gottolovethisweather

Pattern change post my watch period (10th through 13th) I reckon. The models are struggling to get a grip on things as early as D4 and with all the differences noted intra-runs, may well be that Shannon has re-entered the room. I do feel, however, that, a colder than average period is upcoming for the second half of December. Your region and in particular Northwestern Scotland is likely to feel the brunt of it before hopefully extending south thereafter.

Everything is as expected over the next few days with us all seeing a weakish Westerly regime taking over. The resultant Jetstream profiling forecast by the GFS 0z on the 2nd December, some three days ago was this. It matches closely to the corresponding ECM chart for t+72 hours which is replicated below, not many differences between the two if you were to overlay the NH Jetstream profile over today's ECM. However, two key regions to watch for upcoming developments are highlighted in red. Bear in mind, my watch period was and still covers the period between the 10th and 13th December, which should see a relatively small yet still significant pattern change after three or four days of unseasonal warmth by day and night. Why am I so confident in this being a crucial timeframe, well because it has been showing hints of it across all model suites (particularly the 0z and 12z suites) for a number of days now. Additionally, take a gander at the GEFS ensembles spreads which further back up my suspicions of a pattern change of sorts. The greatest divergence on the above GFS 0z spreads begins around the 10th and 11th December in all instances, so I suggest this is precisely when our confidence in any given prediction should start to wane. We will clearly know more as to which direction we are heading in beyond the 10th/11th by this Thursday or Friday. To which pattern change, I hear you ask and that is as yet, unanswered. We have option one of an increasing ridging influence up from the south again. Option two being an outside chance of a brief (duration unknown at this range) period of Northerly-based winds, it's a 50:50 chance, either way, IMHO. Beginnings of a split vortex as early as D4 (9th December) which ties in with other outputs and those previously mentioned confusing NH Jet Stream differences. D5 (9th December) chart shows first hints of an incoming Northerly flow, but equally, increasing heights up from the south-west approaches looks just as feasible. By then, however, the unseasonal warmth will have likely departed our shores towards Europe. Any point in me second guessing what mid-December might look like, nope. For fun I'll throw in one of tonight's ECM operational suggestions. The following ECM D8 chart respresents the end of my watch period and shows a NH profile in turmoil, so I have very little confidence in that chart verifying, however it does illustrate the great uncertainty past next weekend if you ask me. All the best then, my advice is to step back, have a good few hours off our personal attempts at cross-model analysis and give things another day or two. Have a mince pie or three, a class of prosecco or beer and come back for tomorrow's model rollercoaster ride. A pattern change (NOT an entrenched cold delivery version) but a change of sorts is a-coming before the third week of December begins from what I can tell.

Oops, yep, you got me there I'm Dreaming Of. Although, a period of really high Temperatures is currently set to peak on the 7th and 8th December. After that, the behaviour of the Jet Stream alongside other determining factors are likely to negate too much unseasonal warmth. Dull skies and unwelcome cloudiness will likely be more of an issue next week to those wanting something cheery at this time of year, but beggars can't be choosers. Incidentally, the UKMO 12z operational run isn't buying your dire PV setup either as early on as D6, so some hope there too for coldies.

Yes, a mini heat burst (relatively speaking) is possible, might see maximum Temperatures of 15-16c in places that day.

Yes, the NH Jet profiles around D4 to D6 are intriguing, to say the least, as I noted yesterday. While some in here clearly appear to be given up on their cold weather searches, I would say one should NOT be looking too far ahead for signs of changes. The period between the 10th December and the 13th December is my latest watch advisory!

Hi Nick, I'm not sure if we're speaking about the same thing here but I mentioned it in passing a couple of times yesterday on here, the timescales involved seem to match up. There are hints now also off the Eastern seaboard of Atlantic heights returning by then. The latest 0z UKMO operational run seems reluctant to drop any heights down IMBY either. Thi could indeed become a very short period of Atlantic influence (largely biased towards affecting NW Britain anyhow) as things stand, given the uncertainty from 10th December onwards. It has made for some fantastic reading in here this morning, so much better than those one-liners.

Indeed our eyes need to be drawn to developments of the Eastern Seaboard post D5 onwards, as alluded to in my post from this morning.

Indeed our eyes need to be drawn to developments of the Eastern Seaboard post D5 onwards, as alluded to in my post from this morning. We certainly need to look at how the NH Jet is handled by cross-model outputs from D5 to D7 in particular when prejudging FI outputs. I don't think the mid-term is nailed yet alone Mid-December and beyond, although we are receiving some sound guidance from a few respectable netweather members, who clearly know the time of day. And as if by magic, the HP influence is shown to be stronger than previously modelled by D6 (8th December) according to UKMO 12z. A case of what's changing IMBY, very little, that's what, lol. Will the ECM 12z follow where the UKMO left off? Perhaps it's time to adjust my percentages in this morning's post to something more akin to a 50:50 chance of an Atlantic influence taking over from a 70-80:20-30 percentage chance by this time next week.

Hi, all. One thing to keep an eye out for is just how the NH Jet is forecasted to act over the coming days. At present, the start off point is a very blocked Atlantic setup as shown by this GFS 0z t+0 chart. Come D5; we are beginning to witness changes, but they aren't really notable until then, next Wednesday, our weather isn't set to be affected by changes in the Jet beforehand. Before this, it is a case of as you were, dry, on the whole, some frosts and sunnier days, others cloudier, temperatures on the cold side for most. The highlighted regions in red are ones to keep an open mind about because changes in the Jet profile off the eastern seaboard of the US up to D5 will have large ramifications for our weather into the second half of next week and beyond into the middle part of December. The black arrow doodle shows the probability that the Jet might dig yet further South than the GFS (as with all current modelling) predicts. The final chart I'll put up is from the first day of the newly emerged milder spell (IMHO a 70-80% likelihood of occurring) so still slight potential for things to alter at the surface yet, given the timescales involved. However, what is equally important for coldies is the forecast NH Jet at t+162 doesn't come about as suggested. Again my hashed out area encased in red and the black arrows hint at differing probabilities to those currently expected. Beyond this, I'm not endeavouring to suggest what might happen, synoptically, although I do currently believe down in my region (central southern England) not much will have changed, yes it might be milder by day with fewer frosts around, but there won't be much rain around again if any. The period up to Mid-December (8th through to 15th), therefore, is STILL very much up for grabs in my opinion.

Yes, seems I might need to eat a slice of humble pie after responding to SS and his GFS op post, based on this one run, again showing things getting a tad milder. Then again will it be colder at the surface given high pressure hangs on overall? Inversions anyone? As a coldie, I'm not panicking unless this becomes a trending trend and what's a few milder days in the scheme of things, aye. Besides the Atlantic train is still derailed even then (December 6th) for all, away from the far NW and nothing is nailed past then.

Yep, I wondered the same but to be fair to Summer Sun he has now added the following "Whether it does turn milder for a time remains to be seen". Moving on......

Yep. same goes for your post up thread suggesting we'll be bathed in above average Temperatures by next Thursday, I'll believe it when I see it, although not implausible. I expect the ECM 12z to remain on course, showing very little in terms of mildness about the UK in general come D8 to D10.

Thanks for your help, guys. I see tonight is predicted to be a night of generally less severe frosts. According to the Beeb forecasts I've seen, this GFS t+21hrs (7am December 1st) chart from the 6z showing relevant 2m Temperatures should be somewhat accurate. This is obviously what I should have been looking for, before getting confused with my 850s and inversion issues. You live and learn. I will also keep an eye out for dew point charts in conjunction with the forecasted 850 charts, thanks Nick F. Simply proves to me, we shouldn't take everything at face value and need to account for several parameters at once when second guessing what the model predictions are indicating at any one time.

Ok jvenge, Thanks. Anyone got an example they can show me and all others remaining confused by this important topic?

And those old hands as well, don't forget, Pete. Quite a rare event I imagine Frosty, yes. My question from yesterday remains unanswered. What other pointers should we looking for in the models other than the 850s should we be considering when looking for cold?

I think you might falling into my trap? It will already be nicely cold at the surface I think.

Thanks @MattHugo has also mentioned these among others, I knew such things existed but couldn't connect the dots.

Yes, Nick, they seemed way too high for today. Thanks, I thought inversions were something to do with it but couldn't see how they related to actual Temperatures on the ground. How come then when most of us chase charts in deep FI with -5c or below 850s are we not happy when +4c 850s can bring entrenched cold? This bit just seems odd to my mind, especially when the warmer oranges and yellows come in and everybody (not ALL) overreact to said chart when in reality it could be darn CHILLY. Simply proves to me that 850s are NOT the only indicator for cold, in fact (here's where your knowledge comes in) what else should we be looking for, Nick L or anyone else?

When speaking of 850s does anyone know what today's forecasted figures were for my area (Newbury, Berkshire) as I wasn't far off an ICE day in the end. I reckon tomorrow might yet see one in my region somewhere locally? That's no poor show for late November in any recent year for sure. Here's the ECM 12z take on the present 850s which is what confuses me somewhat. Anyway, onwards and upwards from here. Will it be HP all the way in one form or another, I think it will?

And all at t+10,800 minutes distance at least before the forecast breakdown (albeit temporary in nature) even if it does occur. The high sinks one way then the tother, increase in strength and decreases. It matters not, the planes (NWP outputs) are stuck on the runway and aren't flying anywhere soon, we are stuck in the HOLDING pattern for many days yet. Note to all. Not quite sure why certain members get ridiculed when speaking of the reliable but there you go. Personally, I make FI as somewhere around December 6th at the moment while shortwaves or surface feature developments, far from our shores prior to this, will likely alter current projections slightly. For now, its HP dominance and I don't see that theme relenting for several days yet. Tonight's ECM will probably be similar to yesterday's in its evolution if you ask me, but time will tell.

Think frosts, ice days, light snow flurries at other times, and it's undoubtedly a resounding yes. The air flow (sometimes a SEr'ly, at other times a NWr'ly or anywhere in between) will fluctuate significantly, though, as will cloud cover day by day, so never a gimme generally speaking.

Indeed Nick. And past history tells me that the longer we are in this HOLDING PATTERN the better, the last thing coldies want is a moist strong SWr'ly flow at t-72 hrs. The Atlantic seems to have gone into hibernation for sure, long live the holding pattern and a chance to chill the ground for many more of us.

And of note yesterday's ECM 12z had cold uppers incoming from D5 or thereabouts too. Feet firmly on the ground but tentative signs of the dice being loaded towards colder scenarios if still dry for the vast majority. I believe the short-term pattern will likely upgrade too, with Countryfile and tomorrow's Beeb forecasts hopefully showing the first hints at this. Cannot rule out the odd warmer day but as stated earlier much of the near-term forecasts hint at double-digit maximums being a rarity away from the far NW throughout the whole of next week and potentially beyond. BANK!

You might have to go your GP if that truly looks like Stewart's face I reckon, lol. Or if like me, Specsavers. GFS latest a bit of a snoozefest but no broad changes in the next seven or so days so no panicking from me. Could turn mild, could stay on the cool to cold side by December 2nd or 3rd, will be largely dry up to then, a case of as you were, outside of deep FI.

Indeed Phil and precisely how the Jet split is handled in subsequent runs will be most telling. In your experience, is this what is causing the mixed messages from the modelling (all NWP suites) post D6 or thereabouts? I'm presuming it bears relation to where the Atlantic trough positions itself.