Model discussion highlights

[bluearmy]

Possibly seeing a destination and evolution for two weeks time 

Every chance that in week two we see an amplification of the euro ridge north but likely on a positive tilt of the northern arm to our west. This is well advertised on the gefs in week 2.   Nwp then trends to a notable Alaskan ridge which drives a downstream trough and takes the ne canadian vortex axis away from the Labrador Sea  and into e Canada.  Gefs and geps are then flattening the sceuro ridge with a weak areas of low anoms headed towards n scandi.  These two evolutions could allow the sceuro ridge to then retrogress into the Atlantic and some  WAA driven by the upstream trough could deliver enough amplitude to bring colder air south across nw Europe 

this isn’t a prediction but it is a way of putting some of the jigsaw pieces together which fit telecon expectations for early feb (and seasonals ). 

shame we can’t see ec46 week 3 clusters. 

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5012993

[Midlands Ice Age]

Seriously though things are still interesting.

Since Tamara   and   the other experts called this week broadly correct, (with the slight exception of the cold air further south for enough time to cool it down enough for a long term cold period for most of us), I am looking into the forecasts with a view for their predicted forecast of cold to return quite soon. Still a possibility.

Currently looks a bust, baswd upon the last 2 or 3 days..

However experience teaches me that many a cold spell has developed on the back of a rapidly deepening low moving across the southern half of the UK. This now seems pretty  certain for the weekend.

With cold air still over Scotland and the north, this air will  get dragged southwards again early next week. as higher pressure will start to develop on its western side in response.

This could take us back to a much colder outlook again.

If it does it would fit the pattern exactly described by our experts that they expect to happen, as the higher pressure would push and would slow the Atlantic down again, hence  giving it a chance to  move to our north again in their classic 'eddy' descriptions of atmospheric events...

Let us see what happens.

MIA. 

 

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5012883

[Man With Beard]

The ICON accumulated precipitation chart up to Saturday is a bit of slap in the face for snow lovers in central and southern areas - precipitation virtually everywhere in the Atlantic and Europe apart from here!

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013129

[Catacol]

For those looking further out, JMA monthly published yesterday for February.

UK, as usual on this one, at 10 o clock.

Otherwise the current situation is not what many on here would have hoped for. This GFS for tomorrow screams all kinds of wintry wonders:

but closer examination shows that much of central and southern UK is stuck in a col, neither fed by the strongest and coldest winds from the N and/or NE nor quite in line for the channel runner. There is a day or so to go for surprises to turn up, and as we speak Scotland is getting pasted....but the snow hungry majority in the south are left gasping. Feels like rolling a double 1 and damnably unfortunate.

Then comes week 2. 22-29 Jan approx was always flagged as a week of greatest concern because the impacts of lowering momentum would be greatest and the need to gave got a block cemented in a good place would be highest. But that double 1 effect may be about to land again. (is that like rolling 4 x 1s?!) The strat splits tomorrow

and the zonal mean is much below average, even close to a technical (if very short lived) SSW

- and we could be excused for thinking that there is little better context for ongoing northerly blocking. But look how steep the recovery is, and with little to no model disagreement. Back to average in a flash, and GFS largely puts the vortex back together again by the end of the weekend.

So - what's happening?

Factors leaning towards a cold and blocked outlook have had to work pretty hard to get our blocking pattern in place. Even with a favourable pulse of momentum, a good GWO orbit, and lagged impacts of an amplified MFO through the west pacific we have not quite got the block in place. Meanwhile, as soon as those signals fade into a period when it was well noted that things would get less automatically "good" for winter, we get a collapse of the pattern that is on the crazy side of fast. We go from the good chart at the top of this post to this within 4 days:

No obvious lag here for the flatter MJO phases!! And a reforming vortex has helped support an atlantic pattern in double quick time. It is almost as though the wax wane nature of the atmosphere has been placed on a hill. To get to a blocked phase we have to sprint up the hill on our bike, in first gear, legs pumping and burning once at the top. But then to return to the starting point it is an easy cruise downhill, hands off the handlebars, freewheeling.

Maybe this is CC in action. Or maybe it is just a reflection of some very poor luck for the coming week and the one after. I don't know. I guess in the end, other than to take the learning from it, I don't really care. It has never been easy to get snow to this country and 1988 to 2008 was a 20 year run of misery punctuated by a couple of good moments. Hunting those rare major snowfalls would be no fun at all if they came every year.....but it would be good if the fates could allow us 1 in 5!!

This winter is not done. I read some guff on this thread that I find annoying, folk announcing the default return of a period of westerlies as though there is something wise and significant in doing so. Saying the UK will usually have westerlies and that the best way of approaching UK winter weather forecasting is to say "westerly" each time because you will usually be correct is both lazy and daft. I don't put my money on Ronnie O'Sullivan to win the snooker each time "because he usually does." I do it because I analyse the context and decide it is the most likely outcome....and I might still put £10 on a young outsider with half a chance of making it based on analysis and form, as per Luke Littler in the Darts. If Ronnie is ill the week before Sheffield I probably don't back him at all, despite the past run of success!

And this is where we are right now. January 15, half way through winter. We had a decent start, a disappointing Xmas/NY and now sit in 4 days of frigid air but without widespread snow forecast. Bugger. Westerlies to return for a while. But the analysis doesn't change, and the weighted approach to appropriate forecasting remains. The next momentum cycle is underway, signalled by rising frictional torque as of a couple of days ago. The MJO will be back in the west pacific pretty quickly looking at model forecasts, and while the vortex returns to average it doesnt appear to launch itself into an above average phase. Read Tamara's work rather than mine on this - she expresses the technical aspects of wind flow much better than anyone else on here....but in essence we are set to have more wave action return, a meridional pattern embed and poleward flux that should bring blocking back to the table quite quickly. I haven't seen a seasonal do anything other than go with a negative AO for February and the combination of high momentum and a favourable MJO in a Nino year will bring things back. I had said 3-5 days of atlantic westerlies. That was based on the cold hanging on until Sunday as I had it down as a cold week....but it appears the cold is fading faster than we might reasonably have expected....so it pushes longer. I do think by the end of week 2, that's somewhere around 26/26/28 Jan, we will have a more favourable context back on the table....or at least sitting on the hot plate waiting to be served.

Winter hunting in the UK has never been easy. C'est la vie. But we continue to look, and search, and roll those dice despite the fact that 80-90% of the time they don't give us what we seek.

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013243

[Battleground Snow]

On the end of the gfs run we are still being plagued by euro heights, but pressure is increasing to the north east, while starting to weaken to our south.

Will be keeping an eye on the ecm eps over the coming runs to see if this solution can gain any traction.

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013308

[Scott Ingham]

14 minutes ago, Battleground Snow said:

I'm just starting to see some signs of life in the extended,

Would be nice to accelerate towards that solution, ecm does get to phase 7 faster.... So extended EPS may offer some further hope tonight.

Control, attached, alongside couple of the best gefs members, also attached is the mean anamoly.

Let the next chase commence!

Look at that date mate 29th for the change! Surely not 2 in a row! Fits in perfectly with retrogression into the back end of the first week of Feb! 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013385

[bluearmy]

2 hours ago, Ali1977 said:

This will stir things up - a cracking Feb on the way hopefully - and March. As per the long range METO really ️

I’m astonished that a pro like Marco is making such a big deal of the ssw. It barely gets across 60N 10hpa and 

and by day 6 we’re here 

 

if feb sees downwelling waves  which deliver a strong neg AO and perhaps wintry conditions then it won’t be anything to do with the next couple of days in the strat but the last couple of weeks that have seen repeated negative flow above 70N down to the trop and which culminate with the next few days which squeezes a tech ssw.  Perhaps one of the weakest and shortest tech ssw’s we will have ever seen ? 
 

and one for @Mike Poole  - showing the positve flow headed up through the strat as opposed to what we’d expect which is the strat influencing the trop over time 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013582

[Mike Poole]

Plenty of uncertainty early doors on the ECM clusters this evening, then - from a point of view of looking for what might come after the Atlantic spell, here’s T192 onwards.  

Pretty much 3 shades of zonal until the extended, where once again, the signal is for a build of heights to the NW, most notably cluster 2.

I was struck by the 46 Hovmoller plot tonight actually, there are clear changes suggested:

You can see the Greenland block (upper B) collapse, to be replaced with a zonal period Z where things are clearly moving (diagonally on the diagram) east to west.  But then there is a second blocked phase (lower B) which is transitioned to around the 25th January, with blocking just to our E.  Later on than that there’s a hint of retrogression.  This is the next opportunity for a chase into February, looks a bit earlier on the 46 than suggested by the EPS.  

But for now, enjoy the cold weather this week before the wind and rain returns.  

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013648

[Cambrian]

Just for fun at this range, but interesting to see the end of the 12z GFS control run obliging our winter interests by getting the jet stream north all the way through Svalbard, a very solid build of heights and a surface high over Scandinavia, an easterly flow and a most interesting T850 chart! 

   

Support from the ensemble mean for a sustained rise in pressure and for the northward extension of heights into Scandinavia.

 

One door closes and another one opens….

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013532

[MATTWOLVES 3]

9 minutes ago, Bricriu said:

 

 

Very disappointing. A high in situ that just eats  up more of winter. Still it's better  than a zonal onslaught. 

Forecasting a block is one thing but predicting where its sets up shop in 2 or 3 weeks is a whole different ball game. The ec regimes do highlight a blocking probability,the met also bring this up,and the fact they mention North or East winds show there's a chance of a favourable positioning. Also worth looking at the JMA and recent glosea modles to also see how blocking is currently a form horse. EC will probably drop that idea tomorrow before planting it slap bang over Greenland the day after..The signs I feel are about to improve.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5013565

[MattH]

It is highly likely that the rest of January, beyond the end of this week of course, will 'come and go' with no significant cold synoptics in play. We look towards February then for the renewed risk, which still hasn't changed.

January, overall, mind is likely to be something of a disappointment, as the change to colder synoptics now most certainly wasn't expected to be removed as quickly nor as easily as is now on the way from this forthcoming weekend onwards.

The ebb and flow of the processes behind the GSDM certainly have some influence here, despite clearly the AAM not falling anywhere near the same levels as we started off the winter, back in the first half of December. As I mentioned the other day though it is the strat developments, especially within the lower levels of the strat, that will primarily aid in changing the pattern. The recent pushing and pulling of the vortex, with a low-level split (circa 100-150mb) an evolution that could not have been foreseen some weeks ago.

We can see this again on the PV plots and the standard 500mb height charts...Note the split and separate lobe over N America, ejected eastwards and boom, a return to a solid vortex in its usual locale.

It is this, without question that is the key driver for the rapid change to a more +ve NAO regime looking ahead - Ironically, it has been the troposphere that has 'led the winter dance' so far, with the stratosphere having little influence, but the recent weakening and split of the vortex, again ironically, actually helping now to end the current cold spell and bring us back to a more 'usual' winter time pattern. If the split hadn't occurred or occurred differently, then the outlook may well have been different, but that's all 'if, but and maybe'.

Looking further ahead there is still no reason to write off the rest of winter, in any shape or form - The MJO remains active, another +GLAAM is on the way and just as happened in late Dec/early Jan this will be another interesting "test" of the processes at play within the GSDM to help alter the up-coming +NAO pattern. There are likely to be a lot of hard-going synoptics to get through first and, again, by the looks that will take us now to the end of January at the earliest.

Cheers, Matt.

 

 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5014150

[Daniel*]

It’s not pretty viewing but I wonder with rising AAM tendency a currently modelled very mild Euro high turns more into a mid latitude block which allows for more chance of frost and fog especially further south. With AAM looking to rise more empathically in Feb this could then become high lat based. Some stormier weather to come but generally I’d say high pressure looks more likely to rule for quite sometime.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5015043

[bluearmy]

1 minute ago, phil nw. said:

Yes I think so feb.The split today quickly reforms hence the collapse of our block later this week.

It looks like any Scandinavian heights will come from the expected mjo movement and momentum increases.

Good to see Gfs is starting to pick this up.

It could be a downwelling wave from the warming at the end dec into Jan. three to four weeks wouldn’t be outside the expected range. The cross sectional of the atmosphere later may show how the weaker flow comes about through the run. 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5015409

[Eagle Eye]

Just now, bluearmy said:

It could be a downwelling wave from the warming at the end dec into Jan. three to four weeks wouldn’t be outside the expected range. The cross sectional of the atmosphere later may show how the weaker flow comes about through the run. 

Unlikely, the surface patterns seem surface driven and generally the vortex is in a recovery state. Whilst I realise this is the 00Z run, I find this the most likely solution. Wavebreaking is too weak from the major SSW so it won't be that and the reflection from the minor SSW has already happened. 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5015414

[Singularity]

19 minutes ago, Captain Shortwave said:

Worth mentioning that only 24 hours or so ago we were looking at a broad west to south west flow for week 2, then the models are slowly started to make the Euro ridge more amplified and now we have subtle hints that the high could amplify enough to potentially establish a blocking high to the east or potentially even north east of the UK. 

Should trends continue, this will be one of the clearest demonstrations I can recall of how the AAM/GWO diagnostic tool in conjunction with MJO forecasts plus experience of model behaviour can be used to anticipate model bias of the sort that sometimes points entire ensemble suites in the wrong direction.

Could it possibly go that smoothly with a high established over Scandinavia by the end of the month… plausibly, yes. Not that I’d go as far as betting on it just yet - the road has a habit of being rocky UK & Ireland-wise, narrow lands as we are!

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5015661

[Jordan S]

An increased chance of severe gales effecting the country then following on from my previous post, and as others have pointed out recently, a stormy day possible on Sunday and possibly into early Monday as we see a low pressure system rapidly intensify over the North Atlantic before moving northeast across the the uk, most weather models show the centre moving into Scotland, the location of the strongest of wind gusts seem to vary a bit each model run as is entirely expected at this range but the current UKMO, ECM and GFS runs seem realistic and close to what will happen on Sunday with a high likelihood of very strong winds widely for most or all of the UK, but it looks like particularly northern UK will bear the brunt contrary to my previous post highlighting southern and western areas at high risk for severe gales and heavy rain.

breaking it down slightly with current interpretation of most likely realistic scenario..

Central/Southern UK turning very windy on Sunday with widespread 40-55mph gusts likely with some locally damaging gusts of 60-65mph possible even here.. more detail on what may increase the risk of those top gusts.. towards the end of post.. 

For northern areas especially Northern Ireland and parts of northern England and western Scotland, there’s an increasing likelihood of damaging and disruptive gusts quite widely, not just in exposure but inland too. Widely potentially damaging gusts inland of 65-75mph seems quite likely for many northern parts of England, Northern Ireland and parts of Scotland, but some extremely strong gusts of 85-90mph look increasingly likely in a few coastal locations in these areas, if you where to put a percentage on the likelihood of this occurring then (40-60%) seems appropriate for a few coastal areas of western Scotland and perhaps western coastal parts of Northern Ireland. 

 

Heavy rain across many areas, a squally front looks likely to move southeast across England and Wales, and this is where the strongest winds for England and wales will reside, gusting up to 65mph possibly for a few inland, a wave may develop on this, slowing the fronts clearance from the south possibly causing localised flooding in places with upto an inch or two of rain for some. 

Thereafter another wet and windy spell for many later next week although less so than Sunday/Monday. 

For the last few days of January it looks to remain unsettled in the north with hill snow in the north at times, changeable in the south but some dry days here more often than northern areas as is usual, high pressure looks to centre further south than Gfs indicates I think, temperatures look to be slightly above normal for the most part but perhaps turning drier more widely along with temperatures falling once again at the end of January and beginning of February with high pressure over the uk or close by with increased frost and snow risk by early February..

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5014974

[Mike Poole]

14 minutes ago, Jason M said:

They are going mid lat route. High sat over say Germany / Low Countries. I think they will be right. Just cannot see a genuine high lat block setting up.

The question is how do you get to a high lat block from where we are now.

9 minutes ago, AO- said:

I disagree with you for only one reason. I don't see the pv part over Canada Greenland weakening the next two weeks. This means that proper WAA leads to a block in a favourable position (Scandinavia) The only question is how long it will take for the cold to arrive as the cold is pushed back across the Urals the next week. This is the only possibility I see for winter. I could be wrong though, but this option just seems very likely to me. 

I agree with this.  I think what we need to ask ourselves is, given the models were showing a rampant zonal pattern indefinitely, what is the first sign on the models likely to be - if the ultimate destination is a high lat block in Scandi, the first thing we will see is a mid lat block pushing north into the UK, pushed up by WAA from the vortex.  If the vortex doesn’t relent, that should continue and drive the high to our NE - where exactly we don’t know, but a Scandi high looks a reasonable aspiration from there, given a more amplified pattern is expected from teleconnections.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5015550

[Mike Poole]

ECM clusters T264+:

Cluster 2 shows the heights into Scandi evolution, 17 members, some leap still to turn that into a full Scandi high, but it’s a strong signal in that direction.  Cluster 1 heading the same way with a slower evolution.  Cluster 3 remains westerly.

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5015700

[Scott Ingham]

Just now, Battleground Snow said:

I can only see the signal accelerating, similar to how the zonal spell got brought forward.

Doesn't mean the orientation will give us deep cold straight away, but it will definitely be an option at least.

Maybe a holding pattern of chilly weather in the final days of January, followed by something more substantial into the first week of February?

We’re at a decent base state in GWO already. For me because of that once we get a boost in AAM from the +FT and +MT it could be enough poleward momentum to create high lat blocking but in Iceland/Scandi where both the Strat and Trop look better places for a high lat block to set up. The last piece in the budget jigsaw will be the MJO on the 30th of Jan. This will do two things. Strengthen northern blocking and act as a retrogressive signal to Greenland around the 10th with lag. There is a scenario where without the MJO we don’t see enough rise in +AAM and we go with a mid lat block around the UK then retrogressing to Greenland. For me they are the two scenarios on the table. A quicker and longer lasting spell or one that starts around the 10th from Greenland after a UK high

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5015930

[Cambrian]

Over the last day or two we’ve begun to see some very interesting charts in FI, but it’s worth emphasising the exceptional degree of build in heights that will “cut it” for a Scandinavian high far enough north to bring a surface easterly flow and cold into the UK and Ireland, and the kind of build that might look quite impressive on the charts but won’t cut it. 

All taken from yesterday’s output - 

First of all, builds that are not quite there, i.e. some that won’t cut it….

12z ECM ensemble mean at day 10, good build of heights but clearly too far south. Euro high.

 

12z ECM op at day 10, very impressive northward push of heights…

 

…even 12z GEFS at day 14

 

So don’t let the anomalies tease you! Both attain heights over southern or central Scandinavia, with the PV centred over Greenland, and even though the trough is angled favourably north-south, this setup is still not good enough, the trough is too far east in the Atlantic and at the western periphery of Europe we are again pulled into an Atlantic flow. 

Some that will cut it (this type of output is what I’ll be looking out for)…

12z GFS at day 16

 

PV centred to the northwest of Greenland, trough heading down further west into Newfoundland, very strongly anomalous heights over the far north of Scandinavia into the Barents Sea / Arctic Ocean, allowing lower heights to pool over Europe that can bring us into a long fetch easterly.

Now something like that should do it nicely! However, it is an exceptional and relatively rare setup with just the right amount of PV energy needed in just the right places to pull it off. 

Moreover, we are in exciting times where it is possible to connect atmospheric developments over the Pacific with weather patterns on the other side (our side) of the world. 

The trick is to temper our expectations of these teleconnections, and their advanced interpretation in these pages, with respect to their translation to the weather in our local geographical regions, and outside our even more local windows. 

The level of self and mutual congratulation is at times far too high as is the level of criticism by others of those learned and brave enough to give it a go and share that with us. If there is one place on the planet where those delicate intellectual balances can be struck, it is this forum. 

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5016288

[LetItSnow!]

GFS once again showing a nasty windstorm for Sunday. It’s slightly less intense and a little more south with the strongest of the winds compared to this time yesterday but still packs a punch. These are moisture laden southwesterly winds so there will be plenty of rain. Sunday indeed looks to be a day to stay at home if you can with very strong winds and torrential rain. Not the most welcomed after such a long, wet period. “At least it will be mild” with temperatures in the 8-12C range. 

The GFS 0z shows an imbedded low on Monday the 22nd so further heavy rain likely. We import less mild uppers and while the raw data is suggest 2-3C maxes for some reason, I imagine more around around the 7-10C region and a bit higher in the extreme south.

Weather enthusiasts of a cold persuasion may want to look away at the 23rd. A positively balmy flow of exceptionally mild southwesterly winds. More heavy rain will be associated with this, time time more in the northwest. Temperatures look exceptionally mild. Raw data shows 13-14C in multiple spots but I wouldn’t be surprised if 15-16C was reached, couldn’t even rule out 17C. 

However, by the 25th the idea is toyed with yet again for a raise of pressure from the south which will introduce settled and more normal temperatures, particularly if the ridge builds high enough for clear nights. There is the suggestion that the mild weather, at least for the south, may not last too long. Now exactly what the high does afterawards on this run isn’t of too much importance in terms of exacts, though it does show the signal yet again for height rises over Scandinavia. This is important as there does seem to be a signal that this could be our next chase. 

There’s no guarantee of this happening and not every model agrees but with telecommunications favourable I do think it is a possibility that this could just be an unfortunate spell egged on by an intensification of the Atlantic flow due to extreme, record breaking cold in America, and that the building blocks could be in place for a cold set up to return and this could be how we get there. Not anything Id like to make a bet on, but there *is* a signal even if it’s not unanimous… yet!

Hope this was informative as I’m still a novice forecaster!

Original post: https://community.netweather.tv/topic/99760-model-output-discussion-colder-but-how-cold-and-for-how-long/?do=findComment&comment=5016171

[WYorksWeather]

The near-term mild signal is increasing again on tonight's GFS, looking at London. Focusing in on the 23rd, the mean now gets to above 12C. Median would be nearer 13C. And just to show how ridiculous things could get, the GFS P01 is the most extreme outlier I've yet seen. The temperature at midday on the 23rd reaches 16.8C in London. Not only would such an outcome absolutely destroy the daily record, it would even put the all time January record of 18.3C at risk if the model did under-estimate the temperature as it is known to do on occasion, or if somewhere outside London was fractionally warmer.

How's this for an Iberian high:

And here's the resulting temperature map:

I mean what can you say to that other than that it's just extraordinary. 12C up to Yorkshire, 14C almost everywhere Midlands south, and 16C in London.

Again, not likely to happen as it's still at the top of the ensemble and out on its own. I still think the more realistic scenario is we see a raw 12-13C, and probably fall just short of the daily record of 15.2C with something in the 14s. But it's still absolutely extraordinary to even see things like this being modelled as possibilities.

And once again, the most likely explanation is the warm sea surface temperatures near the Azores.

As we go on through the rest of winter and early Spring, worth watching out for any more of these kind of scenarios. The ingredients are there for something exceptionally mild with those kind of sea surface temperatures.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5016897

[Eagle Eye]

I'll be using the 12Z mean because I can't be bothered for the 18Z one to fully roll out except for the reanalysis.

It appears to me that the combined reflection, MJO phase 1 and high GLAAM led to our eventual pattern but the late strengthening of the S.D. of the phasing and the wave reflection being late to the party meant it was delayed quite significantly looking at the pattern. I remember it was modelled to be around the early part of January then the GFS picked up on the signal to delay it for a week or so late December for some reason.

The actual response makes sense, whilst a delayed response and hence the phase 2 response quickly forced the pattern towards a zonal disposition despite the slightly favourable momentum perhaps built-up over the north Atlantic though it was falling, I suspect. As we move towards phase 2 and 3 over the Indian Ocean and an between phase 4, the zonal pattern is favoured and that can be hard to not get stuck with for a while. Especially as the Greenland pattern seems to be moving towards a complete flip which is harder to get rid of than a high there.

As you can see there is some forcing for the potential east Scandi high type that could be forced later on into the output however, it's still favourable for a zonal flow because there's not much energy going into actually forcing it polewards. So, we'll probably stay more zonal with a loaded Greenland pattern and no mid-Atlantic ridge either.

Then, as we move out of phases 2,3 and 4's response, we go towards a phase 5-6 phase supportive for rising GLAAM and the tropospheric forcing poleward to displace andor separate the zonal jet becomes a possibility both in MJO and GLAAM responses aiding poleward forcing of a RWT in certain areas. I suspect what we're seeing now towards the end of the charts. That appears to be helping the weakening of the Greenland high signal w/+VE anomalies leaking over the north and once that +VE wave exits the zonal jet part of the USA w/the rising AAM, it could force towards Greenland stronger than the mean would see it to further weaken the state. Then, the Alaskan ridge becomes more Alaskan centred again and so takes over late January potentially aiding a Greenland high setup proper, which is slightly favoured early-mid February before there's no real signal at all but that's quite far off to be that bold and it could well be a Scandi block instead.

So as we go towards that phase 6-7 that appears fairly likely, it becomes about how much momentum is input, which at the moment seems to be similar to what forced the Greenland high, then about how the response to that is and when. Will be interesting to see. Also, a very possible Strat driver with an omega block over the Ural area favoured on both phase 6 and 7. The Alaskan ridge losing energy is a possible sign of a displaced vortex over North America or split if that Ural wave can happen, more favourable towards a good zonal response here either reflection or SSW wise. That's a bit of a reach this far out but would be a 4th warming if it did occur according to Simon Lee (1st warming upper Strat based, 2nd being the one that caused the reflection, 3rd being the expected weak major or fairly strong minor warming occurring over the next couple days with little surface response I suspect and 4th being this one if it could happen) and would be impressive to see in and of itself.

Then going beyond the rising AAM over the next couple days, there's a weak frictional torque response slightly before another +VE mountain torque event significantly which has been supported on the last few CFS runs, is very possible probably in response to phase 7 and so is that the signal for the +VE EAMT event forcing a very strong Omega block for potential Strat vortex weakening or reversing, very possibly. However, it's a 4 member run and is mostly deviated because the 2 large +VE EAMT events on those members are very significant so it's 50/50. However, does seem that a +VE EAMT event is likely, member 3 has it and member 2 just appears to be slower to move towards it.

What would that high orbit GLAAM combine with? A late Winter phase 8 and phase 1 potentially given the MJO seems to be probably going towards them by that point. However, the strength of those phases is quite hard to predict this far in advance. We'll have to see. Winter is far from over yet though.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017354

[Met4Cast]

I know some are downbeat about this current colder period due to the lack of snowfall (in southern areas, anyway) but the teleconnections advertised this period very well. 

This current cold spell isn't over yet but already it seems a return to blocked/colder conditions is the broad direction of travel into February. The mechanism and drivers for this to occur are already in motion. 

The MJO looks to progress through the Maritimes into the western Pacific, with this frictional torque has risen with +MT following on behind. MT always follows FT. Westerly momentum is transferred from the earths rotation into the atmosphere and the response is AAM tendency goes up, driving total AAM upwards. Indeed, AAM tendency has recently turned positive once again in response to the MJO progression eastwards.

As the MJO continues into phase 6 (and possibly 7, this is more uncertain) we see a configuration favourable for high latitude blocking. It seems probable we'll see a period of mild (perhaps exceptionally so) weather as high pressure builds northwards through the UK but there is an increased likelihood of Scandinavian blocking & thus, colder easterly winds 6th - 15th February as a broad timeframe.

The starting pistol, to borrow a phrase from Tamara has been fired. NWP modelling isn't quite in range of this period yet however we're already seeing signs of pressure rising to the NE via a route through the UK, I suspect these runs are a little progressive in terms of timing but do advertise the broader direction of travel. 

Eyes down.. the next chase is about to begin.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017688

[Met4Cast]

2 minutes ago, Gary L said:

I'm not an expert in background signals but it seems there's far too much emphasis placed on them. I'm assuming they tip the balances by a few % in the direction of some scenarios (e.g. HLB). 

Comments like this confuse me and I think it's down to a lack of understanding of "background signals" that trigger it. The teleconnections are what drive our weather and create the weather patterns that we see, NWP modelling is based entirely upon these signals. Understanding teleconnections allows you to view NWP modelling in a much broader context. "Too much emphasis" absolutely cannot be placed on the things that literally drive our weather. If anything, not enough emphasis is placed upon them. 

I think where people get caught up is that they expected certain drivers to produce specific weather conditions outside their front door & unfortunately, that's not how it works. You can use these drivers to get a flavour of the broader, global scale weather patterns but the micro scale, i.e outside your front door is so local & isolated compared to the northern hemisphere that x + y does not necessarily = a snow day. 

This current cold period & blocking spell we're in the middle of was well advertised weeks in advance. The MJO cycling through phase 1/2 and slowly through 3 helped to generate a Rossby wave packet within the Pacific which led to wavebreaking in the Atlantic & the Greenland high that has brought about the current cold weather. This, in conjunction with a high total AAM state (increased westerly momentum within the atmosphere) led to a perturbed and amplified jet stream capable of generating the HLB we've seen. 

A strong +EAMT (East Asian Mountain Torque) event created the Pacific jet extension which developed a downstream trough, causing a jet streak which then created a downstream trough, follow this all the way into the Atlantic with each "wave" amplifying the next. We've got a Greenland high, we've got cold weather across the UK, broadscale pattern? Check. The next step is the micro, i.e small-scale weather systems that may or may not bring about snowfall in specific areas, that's something background/teleconnective signals can never help you predict. 

Ironically, the "downfall" to this cold pattern & the reason for next weeks milder & stormy weather isn't because of a sudden change in background tropospheric forcing but down to the recent SSW. The SSW has helped to displace the Canadian vortex eastwards towards Siberia which has flattened the pattern.  A case of bad timing, again, something teleconnections can never help you predict. 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017705