Stu_London

A nice 06z operational to look showing a prolonged cold spell pretty much nationwide from the 27th. This could be brought forward a bit if the low slides a bit more. On the flip side still nearly half of the ensembles do not make anything of the cold spell at all. Starting with today's 12Z suite we are in for 48 hours of a rollercoaster. I would expect the pattern to resolved by Monday, with any individual features to firm up later in the week. So - where's your money? I would go: - 25% decent (4 days plus) cold spell with most or all of uk included. 40% some sort of regional event with perhaps the south missing out 35% diddly squat.

Doubt much will change when we get to 72-96hr range - so we have about half amount of those runs for the picture to change significantly.

Severe wintry weather for most of the UK is never simple. If there is an escape route from it, most of the time the weather will find it.

18z op a bit of an improvement on the 12z op - but GFS still keen to blow up the atlantic in FI. FI still looks like 21st December onwards to me with a spread of 10C on 850s between the warmest and coldest. Still lots of good ensembles but I'd say today has taken a small step backwards in respect of severe wintry weather rather that the small step forwards that most would have wanted. Weekend runs will most likely get us some cross model and ensemble agreement up to the big day. Still all to play for but not much more room for downgrades before this is a bust (in the short term), in my opinion.

My take on the morning suite The scale of run to run changes around the 7-9 day period tell me that this period is still very much FI at the moment, so looking at specifics is pointless. Overall, the prospects for a cold spell with snow over the festive period has downgraded slightly this morning - negatives - some of the operational runs looking a little ropier this morning - positive - slightly better ensembles, particularly just after Christmas. The overall NH profile with lack of any vortex organisation gives us a high chance of a decent cold spell in the next few weeks, even if it is not in the next 10 days.

Some nice model eye candy tonight. Whilst ensembles are improving there are still too many that go the way of the control run or similar busts to get carried away just yet. Day 8-9 still FI - particularly with an easterly involved. Prefer to see where we are in 3 days time before I start lobbying Boris to call Cobra meetings.

Thats been there on a number of runs - has headed due north previously

06GFS is probably the most interesting operational run and suite of ensembles for the entire winter so far. Still quite a big spread after 19th/20th December but in the case of a lot of members (like the op) it is just a delay to colder conditions. The big issue for me is that there is still a lot of variation run to run and between ensemble members. Understandable at +8 days, but would like some consistency by the weekend, as variation is the way the UK normally escapes these kind of set ups.

06z ensembles undoubtedly colder than the 00z ones. Big spread also which starts around 19th December. Let's see if the trend continues with the 12z - I feel as soon as the period 19th to 23rd tightens up, we will have a better idea of the longer terms prospects.

Only need to get below 4.8C for the coldest month since 2010. I'd say that is probably marginally odds on at the moment, given the outlook. Of similar interest is whether we can get to 3.7C ish - that would bring us our first sub 10C calendar year since 2013. I think we would definitely need that cold spell in the final third for that to happen, unless the high pressure becomes very cold with freezing fog during daytime, which would be another route.

Could be a month of two halves Cool and unsettled H1 ????? H2 Depending on whether we get some blocking and where it sets up, could be fairly cold at the surface and dry, or something more with more wintry potential. Personally don't mind either, prefer it to the current set up, so hoping the pattern change happens.

The worry has to be if the vortex gets too far away is similar patterns to those we experienced in at the turn of the year - brilliant northern blocking but pretty tepid uppers - it was cold enough for a few snow events, but many found themselves the wrong side of marginal.

Looks like MLB is the new trend. Seasonal at the surface, but all the cold pools have imploded.

Models seem to be converging around the idea that the storm winds up, gets close to British Isles, then starts to fill and sink south. Very windy in the west, but I think heavy rain might be the headline maker if frontal systems become slow moving. Interesting that when modelled in FI - a lot of the output had this storm barrelling through and disrupting the block to the east - now it looks like the theme is that low pressure systems will struggle to get east of the meridian. This might allow some influence in our weather from an easterly direction further down the line, however just as likely is that the UK gets stuck in the middle of a Mexican standoff between the Atlantic and the block, with southerlies over the country.

Just on the raw data - 3.7C would deliver a sum 10C year, but as Roger states there may be some differing methodology at play, so perhaps a tenth or so lower. The first couple of weeks of December look cool to average, so some sort of cold spell in the second half would put this in the mix. Seems like a million years ago when we got sub 9C (2009) - not sure the like of which I will see again in my lifetime.

Very good video forecast - explaining the situation very well. Looks like UKMO have this a bit further north than some of the other models, although as Alex Deakin notes, a fair degree of uncertainty at this point. Does look like the first Atlantic 'bomb' of the season however and sure to have some impacts, most likely to ROI and western parts of the UK.

Thanks for this thread. I'm sure as and when cold snaps/spells are approaching it will come into its own. I try to post in here as well as still using the other thread for longer terms thoughts. looks like a fairly cool showery regime for the next couple of days. Maybe a couple of transient wintry surprises as we are close to marginality with uppers and ground temps at times. All eyes have been on the atlantic storm for next Wednesday - still lots of uncertainty at 108hr as to how strong it will be and its track. Latest feeling is that the mainland Europe may get the worst of the conditions. Likely to have a big effect on how conditions will develop after its gone, so one to keep an eye on for both short and longer term prospects.

Got to hope the GFS is over-egging this storm for next week. Would be horrendous for rush hour on Wednesday morning with the winds on the southern flank. Probably not quite October 87 - but would be a big headline maker, all the same.

Looking like the most mobile period of weather that we have seen for quite a while coming up. Looks pretty westerly so the probably only Scottish and northern hills seeing anything remotely wintry when the pattern takes hold. To be fair, even when the easterly was being shown as possible, most runs were blowing it away after a day or so - it never looked like it could sustain for very long. In fact, the models have been quite consistent on a theme but have shunted everything east a couple of hundred miles. That said, it doesn't 'feel' like the sort of winter where a zonal pattern dominates for too long, so I would be looking for the next trend to emerge from mid December onwards.

All the really interesting stuff (if there is any) is way beyond the reliable timeframe. I don't expect the models to start to converge for a while yet for the mid December period - perhaps another 4 days before we get a clear signal. Much as it looks amazing, I am not buying the ECM at this point. On the flip side the GFS is probably up to its over progressive tricks again. I would recommend that until some sort of pattern emerges with decent cross model agreement and so sort of ensemble trend, then just enjoy the rollercoaster and don't get too hung up on specifics. While the background and teleconnections aren't looking too bad, the UK has a knack of avoiding (completely or the worst of) cold spells that look like that are coming down the track.

Models seem to be backing away from us getting too much influence from any Scandi High. I think that was always on the cards as there had been plenty of indicators that Atlantic mobility would uptick in December. For me, cold snaps before Christmas are a bit of a bonus anyway and as quite a few have seen snow from this weekends storm plus another little snap from northerly later this week, we are doing ok in that respect. If we are going to get a Scandi High this year, lets wait until late Jan/Feb when there is likely to be a better cold pool and a better chance that it won't be blown away at the first attempt by the atlantic

Tunbridge Wells - light rain.

Still fairly clear and not excessively windy in Tunbridge Wells Not expecting much more than a few flakes mixed in with the rain. Some of the higher areas of the downs might do a bit better.

could do with a few more upgrades for Saturday. If that band comes down the east side on Friday night, then its easy to envisage a situation of snow falling through the air. However getting it to stick and last more than an hour or so on Saturday morning looks challenging based on current output

Well - in the absence of heights truly establishing themselves over Greenland we are left with an early season mid latitude high which will sink and let the jet over the top eventually. An early cold snap for northern UK with some wintryness particularly over high ground. A more seasonal feel for the midlands southwards. Wouldn't be looking for a scandi high at this point in time particularly as it looks like sinking into SCeuro high with the jet riding over the top. These scenarios often lead to the UK stuck in a tropical maritime flow. These highs rarely regress northwards, they just hang around or sink into a bartlett type feature. The good news, I think, is that I don't think we will get stuck with repetitive patterns for too long during the first half of winter and model watching will be as exciting with as many ups and downs as last year.