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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 ´óÏó´«Ã½ 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 ´óÏó´«Ã½ 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....