Model Output Discussions 12z 01/09/2016

[SMU]

14 minutes ago, blizzard81 said:

I am expecting the.opposite. I think November will be very unsettled. Not especially mild but not cold either. Little or no blocking and very mobile. The blocking will re appear in Dec though :-)

You could be right

Nov 09 & Nov 12 saw a pattern relaxation in November ( although both months AO came in slightly negative )

S

[shaky]

Gfs 06z at 192 hours looks a beauty!!if only 4 weeks down the line this place would be buzzing!!a nice icelandic high on this latest run!!

[phil nw.]

Yes the ens have been pointing the way for some days towards the main high moving across towards Iceland and pressure falling gradually over Scandinavia.

Another look at the Icelandic pressure graph shows this peaks around mid-month with signs of it then just starting to fall away.

 

 It's still looking quite dry and quiet pretty much nationwide.We can see from these 2 rainfall graphs- for C.England and C.Scotland how little rainfall is expected.

No signs yet of  an awakening Atlantic jet although i am watching carefully where we might go after mid-month.Usually towards the end of October pressure up there over Iceland and Greenland starts to fall away dramatically and any heights are usually pushed south with the jet kicking in over the top bringing in a more mobile westerly pattern.

 

 

 

 

 

Edited October 7, 2016 by phil nw.

[Frosty.]

The Gfs 6z doesn't show the Atlantic returning until over 2 weeks from now, in the meantime the scandi high dominates and eventually it drifts northwest as heights lower to the northeast and we get some chilly NEly winds with temps barely reaching double digits celsius and some wintryness across the scottish mountains with some night frosts..very seasonal and who knows, the Gem 00z is still possible with retrogression being the theme of the 6z. 

[knocker]

Yes the 06Z indicating the start of the breakdown.

[Frosty.]

4 minutes ago, knocker said:

Yes the 06Z indicating the start of the breakdown.

Yes, in 15 days..plenty of water to go under the bridge before that possibility.

Edited October 7, 2016 by Frosty.

[Nouska]

For anybody worrying about what monthly or seasonal forecasts show now - what about this turnabout in one week!

Below are the SE European tmax projections from the EC32 last thursday and the new update today. Focus on week commencing 10th October.

    

[Severe Siberian icy blast]

3 minutes ago, knocker said:

Yes the 06Z indicating the start of the breakdown.

Lol knocker at t324 ??? Not that old chestnut again !! In the mean time . A tanking negative AO/NAO (probably)for the next 10 days at least! 

[johnholmes]

5 minutes ago, Nouska said:

For anybody worrying about what monthly or seasonal forecasts show now - what about this turnabout in one week!

Below are the SE European tmax projections from the EC32 last thursday and the new update today. Focus on week commencing 10th October.

    

A pretty impressive turn a round over much of the chart. Just goes to show that longer term is pretty fraught be it from a model or any other source

[Frosty.]

1 minute ago, Severe Siberian icy blast said:

Lol knocker at t324 ??? Not that old chestnut again !! In the mean time . A tanking negative AO/NAO (probably)for the next 10 days at least! 

Yes, in deepest lala land ( 2 weeks ) the atlantic struggles to make inroads..lots of chilly weather to come.

[daz_4]

5 hours ago, MR EXTREMES said:

but the reason im upbeat is because we already have a sustained pattern in place

Question is though, will this pattern hold? The change happened very quickly and it can flip back as easily. I mean look what models showed on 26.9 for this week.

I don't how it is in UK but the last really cold month here was March 13. Since then 34 months were above average (9 of them with deviation 3C degree or more), 6 average and only one! below average. Would be definitely nice if this warm period finally came to an end but we've had this short cold blasts in the past three years and they never lasted. I'm therefore cautious whether this will be somehing long term or not. It can be very quickly forgotten if the warm air floods Europe in November and December. Let's hope it does not happen  

[Mucka]

3 hours ago, fergieweather said:

00z EC clusters generally lean similarly towards end of Oct (towards a resumption of mobility), much as GloSea5 has done for a while now. However, any such transition - whenever it materialises - will doubtless prove complex/messy. It'll thus be interesting to see if any further hint of blocking for November appears in tomorrow's EC Seasonal update, or whether it switches to something more mobile/zonal.

 

This is definitely what most interests me.

Yes as people here have said, there is nothing unusual about mid lat blocking appearing in Oct but the readiness with which the pattern appears to want to retrogress and positive height anomalies push into Greenland is quite unusual, but still the really interesting part for me is the, "what happens next?" as we move into the last 3rd of Oct.

There are signs of a decline in blocking but it is out in FI and even where the shorter range GFS and its ensembles go along with this decline there is no sign of a flat Westerly jet or bog standard zonal pattern setting up which may be a sign that they are indeed just returning to climatological norms in absence of any strong overriding signal at that range. This is why I will be most looking forward  your update tomorrow.

My instinct (or is that rose tinted spectacles?) tells me that, after a fairly brief and messy breakdown of blocking,  high pressure will want to rebuild, probably over Scandinavia but whether that is wishful thinking or not a fairly quick return to dominant blocking would definitely raise eyebrows - not least because the cold over central Eastern Europe would remain largely intact and the PV would likely be struggling to get organised. 

 

 

[Polar Maritime]

Let's please continue with constructive Model discussion, Thanks.

[joggs]

2 hours ago, Nouska said:

For anybody worrying about what monthly or seasonal forecasts show now - what about this turnabout in one week!

Below are the SE European tmax projections from the EC32 last thursday and the new update today. Focus on week commencing 10th October.

    

Sorry for not understanding fully.Could somebody pleases explain the above.Thanks.

[northwestsnow]

Well GFS12Z is very very dry for the next 10 days or so, high pressure never far from the UK, no sign of the vortex getting its act together, yet...

[swfc]

hmm the 12z looks like the high could be under the cosh tbh.looking like the iceland- greenland retrogression is not happening ?early days tho granted

 

Edited October 7, 2016 by swfc

[knocker]

17 minutes ago, joggs said:

Sorry for not understanding fully.Could somebody pleases explain the above.Thanks.

The two charts of SE Europe from two ECM monthly runs a week apart for the same time frame illustrating the switch to very cold air as can be seen by the preponderance of blue in the later run which indicates the switch to cold anomalies.. They are not the easiest charts to read for detail but that isn't really necessary.

Edited October 7, 2016 by knocker

[Frosty.]

This is what I'm looking for now, signs of an Arctic maritime incursion which given the current model trend of retrogression is quite a realistic prospect, a very encouraging last chart from the Gfs 12z for a taste of the arctic through late october. In the meantime, the scandi high looks very strong and dominates our weather for the next few weeks, it continues to look very blocked for many days to come, there is even some snow on the map which is always welcome!.

Edited October 7, 2016 by Frosty.

[stodge]

Evening all

Plenty of comment on some output which, if this were December or January, with a snow covered Europe, be the perfect synoptics for cold (as distinct from snow). Again, as others have said, anticyclonic weather in mid-October is far from unusual - we had it as far aback as last year. The huge difference between then and now is last year's conditions were based on a ridging Azores HP, a northerly tracking jet and low heights over Greenland.

In 2016, we are in a very different place synoptically. Tonight's GFS and GEM output suggests the current core of HP over Scandinavia will move SW to lie just NW of the British Isles before the attempted retrogression to link to the heights over Greenland opening the door to a northerly outbreak as the trough digs down over Scandinavia. That is the very holy grail for cold fans though it's far from certain at this time.

None of this means much in terms of the winter synoptics - the cynic in me thinks it's unlikely such an unusual synoptic set up could happen again so soon but we do now this pattern can become strong if the right conditions permit. 

Here in the south, we stay under an E'ly flow with variations for the foreseeable future - GFS offers the possibility of some warmer and clearer SE'ly air next week while GEM keeps us in a general E or NE flow.

 

[joggs]

1 hour ago, knocker said:

The two charts of SE Europe from two ECM monthly runs a week apart for the same time frame illustrating the switch to very cold air as can be seen by the preponderance of blue in the later run which indicates the switch to cold anomalies.. They are not the easiest charts to read for detail but that isn't really necessary.

Thanks Knocker.

[Man With Beard]

The cold mafia have certainly gotten access to the GEFS servers tonight, here's an ensemble spread for Scotland for starters:

and a number of runs continue to veer towards this cluster in its latter stages, including the control and op runs - a lot of cold to follow shortly afterwards:

  

However, in the shorter term (D7), the possibility of an interlude in the cooler weather if a low parks itself to our west for a while and the low over Europe stays east.

You'd have to say such a chart would have the potential to prevent the future retrogression of the pattern and introduce a southerly-based flow for longer. However, both the UKMO and GEM are on a completely different page. 

[knocker]

Declining Atlantic HP in the later time frame but still an intense Aleutian low and significant, or not,  WAA,into the Arctic.

[Tamara]

On ‎04‎/‎09‎/‎2016 at 13:03, Tamara said:

The overall ENSO state is not (yet) prohibitive to further enhanced eastward moving tropical convection occurring and some forecasts (eg the Canadian modelling) points to fresh MJO related activity heading eastwards from the Eastern Indian ocean from mid September.

Such an eventuality would spark a further boost to angular momentum and any unsettled phase beyond next weekend, should it occur, perhaps being fairly brief before further potential high pressure into the second half of September. .

 For what it is worth though, based on MJO trends through the summer - which have shown enough eagerness for activity against a relatively benign ENSO state, there are decent enough grounds for anticipating a consensus for another round of convection later in September. So plenty to look out for in the coming days ahead.

Meanwhile, some excellent weather to enjoy for many the coming week  with the further outlook highly uncertain with so many undecided variables waiting to be answered in the meantime

And so this activity came to pass, and despite the SOI index heading a little further into +ve territory to underpin very weak Nina/neutral status, we have seen enhanced cloudiness and convection spilling into the Western Pacific from the Tropical Maritimes regions,. This, allied to Typhoon activity in the NW Pacific, created Rossby wave breaking to underpin atmospheric angular momentum and promote anticyclonic conditions over UK and Europe.

This particular tropical convective behaviour is not typical of La Nina - and its importance in holding generally ENSO neutral/marginal Nina conditions through the autumn takes on greater significance the further we head towards winter in terms of ocean/atmosphere feedbacks. Some generalised comparisons below towards the foot of the post are made with other weak ENSO autumns 2009 and 2012 in this respect

Septembers modestly +ve SOI shows very minor consolidation of a very weak Nina tendency. But at this stage,  still well below the threshold tenure that declares an official Nina base state

https://www.longpaddock.qld.gov.au/seasonalclimateoutlook/southernoscillationindex/

The blue (negative) shading in the bottom map represents the above average cloudiness associated with precipitation as depicted by OLR (outgoing longwave radiation). As stated there is more activity in the Western Pacific than might be expected in a typical Nina and holds interest to watch future similar behaviour maybe during late autumn and early winter.

The European blocking pattern through September came courtesy of a Global Wind Oscillation orbit which was keen to revolve around a narrow framework of mostly low signal Phase 0/1 and a slightly stronger Phase 4 signal - as westerly wind eddies created by the activity in the West Pacific further offset the weak Nina signal, and created the modest amplification in the pattern for downstream ridges across Europe

This pattern reflected well to early autumn GWO Phase 4 composite

Wave lengths are now changing as we head deeper into autumn. Since the turn of the month we have seen propagation of these modest poleward +AAM anomalies to higher latitudes. This process has been augmented through Atlantic tropical storm and especially latterly Hurricane Matthew becoming somewhat trapped within the greater H500 pattern and in the process helped intensify the warm air advection process into the Arctic. Furthermore, taking into account the 2nd lowest sea ice minimum reached in September and also end of summer/early autumn season polar easterly (warm) anomalies being pushed from the polar stratosphere into the troposphere, we see the end product of an anomalously warm September mid latitude Euro ridge give way to a substantial block on our side of the arctic in early October - that has been feeding progressively cooler air westwards through this week. And making quite a contrast to conditions in Southern and Eastern Britain especially where the warmth was most predominant. On the other hand, NW Britain has seen drier and sunnier conditions, albeit not warmer, as the Atlantic troughs have been stopped in their tracks by the block to the NE.

So, it is here where we have to derive caution looking ahead and not extrapolate too much from a current NH H500 blocking pattern that would send this forum into a rabid frenzy if it occurred in 6 to 8 weeks time.

My perspective would be that it would be better to see the vortex attempt to develop through this autumn, flex its legs, but then be prone to snap apart quickly through a combination of effective Brewer-Dobson circulation transport of ozone from the tropical stratosphere to the polar stratosphere and an atmospheric circulation that is keen to repeat +AAM spikes that drive rossby wave trains into higher latitude. Through these mechanisms, ensuring that any early snow cover built up over Eurasia courtesy of October HLB is sustained and advanced further upon to create stratospheric destabilisation feedbacks of their own-  as the winter begins and then progresses into its deeper phase

The alternative scenario is a below average blocked October courtesy of a warm  lower stratosphere/troposphere courtesy prior to vortex intensification. So far so good. But a new season polar vortex that cannot be checked because of the lack of the ingredients as outlined above. On that basis, any HLB in October however appealing it may look at face value, adds up to a hill of beans for the winter season ahead. 

 2009 most especially, but also 2012 had all the vortex destabilisation ingredients in place and meant that cold momentum increased with time rather than flattered to deceive with apparently promising cold blocking synoptics giving way to dominant polar westerlies.

There has been uncertainty regarding the QBO phasing leading into these shorter season, following the curveball thrown by last years exceptional Nino event in terms of sustained +ve (westerly)QBO state. In the Southern Hemisphere early spring, the solar response switches sign between the two QBO states and according to whether we have +ve or -ve QBO phase, this has ramifications in terms of speed and amounts of ozone transport from south to north pole. Ozone concentrations which warm the stratosphere and destabilise/weaken the polar vortex.

The Tropical Stratosphere through the start of Spring (our autumn) has shown temperatures close to the early SH average.

 

Ideally we would liked to see it colder at this important time, so that gradients are reduced as the polar stratosphere starts its own seasonal cool down. The less the temperature gradient between the tropical and polar stratosphere, the more effective is the BDC of ozone from south to north pole. This in turn restricts the development of the new season vortex.

In September 2012 for example we had been ahead with temperatures colder than average through the important early Spring switching time (our September)  Also look how 2011 compared to 2012 at the same time. Much closer to 2016.

In terms of the above discussion so far, we ideally would also be better heading through this autumn with an ENSO state that was inclined Nino/neutral (like both 2009 and 2012) than Nina/neutral. We could also do with better indications in terms of QBO/stratosphere development (or rather demolition) than may be apparent at present. We had -ve (easterly) QBO conditions to assist in 2009 and 2012.

Clearly these are only provisional indicators and much has yet to develop further.  In the coming few weeks, we should look at how the H500 anomalies develop through both the Pacific and Atlantic as we head into  the middle and latter parts of this autumn. We should remember that the current hurricane season which is providing some assistance for warm poleward warm air advection and rossby wave eddies to stir up extra amplification will not be sustained as we get beyond the close of season in November. And it is in November that the new season polar vortex will begin new season development an intensification in earnest.

That on its own places caveats on early autumn HLB's.

Global Atmospheric Angular Momentum (GLAAM) , as already discussed, continues to suggest close to neutral/very weakly Nina inclined parity

So this year looking for decisive signals one way or the other from the ocean/atmosphere circulation is harder. That looks unlikely to change to much extent during the remainder of 2016.  However, the atmosphere may still incline itself one side of the ENSO base state line enough to make subtle differences to upstream and downstream H500 patterns - also depending on how the stratospheric vortex aligns itself.

Notwithstanding all that, the presence of increasing low pressure anomalies though our autumn in both the Pacific and Atlantic will be reminiscent of a more Nino like response from the atmosphere - or more accurately in this case, attempts of the atmosphere to take a slightly de-coupled stance from the neutral/weekly Nina ENSO base state. An increasing tendency for twin Pacific height anomalies and an Atlantic ridge anomaly suggests that closer coupled alignment to a Nina base state is occurring.

Both 2009 and 2012 were ENSO neutral heading through autumn but went on to exhibit the Nino tendencies with a lot of Atlantic troughiness. We saw the Global Wind Oscillation jump decisively through the autumn/early winter in both years to Phase 4/5/6/7 orbits. -part indicative of the significant poleward rossby wave bombardments that were occurring on the polar vortex. The Atlantic troughiness of the autumn succumbed to disruption in both cases from the start of December - and in the case of 2009 as we know, a spectacular change to cold blocking during December.

Autumn 2011 however, had very much the Nina tendencies with a persistent Atlantic height anomaly and jet flowing over it. The Global Wind Oscillation persisted in a Phase 1,2,3 orbit - typical of this regime.  Any cold (er) shots were dependant on temporary upstream amplifications. Autumn/early winter 2010 was an exceptional Nina anomaly with extreme amplification of the Atlantic/southern Greenland ridge and early season vortex destabilisation courtesy of solar minimum. We should not  rely on any La Nina to provide that very rare response this year.  In terms of this years background indicators we are better placed to see as little Nina influence as possible to help sustain any early cold salvos which commonly occur in Nina tendency late autumns/early winter (and should they occur this year). Otherwise early season promise may indeed flatter to deceive. 

The longer range G5 and Euro models as posted by Ian F today are picking up on a signal, that are in my opinion probably echoing new season vortex development and intensification as we head into November. There may also be a small element of climatology bias, but I would not place much (well intended) hope and emphasis on this so close to the start of another stratospheric winter. Especially "if" there is another definitive westerly QBO in the mix.

So better to expect to see the Atlantic coming back and not place faith in the current blocking have any deeper meaning - for the time being at least. The question thereafter is do we head down the early vortex disruption (ad trough disruption) route or the sustained vortex intensification route with a prominent Azores/Atlantic High duelling with a flat and active northern branch of the Jetstream.

This post just puts out some feelers, nothing more. It is not a forecast and I don't make longer term forecasts anyway.

But whichever route Mother Nature takes us, what it is intended to do is put some perspective on the current higher latitude blocking scenario.

 

[Matthew.]

Thank you for your research above Tamara. Very educational understanding the jist of possibilities. The ECM tonight shows the very real possibility of some of us going into a drought scenario(3 weeks with less than 33% rainfall) as even by the 15th high pressure is over the UK. As others have brought out though maybe more unsettled weather could be on the horizon.

[Man With Beard]

Tamara - certainly agree with your assessment that current blocking won't hold back the vortex come November. Kind of why a flukey late October cold shot might ease the pain of cold starvation for the rest of the year! I think there's a small window of opportunity coming up but I'm not expecting it to last more than a few weeks. Indeed, the ECM tonight suggests we may not even get that far.