Fergies latest posting interesting for Wales
Not really sure where all this misguided 'GFS is rubbish' twaddle emerged on here (we're discussing computer models, not football teams)... but to return to the focal point of Sunday, which we anticipate could deliver a significant snow event:
At stake here are some marked differences in the rate of E'ward frontal progression into the UK between the 12z UKMO-GM and other operational centre output, notably ECMWF. These appear correlated to the rapidity and scope at which the amplifying upper ridge over the country on Saturday cuts-off. For example, the 12z ECMWF deterministic is markedly slower with this process compared to UKMO-GM, with net result of retarding the frontal progression to a greater extent. This slower solution is favoured by Exeter, who have modified the GM accordingly (away from raw version you'll see on websites).
Clearly this has profound implications in what will prove a high-stakes forecast, should current evolution continue in similar tone. Bear in mind the frontal zone in question is only just now taking shape off E coast of N America... still a way to go on this story.
However, the slower EC (and presently modified GM) solution offers less threat of disruptive snow into London during Sunday, as opposed to raw GM, which did. Hence, this sort of issue - high stakes, as I suggest - remains a clear uncertainty.
The consensus solution follows EC's snow accumulation prognosis (sorry I'm not allowed to share that as actual mapping), which - with frontal leading edge moving into sub-300m WBFL air across much of S England & Midlands/Wales - looks a decidedly bothersome blend. EC offers as much as 10-15cm snow anywhere from approx central Somerset up through Bristol, eastwards to around Reading and north through pretty much all of Wales and West Mids (some peak totals in these areas excess of 20cm). To the SE, similar amounts (to around 10cm) across Wilts, Hants, to W Sussex. Clearly, distribution is uncertain but in broad terms, the combined weight of EPS and deterministic output is indicative of parts of W/S Scotland, eastern Northern Ireland, N England, Wales, West Country north of Taunton, West Midlands and southern-central England being most at risk of disruptive snowfall durIng Sunday and overnight into early Monday. Currently, Exeter suggest 30% chance of some snow into London itself later on Sunday, albeIt any ccumulations here in the capital are thought likely to be pretty small.
Anyway, that's some detailed thoughts for now, ahead of whatever the 00z runs might yield.