Jackfrost

Oh wow, there's an awful lot of very heavy precipitation in this system which hasn't yet reached us and it's already a whiteout here with snow settling on top of slush on main roads, despite the ground being initially soaking wet, meaning that it's going to be treacherous come morning. When that heavy stuff does arrive it should aid evaporative cooling both here and for those who currently have rain, hopefully swinging this event further away from marginality (we had a short period not long ago when the snow turned to icy rain.) Looks like the GFS with its northern snowline has been proven wrong, and ECM and ARPEGE proven right!

Commiserations to those seeing rain: fear not, it'll turn to snow for most of you as tomorrow comes. The heavy precipitation is about to move in.

Coming down pretty hard and starting to settle here now. Absolutely lovely to see and in addition, the BBC hour-by-hour forecast now has us down for heavy snow throughout the night!

Yeah @andymusic, I'm going to go out into the garden shortly to feel that cold and the flakes. I think this might be the most marginal event around these parts that I can remember. I know not to take the BBC location forecasts seriously as they're chopping and changing by the hour due to the marginality, but I'm now down for heavy snow over the next few hours which I genuinely wasn't expecting.

Yeah, snowing lightly but steadily here too and settling in the usual places (cars, bins etc). What's your honest thought over the coming hours? I'm assuming it'll turn to rain for a while as the heavier stuff reaches us.

Very light snow falling here as the front slowly creeps in. I'm expecting it turn to rain shortly, at least for a little while.

This is still on a knife edge, as shown in that chart. Normally in an event like this, an all-snow event (I'm thinking March 2004, February 2007, January 2013), you can expect temperatures of 1°C or so in Cardiff and 0--2°C as you go a little further north, but thanks to some mild air possibly getting uncomfortably close to South Wales we're seeing variations of 6-7°C between the Valleys and coast, hence 23 cm in Brynmawr and next to nothing in Barry.

Good to see! But Twiglets, tea in a jammy dodger mug and absolutely spiffy fridge magnets? Do you want to be my new best friend, Sam?

It is looking promising with a majority of model output favouring southern (ie, the most populated and where most members are from) parts of Wales seeing heavy snow right the way through this upcoming event, but we need to remember that not all models and forecasters are on board and be prepared for the possibility that it might be a rain to snow event for some of us. I'd give the possibility of an all-snow event with accumulations as: South of a line from Cwmbran/Caerphilly/Pontypridd/Maesteg: 15% North of this: 50% Heads of the Valleys/high ground further south: 70% As for here in Nelson, the snow that melted in patches in the sun earlier today has stopped melting and it feels absolutely raw outside, a heavy damp cold.

6Z AROME which puts both myself and @andymusic in the bullseye. AROME, ARPEGE, ECM and UKMO are now more or less on board for a southern adjustment to the snow; the GFS isn't. Let's see what the 12Z brings.

Likelihood of heavy snow in South Wales increasing but not guaranteed.

Sadly Andy, my hunch is that we'll just about miss out this time; perhaps some initial sleet or snow and some light back edge falls.

This is from Ian Fergusson's Twitter: W COUNTRY (ESP. #GLOUCESTERSHIRE): Sunday's forecast liable to further tweaks, with latest @metoffice assessment bringing S'rn margin of main snow risk down a bit to lie approx Brecon-Gloucester-Banbury-Luton (N'rn edge of warning may also be modified S'wd). Updates will follow. It does seem to be creeping slowly south, and for those in South Wales with altitude it's important to remember that Brecon is actually at a lower altitude than the upper Valleys. And this is from Derek's: SUNDAY: Low pressure will bring a spell of heavy rain. Plus heavy #snow to most of #Wales. Milder in the S & SW with strong to gale force winds in the morning. 60 to 70mph gusts on exposed coasts. @metoffice warnings in force. Amber warning of snow! I expect the amber warning area will be extended slightly southwards this morning, but still very likely to not include South Wales.

The 00Z ECM has thrown out this rather unbelievable scenario, placing the upper Valleys within the zone of heaviest snow. That's 6" north of about Pontypridd come Monday morning, and it increases the further up you go.

The 00Z is coming out and it doesn't look initially great for South or even Mid Wales, but the snow spreads back south by midday Sunday with some moderate accumulations. Regarding the period where it looks like it might be rain rather than snow here: that might be the case but it's not as if we'll be in mild air, so perhaps evaporative cooling may come into play: the precipitation will certainly be heavy enough! That bastion of reliability, the BBC online, hour-by-hour location forecast, has me down for hours of sleet, so it appears to be finely balanced. Compulsive viewing... I'm remaining realistic, but with the underpinning of an optimist.

Just woke up to go for a drink and I was amazed to see that not only is it still snowing with 5 cm or so in places where it hasn't had a problem settling, but that there's more to come looking at the radar.

Light snow with flakes on the breeze interspersed with heavier outbreaks when the showers arrive over the last several hours here. Covering on most surfaces. Thanks Sam, I look forward to that update. If it's anything like the 18Z then Monday in particular will be a snowy old day as the cold air digs back in after the arrival of shortlived mild sector.

Cheers Sam. That precipitation type forecast is based on the 12Z, yes? Well, I'm being cautious but based on that and the 18Z output that Andy shared, I think it's safe to say that all hope is not lost but yes, a slight shift southwards is desirable if we're all to get in on the snow and not just higher ground.

How far south, Sam? Unless I'm mistaken, the radar forecast is premium content only (which I don't have), but the temperature profiles look broadly favourable on NW's 12Z away from the south coast of Wales, with some big contrasts: 7°C in Barry and 1°C in Merthyr, for example.

Time to call it a night, I think. The feature across Mid Wales is heading in the direction of Gloucestershire while what's following behind has the West Midlands in its sights. Meanwhile, the showers currently to the south of the main feature are largely fizzling out before they reach the southeast and besides, what is falling from the sky here in Nelson is now falling as rain. The 12Z GFS is also very insistent on taking Sunday's slider across North Wales and Northwest England. Another needlessly overhyped non-event here. 10-15 cm? Pah!

The wind needs to veer to the northwest rather than the west-northwest we currently have, or that feature currently across Montgomeryshire is going to exit Wales through Breconshire and largely miss the southeast.

My only (slight) concern is that the high ground of South Wales is currently sapping the showers of their energy, causing them to more or less fizzle out. If this continues, which I don't expect it will all night, then that snow-free zone in Southeast Wales that has been predicted on every run over the last week will actually materialise.

Ahh, I have nothing but fond memories of the run up to Christmas 2010 with over a foot of snow on the ground. Same with 2009 as it happens, with a good 10 cm lying after the Bristol Channel streamer in the early hours of the 21st. But wait, no decent snow since 2010 you say? What about January 2013 and that infamous red warning issued for Southeast Wales? It didn't turn out as phenomenally as we expected but we still got upwards of 20 cm, at least up here.

I haven't, but I'll catch it in ten minutes on the BBC News channel. Winters 14-15, 15-16 and 16-17 all featured very tame, shortlived northerlies around here which left a few centimetres of snow which only lay for a day or so (I'm guessing you got little-to-nothing down in Cardiff?) but, as we know, a more potent northerly can lead to memorable events: Dec. 17th 2010 being the most obvious, but also Mar. 1st 2006, Nov. 25th 2005 and Feb. 28th 2004. This has shades of, if not 2010, then definitely the following three. The first flakes now falling here.

Here it comes! Showers now moving into South Wales.