Jackfrost

There seems to be little doubt now that the front is decaying in situ and besides, the amber warning expires at 9. It's not out of the question that it'll all come together but it's beginning to look less likely. I apologise to anyone whose hopes I kept high throughout the day. Everything did seem to be going to plan until it just... wasn't. There are also going to be a lot of irritated people tomorrow as many schools have pre-emptively closed.

Alright, I'm prepared to admit there does seem to be a possibility, but not a guarantee, that some of us will end up disappointed tomorrow. There is more snow on the way but it might not be as heavy as expected, leading to generally light coverings rather than thick blankets. Time will tell, as always.

Well, I'm looking at presumably the same radars as you (Met Office and Netweather), and I'm watching the system move slowly north with the western end moving northwards at a slower pace than the eastern side, which signifies the beginning of the pivot. Regarding the decay in intensity, this is inevitable to an extent when a moisture-laden front in our climate runs into stationary cold air as cold air saps moisture. Those yellow accents currently over Southern England will make it to South Wales, and they're likely to be somewhat reinvigorated by the high ground here. The precipitation to the south of Wales is indeed weakening but, due to the pivot, it will soon begin to feed in from a southeasterly direction. So try not to panic.

11? Yes, that was far too early. I also feel that schools in the Valleys overreacted slightly by closing soon after lunchtime. Like I said, it has arrived a bit later than expected, and actual falling snow was delayed by evaporation for an hour or so, but it was always meant to be an evening event.

I don't mean to single out anybody in particular but this negativity is both baffling and tiresome. It is still moving north and it is beginning to pivot: look at what the eastern arm of the front over France is doing. Yes, I admit it's arrived a little later than most of us had expected but fundamentally, nothing has changed at all. Moderate snow here and settling on all surfaces.

Snowing here. It's moving northeastwards and then, at some point, it'll stall, begin to pivot and then feed in from the east.

For anyone concerned it's now too warm for snow in Wales, here's Cornwall at this very minute with police issuing "do not travel" advisories: It's even snowing in Padstow, on the Cornish coast.

Yes, it's nothing to worry about. Cold air and moisture don't mix well: not only does it evaporate but it also causes frontal systems to weaken and eventually decay, as we'll see tomorrow. It's also why, thanks to climate change, a warmer future is likely to be a wetter one, especially in winter, but that's for another time!

My timing has been a little off... There is actually precipitation over most of Southeast Wales at the moment but it's failing to reach the ground due to evaporation, something which is common in cold air but I did expect at least some if it to reach terra firma! The moderate/heavy stuff is now fringing onto the coast around Porthcawl, though, so expect it be snowing within the next hour. My forecast through today and tomorrow:

The front is slowly beginning its pivot and while it has lost some of its intensity, which is almost unavoidable when any kind of precipitation come in contact with cold air, there's still plenty enough intensity to give many centimetres of snow. Expect light snow to begin in the Valleys within the next twenty minutes.

An amber warning has been issued. The maximum depth, 10 cm, seems a bit undercooked to me, but time will tell. https://www.metoffice.gov.uk/public/weather/warnings#?region=wl&date=2019-01-31&regionType=area

10-15 cm is 10-15 cm, regardless of whether the warning is amber or yellow! Still, I'm around 70% confident an amber warning will go out this morning for Southeast Wales and the southern part of Mid Wales.

It's mostly algorithms and data rather than human input which create the hourly location forecasts, which is why there's so much divergence both between the BBC and Met Office and between locations and which is why I have more faith in what expert forecasters have to say (despite that being an unpopular view amongst some here!) There are differences in the output for Mountain Ash, Treharris, Ystrad Mynach and Bargoed, for example, despite them being so close to each other that any differences are going to be negligible to non-existent.

This is the Met Office's hourly-updated forecast for Treharris in the central Valleys, my closest available forecast location. Heavy snow for most of the afternoon and evening. As always, there's some variation in hour-by-hour forecasts and the BBC's output is likely to switch back to heavy snow at some point this morning. In other words, don't take them literally or even too seriously.

The front is guaranteed to lose some of that intensity (in other words, expect those bright reds to be replaced by mostly greens and yellows) because it's running into cold air, and as cold air holds less moisture it'll sap it of some of its intensity, but not enough to avoid disruptive snow in favoured areas. The orientation of it will also change from a NW-SE-aligned system to a W-E angle as it hits the cold block and is unable to progress further, and it's in this position that it'll begin to fizzle out tomorrow.

I'm not concerned about this. There's always some natural variation between both the model output and various TV forecast graphics. Frankly, unless and until the Met Office, BBC or any of the main forecasters for our region (i.e. Derek and Fergie) dramatically change their tune, I don't think there's any reason to panic. Not to be dismissive of ITV's weather department, but as with C4 and C5, they've never been held in as high regard as the BBC or Met Office. We've been here plenty of times in the past; the Mar. 2018, Dec. 2017 and Jan. 2013 events jump immediately to mind. Frankly, we spend so long chasing a significant snow event and when they finally are on the brink of materialising, I suspect we become doubtful because we subconsciously can't believe it's actually happening.

Yes, fear not @whiskers, we'll have our snow! I'm trying to think of historical precedents for this... Does anybody remember the March 11-12th, 2004 event? Similar synoptics and depths, even similar times of day and night, although this time the snow should stick around for a few days instead of an immediate thaw setting in.

I think there's a bit of confusion involved here: Fergie tweeted two charts, one from Jan. 23rd and one from midnight, to show how the forecast can and does change. The one from the 23rd showed a rain event, the one from midnight shows the snow event, which is still very much on.

My predictions for this evening's event.

Great stuff. Where did you see that? It sounds like he's going with what the snow acc. charts are showing rather than the revised warnings of 5-10 cm for Southeast Wales.

I’m no Steve Murr, but I’m expecting the first flakes to flitter out of the sky around midday.

Yes, and based on reports we've had from points further west and the quick transformation now taking place on the Heads of the Valleys, I expect the change to be fairly rapid.

Probably not, sadly! The depths we saw in March would have been fairly unusual in a pre-climate change winter, let alone now. Some scenes here in Nelson:

If that was a reference to my post a bit further up the page, the Swansea area was only ever really predicted to see a wintry mix due to its coastal location. Expect to see wintriness in the Valleys in the coming hour, with some settling snow in higher parts.

Just a reminder to anyone writing off today that: a) the warning didn't kick in until midday; b) the main front with the embedded colder air is currently moving into the Swansea area (hence @Marcus_surfer seeing snow), which means that points east of here and still likely to be seeing rain and sleet; and c) today was never expected to bring widespread significant snow anyway.