowfall totals, however,Ìýlook less than earlier forecasts feared: probably a wide spread around 5 to 10cm; perhapsÌý10-15cm across parts of Gloucestershire, Wiltshire and some other spots.

But nonethless, still every possibility of seeing some real problems evolving across our transport networks by tomorrow morning...

Ìý

(ORIGINAL ENTRY)

I'm adding this entry as a brief interim blog, to offer sufficient warning of some severe weather developing over the next 24hrs.

We'll progressively see some snow falling across many districts during the course of daylight hours today but our keen attention is focused towards this evening and overnight into Wednesday, when things are likely to get a good deal worse.

We expect an area of heavy and disruptive snow to form into southern-central England, including much or all of Wiltshire later this evening, before it spreads northwards and westwards to affect the M4 corridor, Gloucestershire, Bristol, Bath and a good deal of (at least eastern) Somerset.

Below, courtesy of the Met Office's Chief Forecaster, is a map offering likely snowfall totals between now and the end of Wednesday. It goes without saying that the ramifications for transport networks could be very newsworthy by tomorrow morning.

You can see the Met Office early warning .

How bad could this be? Well, tricky one to call because variation within counties will be quite marked, I suspect.ÌýAcross our districts some areas will be every bit as badly hit as we experienced in February 2009; for others - more likely parts of WiltshireÌý-Ìýthe winter snows of 1981-1982 might provide a better benchmark, especially if we do see the sort of snowfall totals suggested by the Met Office in their chart below.

More to follow as we watch the forecasts develop....