Model discussion highlights

[Blessed Weather]

26 minutes ago, RainAllNight said:

Silly question, why is the combination of Urals high and Aleutian low so important?

Just to add to bluearmy's reply and for those who fancy some light bedtime reading I'll quote a couple of extracts from the research papers he refers to. My emphasis in bold:

Title: On the Relationship between ENSO, Stratospheric Sudden Warmings, and Blocking.
Major stratospheric sudden warmings (SSWs) are foremost disruptions of the stratospheric polar vortex associated with enhanced upward propagation of planetary Rossby waves from the troposphere into the stratosphere during winter. This paper examines the influence of El Niño–Southern Oscillation (ENSO) on different aspects of major stratospheric sudden warmings (SSWs), focusing on the precursor role of blocking events. The results reveal an ENSO modulation of the blocking precursors of SSWs. European and Atlantic blocks tend to precede SSWs during El Niño (EN), whereas eastern Pacific and Siberian blocks are the preferred precursors of SSWs during La Niña (LN) winters.

Source: https://journals.ametsoc.org/view/journals/clim/27/12/jcli-d-13-00770.1.xml

Title: Blocking precursors to stratospheric sudden warming events
In this paper, we report that 25 of the 27 [SSW] events objectively identified in the ERA-40 dataset for the period 1957–2001 are preceded by blocking patterns in the troposphere. The spatial characteristics of tropospheric blocks prior to sudden warming events are strongly correlated with the type of sudden warming event that follows. Vortex displacement events are nearly always preceded by blocking over the Atlantic basin only, whereas vortex splitting events are preceded by blocking events occurring in the Pacific basin or in both basins contemporaneously. The differences in the geographical blocking distribution prior to sudden warming events are mirrored in the patterns of planetary waves that are responsible for producing events of either type. The evidence presented here, suggests that tropospheric blocking plays an important role in determining the onset and the type of warmings.

Source: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009GL038776

Plenty more papers in the Netweather Research Library.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784045

[Kirkcaldy Weather]

On 04/01/2023 at 15:26, Kirkcaldy Weather said:

This long duration Atmospheric river setup is becoming a fair bit more extreme than myself and those who foresaw such conditions developing in advance expected. 

Hopefully everyone in the bay area and the sierras are as prepared as possible as you'll very rarely read Forecast wording to this degree

So why are those conditions persisting? If we look again at the jet stream (especially top of image) the Pacific Jet still powered up and quite extraordinarily we can actually link the Jet from the Pacific right across to the UK, therefore it plays somewhat of a part in the weather we see possibly for the next couple of weeks 

I'd like to mention a bit more of how weather patterns are interconnected in some shape or form I've posted about this before but it really is useful to see the wider picture of meteorological developments which I think some members tend to either deny, forget or perhaps lack interest which is fine we all have varying degrees of passion relating to meteorology.

Atmospheric circulation - Understanding Global Change

UGC.BERKELEY.EDU

A nice webpage for those learning and I particularly like the sentence 'the atmosphere is constantly in motion.' 

Again I think this is often forgotten especially those folk adamant to chuck whole months and seasons in the bin without backing such statements with charts or discussing in detail, I think some of it is to try upset those of us that enjoy snowy weather most ,but after seeing it for a number of years on repeat you learn to not let it affect your energy  

Worth mentioning the December stats in a number of countries

One that's went massively under the radar is Iceland very impressive minimum temps recorded there 

Denmark also below average 

Over 14 years since Londons snow event in Feb 2009 we've had a pretty impressive number of cold / snowy related events 

Feb 2009, Winter 2009/2010, November & December 2010, Feb 2012, winter 2012-13,

#1 Beast February 2018, #2 Beast Feb 2021 + December 2022

I vividly remember meteorological agency "experts" in the media before 2009 saying snow would become a thing of the past 🫣

Something of huge importance is that both extremes of climate change are acknowledged and , record minimum temperatures and snow records are happening year on year around the world, amazing Christmas snow statistic with over half of the US snow covered 

Focusing more again on the current conditions, MJO phase 5 setting the scene here's the surface temperatures associated with phase 5 

 higher than average across mainland Europe (which extends NE) and colder than average for Greenland 

Voila...  

 

Would fit in the movie San Andreas, sometimes there aren't words to describe the amazing power of mother nature

Sending prayers and positive vibes to those living in the bay areas and sierras.

I've been doing a lot of studying & research and have found very interesting stuff.

I had this saved from a great paper I read years ago about the connection of the MJO and stratospheric warming events. Fits nice with the progression of MJO phases we have had over the last month or so

I've highlighted that we entered MJO phase 7 roughly New Year's Eve 

We are beginning to see the signal emerging that the phase 7 pattern will begin to filter into the surface conditions by weeks 2-3 of Jan

 

Super interesting that pattern matches really well with the 2nd highest percentage from this paper on precursor patterns connecting with SSW events 

Just a moment...

AGUPUBS.ONLINELIBRARY.WILEY.COM

If that didn't link correctly just google search for Classifying the tropospheric precursor patterns of sudden stratospheric warmings

More on the MJO influence on stratospheric warming from a different paper

 

We see a clear connection with SSW's leading to Greenland blocking 

Which would pair with the lagged phase 7 composites from CPC

Another very interesting find from my research is something I wasn't award of, a big connection of the bomb cyclone / Atmospheric river pattern in the Pacific (the pattern we see right now) and SSW's 

"This study provides the modeling evidence that bomb cyclones in the North Pacific can modulate the onset of SSW."

Just a moment...

AGUPUBS.ONLINELIBRARY.WILEY.COM

Again search for A Critical Role of the North Pacific Bomb Cyclones in the Onset of the 2021 Sudden Stratospheric Warming

We also have a bomb cyclone in the Atlantic, whilst not in that study I'd suspect this will fit with that research and play a part in upcoming stratospheric developments 

Potential for another to develop by early next week 

And a continuation of that pattern on the Pacific side too 

A really positive longer range MJO outlook too should a secondary strat warming event be required 

And I found some more info on the dramatically below average December Iceland saw

All in all a VERY exciting period as January unfolds across multiple meteorological categories 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784142

[Eagle Eye]

Signs of a fairly persistent Ural Block in the mid-term as suspected, though for a SSW potential we're looking at a renewed signal beyond Day 8 ish (e.g. extra Tropical forcing for Tropical-Extratropical interactions via MJO + AAM forcing recognition into the +VE heights in the mid-latitudes and translating that energy forcing into poleward WAA for a Ural Block) and that probably won't be picked up well yet. The actual Ural Block signal through sustained Eurasian zonal jet Retraction is especially from the 11th January onwards. That should fall later on as the frictional torque balances itself out but the Ural Block tends to be a repeating pattern when it gets going and the pattern of EAMT events going forwards suggests that somewhat as well. It will by no means guarantee a SSW but at least it increases the chances when associated with an Aleutian low as well.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784266

[Blessed Weather]

19 minutes ago, Mike Poole said:

Yes, I know.  I’m quite possibly putting 2 and 2 together and making 37, but I was reading those papers @Blessed Weather posted about SSW precursors earlier, and I’m wondering if we need to see some high lat blocking in other places/times as well as the Urals to get the SSW signal that the ECM 46 showed last night, particularly if a split SSW is to result.  Anyway, too early to know any of this yet, we could be seeing the lagged MJO effect, we could be seeing precursors to a SSW, we could be seeing both…or it could all amount to nothing…we will see…

But there does seem some new momentum in the model output…towards…what?

Indeed Mike. It's not necessarily straight forward with regard where the best blocking occurs at any one point in time - Urals would be good but other locations can produce the goods - key to impact certainly depending on background ENSO conditions and how long the block is in place. This chart from the second paper I mentioned highlights this (descriptive notes key):

Fig. 1 Notes: Composites of blocking precursors of SSWs for (a) all, (b) EN [El Nino], (c) LN [La Nina] winters, and the composite difference of the blocking precursors for (d) EN minus LN SSWs, (e) displacement minus splitting SSWs, and (f) wave-1 minus wave-2 SSWs. Blocking precursors are identified from the blocking frequency for the [−10, 0]-day period before the central date of SSWs. The blocking frequency is expressed as the percentage of time (over the 11-day period) during which a blocking was detected at each grid point. The number of SSWs entering into the composites is shown in the top-right corner of each panel. Vertical (horizontal) hatched areas indicate regions with blocking activity significantly above (below) climatology at the 95% confidence level as derived from a 1000-trial Monte Carlo test. Note that the detection of a significantly low blocking frequency (p < 5%) in (a)–(c) is hampered in regions where the climatological blocking activity is low.
Citation: Journal of Climate 27, 12; 10.1175/JCLI-D-13-00770.1

Full paper: https://journals.ametsoc.org/view/journals/clim/27/12/jcli-d-13-00770.1.xml

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784258

[MattH]

Morning.

No significant changes really since the last post of mine, the overall evolution remains unchanged, but as some have been noticing on recent runs there is definitely some evidence for amplification to the pattern across the N Atlantic and into NW Europe towards mid-January and beyond that may bring a more seasonal evolution for the time of year, prior and it is simply a case of 'as you were'.

As highlighted in the previous post we have generally seen a reversal of fortunes in terms of upstream developments, including the AAM and that is highlighted well now on the last plot (below) notice how the -ve E'ly AAM anoms through the first half of December have faded away and generally more W'ly anomalies have become increasingly dominant, especially circa 40-50N. Again, all consistent with the usual influence of a general dominant W'ly regime, but one that isn't as entrenched as it can be.

Now, looking ahead and overall, the key period seems to be around the weekend of the 13th and 14th onwards, towards mid-January and beyond. Whether this is related to the weak MJO is clearly very difficult to tell, or whether a simple and natural variation of the pattern. Clearly, we aren't taking about any sort of significant amplification here which leads to a cut off Greenland high, for example and as was expected there is little chance of any sort of Scandinavian height rises looking forward either, in essence the opposite.

What is present though across the ENS is for amplification over the W N Atlantic (ridge +ve 500mb heigh anoms) with a cyclonic pattern over NW Europe (trough -ve 500mb heigh anoms) but of which could bring in some colder air masses from the NW. We can see this on the hovmollers well below.

Just using the GFS ENS as well for a closer look and 1000-850mb thicknesses, if we roughly place where the jet stream would be we can see how the pattern amplifies with time with a sharper trough over NW Europe and a slow decrease in 1000-850mb values as well. Clearly, this is not going to bring nationwide snowfall, nor is it going to suit everyone, but for those looking for a glimmer of hope for some colder, more seasonal synoptics, then this is about as good as it is going to get moving forward.

The amplication of the pattern will be key to how cold it will get, clearly the GFS 00Z run highlights what could happen with greater amplification with more of a direct N or NW'ly flow which would bring about a more noteworthy cold spell, the 00Z ECMWF, for example, shows tempered evolution in terms of cold.

So, overall it is more of the same, more wind and rain looking ahead, but keep a close eye on the pattern towards mid-month for amplification over the far east of Canada and the far west of the North Atlantic and then also keep an eye on how low pressure and the broader trough develops over NW Europe. The further east the trough progresses, while combining with greater amplification upstream and the colder it will get, but for now nobody knows to what extent, but it's something to keep us coldies interested. As for any SSW then the EC Monthly last update is bullish, GloSea is not, but there's plenty of time for change there, but from what I've seen we still need to keep a close eye on early February...

Regards, have a good weekend. Matt.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784434

[Catacol]

First sign of negative anomalies at the top of the strat for a while - trash GFS modelling but good to see nonetheless

I've been doing some more reading around the MJO, and from Riddle et al's 2012 article an interesting pasted graph:

Cluster 4 in their research is essentially a -NAO profile in the atlantic and this graph shows the signficant lag time impacts of each MJO phase in helping support that -NAO shape. Notice the peak significance of the phase 6 to 7 movement and the lag of 10-20 days attached to the peak period of phase 7 influence. MJO passage recently is this:

so given phase 7 passage from 30th Dec to 5 Jan before losing amplitude any benefits from the MJO look to be in the period 10 - 25 January. This paper suggests phase 8 less significant for -NAO than I expected though the paper does not focus on Scandy potential...

Still the GWO orbit is holding up....code for a more Nino wave pattern than traditional move to a flat Nina

and this means a context conducive to yet more amplification going forward. As MattH has correctly pointed out momentum at 40-50N has been on the high side recently

 

but  I do not expect this to continue not least because of the usual wax and wane shape of the wave pattern globally and a fall in momentum at 50N is predicted even without lag MJO impacts. Factor the MJO into the equation and chances increase further.

Finally - the trop pattern as forecast continues to support ongoing strat disruption. I've been looking for wave 2 impacts to appear, handicapped by the withdrawal of the Berlin maps - but here we go. Wave 2 up and running as early as 192

Signal fades beyond 192 but I have no confidence in GFS at range at the moment and am prepared to state that it is incapable of seeing what lies ahead.

Overall weekend conclusion = growing confidence that the westerly misery will abate mid month, that pacific forcing will give us a more settled setup with a chance of higher latitude blocking taking hold....and I am also becoming more confident that a SSW might occur. Timescale difficult - but when Amy Butler takes to Twitter and throws a little log onto the fire talking of late Jan/early Feb patterns of wQBO/Nina split SSWs I certainly would take notice. 

Roll on the NWP hunt for colder charts that will begin this coming week.

 

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784484

[Cambrian]

Looking at it a bit more, the 0z ECM was very helpful to the cause!

The mean T850s drop below the long term average at day 6, then stay a couple of degrees below average all the way through to the end of the run at day 15. 

The control run lies between the op and the mean through to day 10, and the control and op are very similar at day 10 - all show a chilly, cyclonic picture, with a northwesterly flow from southern Greenland to southern Britain and Ireland. Op / Control / Mean.

  

It’s one of those useful runs where the control looks to be hinting nicely at what the op would have shown if it had ran past day 10. 

The control run progresses to this at day 13, a deep depression to the north of Scotland, embedded in cold air - some quite disturbed, rather exciting winter weather being indicated here, uppers around -6 degrees - and still a good synoptic match for the mean.

  

And notice the same Kara Sea heights that the GFS is showing, which will serve to prevent a polar coalescence of the PV and keep the low heights pushing south over Europe - things beginning to come together for a return to something a bit more like winter. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784478

[Catacol]

8 hours ago, Met4Cast said:

The EC46 has certainly thrown up something interesting in terms of a weaker vortex but I think we need to be careful. The warming being predicted on the EC46 is a result of trop-led wave activity deflecting up into the stratosphere. With that in mind, the idea that "strat forecasts are more stable" doesn't really apply here because it's tropospheric patterns that drive the warming. 

Above all else, it's 3/4 weeks away. The EC46 tends to be iffy with strat forecasts beyond week 2. The extended GEFS sees a continuation of a stronger vortex to the end of January with a few members reaching reversal territory mid Feb. It's by no means a done deal! 

Until then.. more mild & at times wet weather to plague our shores. 

True that trop wave driving is creating the interest, but that wave driving is already kicking off. And at 120h - which is getting close to solid pattern accuracy, we have a very clear precursor pattern.

If we were looking only at trop forecasts in 3 weeks initiating the warming more caution would be required. As it is - the attack looks nailed on. The extent to which it can disrupt awaits to be seen. Lagged impacts still too far out for modelling to pick up reliably.

EDIT - BA beat me to it already….old news!

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784186

[Cold Winter Night]

6 minutes ago, Catacol said:

I can’t imagine why they allowed this new GFS to be released - it is clearly more volatile and inconsistent than the previous product and I’m beginning to ignore it completely. Both GEM and JMA better I reckon.

Do we know if GEFS ensemble is also being created using this new GFS? I assume so….

GEFS and GFS are separate products.

GEFS had its last update (v12) in October 2020. However, according to their documentation, the next update they will be merged:

"GEFS v12 is the final upgrade of a global ensemble system separate from the deterministic GFS at NCEP. The next GEFS upgrade will be merged with the version 17 upgrade of the GFS upgrade planned for 2023-2024."

 

GEFS

WWW.EMC.NCEP.NOAA.GOV

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784223

[Mike Poole]

ECM clusters this morning have a lot of options, most with potential, but 6 clusters in each of the later timeframes.  T192-T240:

So clusters 1,2,3 have the fairly potent PM surge, removing euro heights.  Cluster 4 ridges through the UK to scandi, and clusters 5 and 6 (combined 12 members) look rather poor.  

T264+:

Cluster 2 looks the pick with a high near Iceland (also incidentally represented by the control run), heights to NW on 1,2,3,5 particularly.  Scandi-Russian high strong on 1,6 in particular.  5 has high heights N,S,E,W of UK and looks a bit weird - Arctic high to the fore, cluster 4 looks poor, euro heights again there.  

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784412

[lorenzo]

NWP on the cusp of pattern changes now.. some better viewing ahead for those of a cold dissuasion hopefully, i had thought that the November damage to the vortex would have proven to be more 'harmful' and disrupted the internal vacillation, each winter looking at what it does is new, and the rebound from the blocking was rapid, hence the junk charts ( from a cold perspective) since the end of the cold December period. Each year you look at the base and think this wave break could do this and I guess bias creeps in, but the VI period is like death, taxes and Haaland.

VI periods as known - the last few years has seen Nov HLB aggresively  impinge on how these unfold  - leading to eyes on trop kicks. The MJO of course is a trop kick - the AAM / MT cycles are of course a trop kick - however and this is crucial this season and well demarcated, so much depends on the wave guides in existence when these teleconnections play through the RWTs.

We had a disruptive cycle move from lively to flat very , very very quickly - it was not that the MJO was not true it was more that the RWBs were not conducive.

And in that there are fine margins and some proper academia is needed to map this stuff, the latest from Tomer showing WAFz at 100hPa is brilliant and will let us see the real time evol. of these wave trains and where the wave guides move in response to pattern changes. For now this is a watching brief on what the W1 does and it's a decent W1 to test stuff.

 

Re Vortex Internal Vacillation 

 

http://www.homepages.ucl.ac.uk/~ucahjge/paps/matthewman-esler-JAS-2011.pdf

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784926

[Eagle Eye]

Large IVT over the next few days really shows how the evolution of the low's is taking place and will likely bring quite a lot of precipitation to parts of the UK and Ireland especially closer to the Atlantic. However, it's possible that we see a switch to a more Polar Maritime airflow region according to the ECM. 

Clearly, the evolution of how this works is very shaky and relies on the background drivers connecting together to form a large mid Atlantic +VE ridge/blocking. MJO and AAM forcing from the Tropics through the forcing's interactions with more localised energy input in the mid-latitudes will be the main plot for how this ridge develops. The timing of this being almost on the line of still seeing the effects of the +VE EAMT but also so close to seeing the effects of the -VE EAMT rebound with a quick frictional torque balancing out. 

The trouble with using the MJO as a forecasting method is that it's a very generalised tool just because it's general wave packets can be disrupted by the previous wave breaking interactions between the extratropical regions and how they have placed themselves. For example an omega block causing Baroclinic instability with the placement of the Tropical jet and the Rossby packets get sent not where they are supposed to go in other words. The atmosphere doesn't reset every MJO cycle, it keeps moving and interacting with itself and that causes long-term forecasting difficulty. Factor into that having to work out the general forcing for interactions via amplification and the cycling of AAM especially under the current fairly neutral conditions. This is a big difficulty in forecasting given the distribution of energy between the two areas and I suspect there may be other types of oscillation that we haven't found yet as well.

The weak Kelvin Wave spacing towards the regions closer to home e.g. phase 4/5 suggest increasing interactions for mid-latitude blocking forcing towards the mid-Atlantic via forcing from the Equatorial-Tropics area. The general theme for the mid-Atlantic to North American blocking coming from this combined with multiple other factors (hence why it didn't create one when it got there in late December though there was attempted ridging that just essentially had no other backing and so no real amplification) but how tall it gets will affect how things develop from there. That's the main reason why there's such differing outputs, how strong the Kelvin spacing gets and consiering it's usually poorly modelled, it's difficult to understand which one will be correct here, if any...

Meanwhile away from the Trop pattern which isn't my forte usually and the SHAL (Siberian High - Aleutian Low) pattern seem to be working in our favour. In general, looks to be a repeating pattern of re-amplification since the start of Winter really. A Winter that had that repeating pattern for such a long time was a certain 2017-18 one. If we can get a sudden spike in SHAL intensity then that might just do it given the positioning of Wave-1 mid to long-term, a spike in SHAL strength towards the end of January or a similar (ish) time might just actually do it. For now, I remain cautious as that seems unlikely but it's certainly not impossible.

That's all for now as otherwise I'd just be re-saying what I've said before, pattern looking fairly consistent right now. May do a proper update tomorrow and sometime next week if I have the energy left.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784953

[Kirkcaldy Weather]

Very eye-catching GFS run with pronounced rossby wave breaking which is of similar fashion to the setup of February 2018

 

 

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784920

[MattH]

40 minutes ago, Catacol said:

I don't think we need it at all. The time to use the GEFS only and temporarily place the GFS behind the GEM and JMA is now. This new GFS has lost the plot entirely - it needs pulling by its creators and redesigned. ECM/UKMO/GEM/JMA is the current suite combination of choice.

Quick one on this, but 'behind the scenes' this is indeed very much the same commentary at the moment. What has gone into this update of the GFS is bizarre. If we think back to when it was run as a parallel to the previous GFS model, it was doing then what it is doing now and providing wild and unrealistic swings, even at short-lead-times.

Unfortunately because of all the free data that comes with the GFS, has it has done for years, there is sort of an unwritten rule that the GFS is the 'first model of choice' but clearly that isn't the case and, at the moment at least, it isn't being particularly fondly used or respected. Keep tabs on the UKMO, ECM and GEM.

M.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784997

[Catacol]

7 hours ago, lorenzo said:

From tonight's GFS 18 z, image three is WAFz Heat Flux projected..

 

What a brilliant find indeed Lorenzo - Polarwx duly bookmarked. First GIF ever for me - great for learners to see what we mean by the Ural/Aleutian pinch in terms of warming - in this graphic at 100hpa. Need to see it penetrate higher of course, up to 10hpa - but graphics like this tell a story.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4784974

[bluearmy]

19 minutes ago, mushymanrob said:

............ but what i see there , for us, is the 528dam line well north of the uk, and the 546 dam line over most of the uk. despite surface anomalies

That’s with surface slp 1000mb rob. I usually look for the 552dam line to be well south of the U.K. to be in with a sniff of wintry conditions on those mean charts at more than a week away.  As a rule of thumb, you want to see the 552 dam line south of Brittany at least on a general west to east mean flow. Sharper mean troughs change the game though.  We see our most wintry periods when that 552 is through the French/n Spanish border area. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785056

[Cambrian]

This is all very heartening now, some solidly positive indications for getting the trough through to the east of us by the end of next weekend.

0z ECM ensemble mean and their anomaly charts through to day 10, with the corresponding T850s, definitely turning colder after day 6.

  

The build in Atlantic heights looks decisive, that should quieten it down for a while in terms of sending mild air our way, with a northwesterly flow taking hold for a fair while potentially. If the longwave trough sets up into Europe like this, the only path for any lows is from Greenland, mixed in with a good deal of cold air, down the side of the Atlantic ridge, diving southeastwards into Europe. These lows, are in effect, bringing their own packets of cold air with them.

Days 7 to 10 on the 0z ECM op shows one of these, forming over the southern tip of Greenland and heading directly southeast, through the UK and Ireland to Central Europe, with some decent uppers onboard.

 

By day 10, the next low is rounding the southern tip of Greenland and heights are building up through the Eastern Seaboard, squeezing out the Newfoundland trough, to seal the deal with the Azores high. The passage of the low from Greenland to Europe replenishes the longwave Euro trough, the low running down to the base of the trough also draws it back west again to keep us in the northwesterly flow. This looks like the kind of pattern that could repeatedly reload from there. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785090

[Nick F]

4 minutes ago, Drifter said:

Therefore worrying about the GEFS strat forecast at two weeks range is a bit futile. 

We'll have to see what the updated extended EC shows tomorrow. Both EC and GFS appear to have backed off the strong Ural to Kara Sea upper ridge which may have been one of the catalysts, along with Aleutian Low, for models to weaken the strat zonal winds. But now the high modelled in that region north of Russia is a shadow of its former self. Also there is signs of Pacific jet retraction from an -EAMT /  as much lower pressure develops over eastern Asia - this could weaken the Aleutian Low wave driving with time too. So less wave driving from the trop perhaps than was recently anticipated.

But EC, I believe, still has better vertical resolution compared to GFS, so likely better at forecasting upward wave propagation impacts from the trop to strat. So would wait to see with baited breath what it shows tomorrow evening.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785229

[Catacol]

2 hours ago, Bricriu said:

Can we have confidence in the GFS strat output considering how poor its output  has been for the troposphere.? Although the Exeter update is a concern, it must be that Glosea is seeing no signs of a SSW. Is it possible if this is being led by the trop that it might not pick up on a possible SSW yet? I guess as others have said the next ec46 may reveal a lot. 

Correct. Strat forecasting in general terms is a bit more accurate than trop….except when we are looking at a potential strat disruption event that hangs very definitely on trop output. And in that scenario, and supported by the literature, SSW events simply do not get spotted until they are within 2 weeks range, and even then the outer reaches of the 2 week envelope can be very foggy.

We are playing a hobby game based on probability. If there was a forecaster out there who had 95% accuracy at 2 - 4 weeks then this forum would close and we would go about our business bathed in weather certainty. I do find the downbeat gloom of some posts irritating at times because there seem to be some posters who crave snowy nirvana certainty and many who seem unaware that we are constantly riding a 25-1 outsider when we are plotting paths to UK cold. For my own part I nailed the BFTE about 2 weeks out in 2018. Meanwhile the December just gone was an epic forecasting fail as the cold pattern fell apart so the less said about my cold final third call for December the better! In between times some near misses, some roughly accurate calls. Goes with the territory.

But I do think we can work to understand when our horse is at the back of the pack as we turn into the home strait and have no chance….and those other times when we are sitting in third, whip just coming out and with a fair chance of success. We are rounding a bend as we move through this week and the interpretation of those with a bit of knowledge, and increasingly backed up by NWP output, is that we are in the lead pack with a chance of hitting the front for this next phase of winter. We could, of course, fall at the final fence. C’est La Vie.

No change really in the output over the last 12 hours but to keep it relevant I’ll post the GEM 240h for this afternoon. GEM out ahead of the GFS in the stats and I think hasn’t been half bad this winter as a back up to ECM given we don’t get UKMO medium/long output. If ECM shows something similar in 90mins time perhaps the gloomy comments will cease!

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785243

[Eagle Eye]

-VE EAMT event towards next week retracting the pacific jet but the intial state of the PNA and the MJO Tropical forcing, suggests a movement towards a North Pacific trough connecting up with the Aleutian low. This may mean that we see the +VE Ural Block/BK development but also some sort of ridge/blocking over the US to mid Atlantic region and its important where that forms for our Troposphere pattern for late January/early February. Given the forecasting range, its fairly unlikely to be forecasted well yet. Its good that the signal for the Ural Block + Aleutian Low remains.

So Tropical forcing and the development around the Scandi-Ural region will be extremely important going going February but some PM air in the shorter-term is gaining some decent backing.

Clear signs of that strong atlantic +VE heights development and the resultant flow that'll likely bring cold to the UK though how strong is yet to be decided.

Just a short update for now .

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785297

[damianslaw]

Models very much in the same place they were yesterday, ECM continues to show a change to colder and still unsettled by next weekend, with a more amplfied flow, azores high kicked west and we pull in colder uppers and thicknesses from the NW in an unstable polar maritime airflow, trough sharpening and importantly digging into Europe, UKMO trends same way, GFS though not as keen with the amplfication and thus uppers not quite as cold initially but does eventually pull in colder air from the NW, but signs the azores high may not shift as far westwards and therefore less chance of a sustained polar maritime flow.

A word on wintriness, we are hitting the time of year, when you don't need very cold uppers to produce snow to quite low levels, I was out walking around 300m today and there was heavy snow falling, albeit wet, but it started to stick, and this was in not especially cold uppers - the power evaporative cooling. Sub 528 dam air and heavy precipitation can induce snow to low levels quite quickly - to valley level here, alas usually need something colder further south, and slack airstreams.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785401

[carinthian]

On 08/01/2023 at 07:39, carinthian said:

Morning all . Some broad agreement with UKMO chart below at 144t and ECM. Both have a Arctic high in place and a squeeze southward of the polar front. However, the million dollar question remains . Will the UKMO model out at day 10 follow suite and sink the polar trough deeper into Western Europe.?  We all know getting the ideal snow making charts are far from easy especially having the Azores high alignment in the correct place. However, think we are heading for a better place in 7 days time.

C

Aye, its a good morning. First snow for weeks has arrived just in time. Snowing quite heavily with temp of -0.2c currently in the village . A bit wet but its a start. Broad agreement again  UKMO/ECM for next week with some advance of the polar trough through the British Isles. Of course , alignment of the Azores high crucially important going forward. A projected powerfull NWly jet to develop later next weekend in the vicinity of NW Europe will have an impact on positioning of the Atlantic high. Looks like UK and much of Western Europe will be on the colder side of the jet for atime and could be open to some quick sinking low formations  to develop  on its northern flank. The movement of the high does not look static and will ebb between lateral and retrogressive pole ward. So potentially some fast changing weather on the cards and snow likely to feature in the forecasts later in the week. However, will the squeeze on the polar trough be sustained going forward 168-240t ? Thats the million dollar question and only the behaviour of the Azores high has the answers ! Anyway, overall quite pleasing charts on offer this morning, especially welcome here in the snow starved Alps.

c

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785712

[johnholmes]

Giving my view on the 500 mb anomaly charts

The far west keeps the trough-ridge off the west coast-just inland of n America, been there for days it seems. This runs into the major winter trough, quite rounded, centred over ne Canada, then into a broad westerly over the Atlantic into the UK and western Europe. What has changed is the sudden appearance of a fairly high +ve anomaly off eastern Canada, and a very slight sign of mid Atlantic ridging, along with what has slowly been evolving –ve heights to the east and ne of the UK. This has now got the slightest indication of a trough, shallow and broad over western Europe. These developments suggest, no more at the moment, that a slight veer in the overall flow over the eastern Atlantic is going to develop. This would tend to give a slightly colder pattern of Pm air over much of the UK rather than just the northern half of Scotland. Another couple of days ill make it clearer just what pattern we end up with; just as described or a marked meridional pattern. Currently about 30% for that I reckon.

Checking the ECMWF 10 day output and it shows a wnw-nw 500 mb flow and a surface feature to the n or ne of the uk. The 850 mb -5 C does largely remain well north with a 2 day foray into northern England. So both models show a trend of a veering surface and upper flow but no major deep cold air.

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

The 8-14 is pretty similar to the 6-10

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785719

[mushymanrob]

12 hours ago, Allseasons-si said:

Oh come on John you tease ha ha,...spill the beans me old lad

i do see on the NOAA charts that the trough migrates a little more towards Scandi in the ext'd and also lowering the heights into Europe,...is this what you are maybe implying?

 

As i see it, theres a strengthening azores high  thats nudging towards us. How far East it eventually gets is unknown yet but the EPS for the 22nd (has been posted) suggests continues Eastward.
To me the main features are the Azores high and the trough over Baffin Bay, which between them are driving the jet stream across the UK. We may well get PM shots as John mentions , but with that trough over Baffin and the Azores high in place, theres no easy route to anything Wintry there and this synoptic picture is not one cold lovers want to see developing. The closer the AZH gets, the milder its likely to be as long as we keep the Westerly upper flow. So whilst the pressure anomalies are in place for cold, that strong persistent Westerly upper flow will prevent any proper cold for more than 36/48 hours tops.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785733

[Kirkcaldy Weather]

On 06/01/2023 at 17:53, Kirkcaldy Weather said:

Would fit in the movie San Andreas, sometimes there aren't words to describe the amazing power of mother nature

Sending prayers and positive vibes to those living in the bay areas and sierras.

I've been doing a lot of studying & research and have found very interesting stuff.

I had this saved from a great paper I read years ago about the connection of the MJO and stratospheric warming events. Fits nice with the progression of MJO phases we have had over the last month or so

I've highlighted that we entered MJO phase 7 roughly New Year's Eve 

We are beginning to see the signal emerging that the phase 7 pattern will begin to filter into the surface conditions by weeks 2-3 of Jan

 

Super interesting that pattern matches really well with the 2nd highest percentage from this paper on precursor patterns connecting with SSW events 

Just a moment...

AGUPUBS.ONLINELIBRARY.WILEY.COM

If that didn't link correctly just google search for Classifying the tropospheric precursor patterns of sudden stratospheric warmings

More on the MJO influence on stratospheric warming from a different paper

 

We see a clear connection with SSW's leading to Greenland blocking 

Which would pair with the lagged phase 7 composites from CPC

Another very interesting find from my research is something I wasn't award of, a big connection of the bomb cyclone / Atmospheric river pattern in the Pacific (the pattern we see right now) and SSW's 

"This study provides the modeling evidence that bomb cyclones in the North Pacific can modulate the onset of SSW."

Just a moment...

AGUPUBS.ONLINELIBRARY.WILEY.COM

Again search for A Critical Role of the North Pacific Bomb Cyclones in the Onset of the 2021 Sudden Stratospheric Warming

We also have a bomb cyclone in the Atlantic, whilst not in that study I'd suspect this will fit with that research and play a part in upcoming stratospheric developments 

Potential for another to develop by early next week 

And a continuation of that pattern on the Pacific side too 

A really positive longer range MJO outlook too should a secondary strat warming event be required 

And I found some more info on the dramatically below average December Iceland saw

All in all a VERY exciting period as January unfolds across multiple meteorological categories 

Today + Tomorrow seeing the most extreme of the Atmospheric river conditions so far

Day 1 Valid 12Z Mon Jan 09 2023 - 12Z Tue Jan 10 2023 ...A MODERATE RISK OF EXCESSIVE RAINFALL CONTINUES ACROSS A LARGE PORTION OF CALIFORNIA, INCLUDING THE BAY AREA AND MUCH OF THE CENTRAL VALLEY... ...NUMEROUS FLASH FLOODING EVENTS LIKELY, SOME POSSIBLY SIGNIFICANT, ESPECIALLY OVER BURN SCARS... A more significant, elongated Atmospheric River (or AR) event is already beginning to impact much of CA ahead of a more amplified upper trough, effectively tapping into the subtropical regions of the north Pacific. Guidance continues to show PWs climbing between 1.25-1.5" (highest along the coast, and easily surpassing the max moving average per OAK and VBG sounding climatology), with southwesterly 850 mb flow peaking between 60-70 kts. Low to mid-layer moisture transport will be quite robust, as the 850-700 mb moisture flux peaks at 5 standard deviation range above normal, per the GEFS. Meanwhile, some elevated instability (at least 200-400 J/kg per the ECMWF, GFS, and HREF mean), along with the degree of deep-layer forcing and moisture, would support peak hourly rainfall rates of 0.75-1.00+ inch (especially within the Moderate Risk area). Overall, guidance consensus remains quite good with respect to the QPF, with 24 hour totals between 2-4+ inches over most areas (along with pockets of 5-8+ inches along the coast-coastal ranges and across the western slopes of the Sierra Nevada). This will be a fairly significant event as far as ARs go, with the latest deterministic QPF indicating a 5 to 10 year average recurrence interval (or ARI) within portions of the Moderate Risk area. In addition, the latest HREF 40km neighborhood probabilities of 3 hourly QPF exceeding current 3 hour FFGs climb to >50% within the Moderate Risk area after 15Z Monday. Considering how wet the soils will be ahead of this event (over the 90th percentile within the top 100 cm across the majority of the outlook areas per the latest NASA SPoRT), impacts from flash flooding or more rapid inundation will become increasingly likely -- especially across the several burn scars since 2020. Churchill/Hurley Day 2 Valid 12Z Tue Jan 10 2023 - 12Z Wed Jan 11 2023 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHERN CALIFORNIA... Maintained a Moderate Risk area for excessive rainfall across portions of Southern California. Models continue to indicate a distinct southward shift in the QPF maxima on Day 2, with significant rainfall already expected to be ongoing Tuesday morning across upslope portions of the Transverse Ranges (with as much as 3-6" having already fallen on Monday and Monday night). Long duration of southwesterly flow will allow for another 2-4 inches of rainfall (locally) along the terrain on Tuesday, with precipitable water values of 1.00-1.25" and the chance for thunderstorms as low-level lapse rates steepen (and ML CAPE reaching perhaps as high as 500 J/kg). Areas along the coast and in the valleys will receive closer to an inch of additional rainfall on Tuesday, coming with an additional (final) surge of tropospheric moisture (and eventual cold front passage) in the afternoon.

We see just how much outside of the climatological norm this amount of rain and snowfall is 

Also rare severe thunderstorm Day 1 + 2 outlooks for California with tornado risks 

 

Brings my mind to this 

Ended up being an impressive bomb cyclone in the atlantic with a 51mb pressure drop in 24hrs

We continue to see the MJO phase 7 & SSW precursor pattern playing out 

 

There has been a taboo around displacement events being associated with failing in bringing cold and snowy conditions to the UK however this is misleading, interesting results from this paper

"Key Points

Little difference in the longer-term (3–4 weeks+) surface response in either free-running or thermally forced displacement and split events

Conversely, large differences are apparent between displacements and splits at shorter lags

Displacements yield stronger stratospheric temperature anomalies than splits yet still give rise to similar-magnitude tropospheric responses"

'For instance,  at 60 N and 10 hPa clearly shows a weaker vortex for the displacements than the splits'

A tonne of reading in it but an excellent study  

Just a moment...

AGUPUBS.ONLINELIBRARY.WILEY.COM

Google search - displacement stratospheric warming, its the first paper from 2021

More reason not to fear displacement events, again we see the clear link of strat warmings and Greenland blocking 

 

Images from a useful thread by James P 

Initially the current signs seem more toward a displacement (this could still see a split further down the line) taking the JMA which shows that nicely 

We currently have a bit of warming taking place 

And note how the PV gets shunted away from the Arctic southwestwards 

 

Oh did you think that was it... nah we have the next EAMT event shaping up too 

I did mention weeks 2-3 of Jan would be exciting

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4785800