Model Output Discussion 29th December - Into mid-Winter.

[blizzard81]

Just now, Purga said:

Some decent cold clusters showing in the EC ENS

 

Those are from this morning's run.

[feb1991blizzard]

1 minute ago, Purga said:

Some decent cold clusters showing in the EC ENS

 

That's the 0z - I am hoping for better in 20 mins time.

[pyrotech]

Below is the full reply from ian, posted so he does not get hundreds of posts asking same thing

Personally i think thats sounding very positive  as it seems maybe they are taking notice of same features we are even at that timescal

 

Ian Fergusson ‏@fergieweather  42 minutes ago

@Floodwarncouk models have been toying for a few runs now with broad idea of a more pronounced NW'ly to N'ly outbreak, but still early days

.cont'd... so yes, the likelihood of that has increased, albeit much too early to be deterministic on scope/outcome.

[radiohead]

12Z JMA looks quite snowy at T180...

Edit: Fixed the precip image

 

Edited January 5, 2017 by radiohead

[radiohead]

12Z ECM ENS means has excellent support for the Op at T192

[feb1991blizzard]

The 12z EPS 240 mean not backing the op.

 

In fact its closer to the 0z op than the 12z op at T240.

Edited January 5, 2017 by feb1991blizzard

[chris55]

32 minutes ago, Tamara said:

Probably not the best time to post this and *appear* to burst any NWP virtual bubble over latest operational roll-out with some boring analysis, but nevertheless such that is intended to be objective and useful.

The concerns expressed in the posts of late autumn and start of winter related to breakdown of +AAM/weak Nina disconnect and w/QBO stratospheric tightening through December have come to haunt - flying in the face of repeated alluring NWP ensemble suites which continued, periodically, to tempt many cold weather model watchers right up to the turn of the year. So further (apparent) kill-joy, however realistic it may be, is risked here.

The evidence has been gathering through December to keep harbouring and increasing those early doubts, and some of the latest stats confirm exactly why we are struggling to carve out a consistently sustained upper cold pattern in the UK with a lower angular momentum state establishing and a seasonal vortex which has harnessed the assistance it needed.

The Southern Oscillation Index, in contrast to the ENSO disconnect of autumn, is now steadily accumulating positive figure returns - typical of a Nina imprint on the atmosphere. However weak that is set against a neutral ENSO ocean state.

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

The atmosphere/ocean disconnect process (declining SOI) reversing since start of winter. The disconnect period was when the initial starter destabilisation process on the early season vortex was created

 

Easterly wind/+ve Outgoing Longwave Radiation (OLR) anomalies are evident close to the Dateline in the Pacific - also consistent with the weak La Nina signature that has been evolving through December on the atmosphere. Note also that currently the most organised tropical convection is indicated in the East Indian Ocean - further evidence to point to current lower atmospheric angular momentum state

 

The Global Wind Oscillation has slumped and stagnated back to a very low amplitude and indeterminate orbit phase, consistent with lack of help from the tropics (MJO) to add westerly component to the atmospheric circulation and help amplify the pattern sufficiently downstream to create more sustained and meaningful cold air advection - than attempted topplers

Never to be taken completely at face value anyway and the actual GWO signal is very weak, but this composite for GWO Phase 1 into 2 of mid latitude high pressure ridging extending from Atlantic to SW UK not a bad reflection of short term (to day 5) NWP in terms of height anomaly, albeit troughing across N Atlantic not so clearly in evidence

              

 The question further out is how much amplification is available to enable troughing to dig through Scandinavia along with greatest coldest air advection. To now the coldest upper air has continued to be taken south east through central/Eastern Europe into the Eastern Med, and the UK struggling to tap into more than transitional Polar Maritime air as the Jetstream flows around the Atlantic/Azores Ridge 

Notwithstanding the evenings NWP which has unravelled as I type and suggests what is probably, imo, the very maximum and temporary bandwidth that could be extracted from this very ordinary typical January La Nina mid latitude high pattern, what can weaken the Azores Ridge and add further amplification and make some of the FI extrapolations that have been/are being seen closer to reality?

Frictional Torque enhancement is indicative of rising angular momentum tendency, southward moving tendency of the jet and greater amplification flux enablement. These factors relaxing the grip of the sub tropical ridging as dictated by the upstream Pacific Nina pattern of anomalous ridges in both the NE Pacific and the Atlantic

Eastward propagation of tropical convection into the Western Pacific will forge such helpful trends closer but such an evolution is not as easy as the late autumn when the extra tropics were more co-operative and receptive to additions of westerly winds and poleward rossby wave propagation (amplification) heading eastward through the Northern Hemisphere. (This process was halted just as it was about to deliver - hence the seeming consensus for amplified cold early on).

For the reason why it might not be totally straightforward, we return to the OLR anomalies map. MJO activity has to negotiate the easterly wind anomalies present in the Pacific which would tend to snuff them out through the wind shear evident in front of the convection wave. On this basis we can look at the W&H plots and extract early caution as to how attempted eastwards propagation might progress as  we head through January.

 

 

 

As much tropospheric forcing as possible will be needed to create amplification and also agitate the wQBO assisted vortex (sounds all to familiar).  Hopes maybe rest on further retrogression of the Pacific ridge allowing the vortex position to shift NW,wards. This allowing some height rises to the NE to arrive via the back door courtesy of greater amplification arriving from upstream. Its in this sense that increased amplitude of any convective activity stemming from the Pacific is most required and welcomed.  Seasonal wavelength changes as we head deeper into the second half of winter mean that such an evolution becomes more and more important to enable eastward propagating convection (and hence the downstream amplification)

Otherwise this could well continue to be a season of mid latitude settled high pressure alternating with less settled westerlies and truncated chilly NW'erlies.

 

                             

Hi Tamara

Your post is so involved and detailed its hard for me to understand everything in detail.

But i will ask a question...

In laymens terms the very cold trough heading down to Greece as we speak was within a hairs breath of heading our way if it had not been for a reasonably localised feature being how the Azores Low eventually interacted with the jet, and despite early signs it may head east and undercut, it was eventually modelled to run west around the high and subsequently changed the entire flow for our patch.

Now if we had indeed seen that Azores low run east then the entire European pattern would have flipped with the cold coming our way. Can we put this type of localised synoptic development down to all the global factors you highlight, like the poleward rossby wave propagation, MJO, Pacific Nina pattern, The Global Wind Oscillation, Outgoing Longwave Radiation and so on......or were we just unlucky?

[mcweather]

My eyebrow is somewhat raised by tonights 12 ecm although I will be happier to see that exact development inside the 120 mark then I might raise my other eyebrow as well.

Even allowing for Tamara's cautionary tale of things unconducive  to prolonged  cold and snow . If we were able to squeeze a cold and snowy week out of this otherwise rather boring (so far at least) winter a lot of us on here would be pretty happy.

Edited January 5, 2017 by mcweather

[Nick F]

Quick look at the 12z EPS mean, as at work, but more pronounced ridge NE across the UK towards Norwegian Sea / northern Scandi days 11-12 which hasn't been evident in 11-15 day period of the EPS on recent runs - so perhaps some support for ridging in this direction to maintain post day 10.

[radiohead]

8 minutes ago, feb1991blizzard said:

The 12z EPS 240 mean not backing the op.

 

In fact its closer to the 0z op than the 12z op at T240.

I would expect quite a lot of scatter at Day 10. I'm just happy that there is  good support for the onset of this cold shot at least.

Edited January 5, 2017 by radiohead

[Guest]

20 hours ago, Nouska said:

Surely this cold an upper air mass could give a chance of polar low formation. It's originating over Greenland and following some of the favoured routes as in the papers linked by Knocker and John Holmes.

Of course, we have to get it to verify but I'm more confident than usual, having looked at the finer detail for the ECM model on the Icelandic site. Both bring this in but there are issues with timing and no doubt shortwaves once we get to five days out.

The EPS 00Z T850 mean +192 at circa -8C is nothing to be sniffed at.

Very interesting spot Nouska - let's hope that it verifies (one model and D8). We used to get polar lows much more frequently in the 1960s and 1970s when the Arctic sea ice was much more extensive and often got quite close to the northern shores of Iceland. I can remember 3 great examples giving widespread snowfall. First week in December 1967 (4 to 8 cm quite widely), 7th February 1969 which produced about 12 to 15 cm in a powder snow blizzard, in about 3 to 4 hours, right down to the south coast on a straight northerly (in a period of numerous NW to N cold snaps producing many brief snow accumulations) and March 4th 1970 on an unusually cold north-westerly with large parts of Britain getting 15 cm to 30cm. I am very busy this evening. Perhaps someone else might like to check back on the historic charts and post them up for a comparison to the ones above. I think I have the dates right (definitely for the middle event). My memory is better at recalling those historic events compared to very recent events (practically none, I know). If these features materialise they can pop up quite suddenly (perhaps with less than 72 hours notice) and even during predominantly mild Winters.

@Nouska Thank you. As if by magic, within half an hour, Nouska finds the charts for the 3 events that I outlined (see her post a few below this one).  See how all the events developed out of a milder pattern just a few days beforehand.The March 1970 event ended up with a more significant feature which eventually developed a warm (or slightly) less cold sector as it moved south eastwards. The February 1969 example was very different. The tiny feature hardly shows up on the standard pressure charts. This was shown on the hand drawn met office charts as a completely enclosed low pressure (and looked like a bullseye on a dartboard) which was no more than about  50 to 75 miles across, always remaining fully aligned with the flow, no deepening at all once it formed and it never developed a warmer sector. It is amazing how such a small feature could give such a widespread snowfall. We talk about near misses but this is the polar opposite (almost literally!) with the snow confined entirely to Britain. So, it can happen!

@Tamara Thank you for another outstanding post. I can see that you went out of your way to explain part of this complex subject so that more of us less technical people can better understand what you were saying. I, for one, am learning a lot from each of your posts and really appreciate your effort. It is such a shame that a few later posters felt the need to make some very sarcastic comments.

@Nouska and a second thank you for your link to the designated NW thread for the Jan 2015 polar low event. I just spent an hour (which I didn't really have available today!) going through it. Anyone who needs a snow fix should read through this thread and the video of the snowfall on page 21 is superb. In the "fairly unlikely" event that next week's arctic outbreak does materialise "and" is ripe for spawning polar low development, many of us on the MOD will be paying close attention. Then "if" the early signs are there, we'll need another designated thread. Extreme wishful thinking on my part I know.  Here's the link again to the Jan '15 event: 

 

Edited January 6, 2017 by Guest
To thank Nouska and Tamara

[Frosty.]

2 minutes ago, radiohead said:

I'm just happy that there is  good support for the onset of this cold shot at least.

Absolutely, the 12z runs are choc full of potential for snow in a little over a weeks time, far better than the nondescript dross this weekend, next week looks promising for a cold outbreak from the nw veering to the n..bring it on!

[radiohead]

GFS (P) hasn't updated at all on Meteociel today but here is this morning's GFS (P) showing a -6 2m temperature anomaly for us at T240. Only very limited charts for the Para on this site for our part of the world.

Edited January 5, 2017 by radiohead

[tinybill]

Just now, Frosty. said:

Absolutely, the 12z runs are choc full of potential for snow in a little over a weeks time, far better than the nondescript dross this weekend, next week looks promising for a cold outbreak from the nw veering to the n..bring it on!

if  the gfs  is  right    any  time  after jan 12     the  uk  could  come  to a stanstill   if  the  models  are  right!!!

[Summer Sun]

 

Edited January 5, 2017 by Summer Sun

[Methuselah]

Great post from Tamara (even if I can't quite get my head around it) But, I think it's true to say, that all the teleconnection-based forecasts have been cautionary?

There's a saying in scientific circles which broadly means 'all other things remaining the same'. It's just that, outwith the laboratory, that proviso is never met...So, until someone invents a completely perfect - in every way - model of the entire Earth-system, we're all at the mercy of chaos and probability?

I think that's just the way it is; and shooting messengers won't change it...

 

 

[bobbydog]

@Tamara Shut up and stop being sensible! 

Just out of interest, I'm saving the 12z  ECM charts from 240 down to zero, starting yesterday. Just to see how accurate it has been. I'll post them all when complete. Watch this space....

[lorenzo]

Clustering looking good, would take a similar ECM about face to the infamous 46 vs 5 ens members to derail. What could possibly go wrong ??!

Encouraging to see the operational model align to the much maligned EC monthly prognosis. Fingers crossed everyone gets a visit from old man winter..

[Nouska]

1 hour ago, Bring Back1962-63 said:

Perhaps someone else might like to check back on the historic charts and post them up for a comparison to the ones above. I think I have the dates right (definitely for the middle event). My memory is better at recalling those historic events compared to very recent events (practically none, I know). If these features materialise they can pop up quite suddenly (perhaps with less than 72 hours notice) and even during predominantly mild Winters.

Your memory is spot on - here's the three dates in mouse over format.

http://www.meteociel.fr/modeles/archives/archives.php?day=1&month=12&hour=0&year=1967&map=7&region=&mode=2&type=ncep

http://www.meteociel.fr/modeles/archives/archives.php?day=1&month=2&hour=0&year=1969&map=7&region=&mode=2&type=ncep

http://www.meteociel.fr/modeles/archives/archives.php?day=1&month=3&hour=0&year=1970&map=7&region=&mode=2&type=ncep

Other parameters available in dropdown menu.

Edit for @Bring Back1962-63

The thread on here about the last one.

..... and a January 2010 event study.

http://onlinelibrary.wiley.com/doi/10.1002/wea.740/full

Edited January 5, 2017 by Nouska

[BLAST FROM THE PAST]

 18z evolution in deep FI had what I think will occur.  Deep trough diving NW/SE across U.K. NW to N to NE to E'ly winds eventually.  Now I have mentioned re timing that GFS was too soon and that UKMO and ECM looked more like it timing wise.  ECM brings out a lovely run, UKMO would do the same.  I've had this timing and synoptic set up targeted for some considerable time.  Although confidence lowered due yo slug of Dec this has for me been the chance of coldest period of winter.  So confidence has remained in quite hopeful category.  

So synoptic path and timing and cold level (might enhance) looks very good to me.  I think we should increase our hope levels a notch or two

 

BFTP

[knocker]

No significant changes with the ten day anomalies this evening but one perhaps worth noting. The pattern change upstream with the rerogression of the Alaskan high pressure gets underway towards the end of the ten day period and briefly initiates some retrogression and amplification downstream thus allowing the energy/trough from the vortex via Greenland to dip SE over the UK bringing with it some wintry weather for a two or three day interlude. NOAA might not pick this up in the time frame but that is not to say NOAA should be ignored. Nothing here that hasn't been indicated over the last few runs

Keeping in mind the above still looking upstream at ridging Alaska into the arctic, and active Canadian vortex with the positively tilted trough running SW and the connection via Greenland to the negatively tilted trough to the east of the UK. With a flat upper flow across the US and a strong jet still leaving the eastern seaboard the zonality of the Atlantic still rather depends on the relative positions of the Azores ridge and the trough(s) as briefly discussed above the details of which will be sorted by the det, runs, A pretty safe bet that there will be short period of wintry weather later next week and overall the temps will trend below average.

The 10-15 period sees the completion of the pattern change upstream with an active vortex and a general low pressure area in the NE Pacific. Still a flat upper flow across the US and a strong jet leaving but there is still some life in the Azores HP and with weak positive anomalies in the eastern Atlantic still an upper flow over the UK from around the NW.with the trough to the east tending to positive tilt. Thus still looking at systems tracking SE and unsettled interludes with the south escaping the worst and temps still below average but a little higher than at the end of the ten day period.

Edited January 5, 2017 by knocker

[bluearmy]

2 minutes ago, cornish snow said:

Ian F thought's on next week would be welcome atm.Isn't there any way of getting him back?

I suspect that for professional reasons  that particular goose is cooked. bloody shame but it takes all sorts on here and we know we have some donuts

the eps extended are a bit different as they offer the potential for the ridging across the top of the sceuro low anomoly but more likely blocking closer to the uk by the time we reach the end of week 2. I expect quite a few clusters on offer but the London graph should show a lowering of temps later in general. wouldn't like to say where this is going after the northerly/north westerly .

[pyrotech]

11 minutes ago, cornish snow said:

Ian F thought's on next week would be welcome atm.Isn't there any way of getting him back?

i posted them on here for you 

I think ian reads stuff on here, but does not post, Just a hunch as the second part of his message seemed to answer my post on here.

Its a huge loss that we have lost such a respectable professional. May be some common curtesy on the model threads even if a poster says something you don't want to hear or don't agree with. There are many on here that would be severely missed as is Ian.

Here they are again

Ian Fergusson ‏@fergieweather  42 minutes ago

@Floodwarncouk models have been toying for a few runs now with broad idea of a more pronounced NW'ly to N'ly outbreak, but still early days

.cont'd... so yes, the likelihood of that has increased, albeit much too early to be deterministic on scope/outcome.

 

Edited January 5, 2017 by pyrotech

[damianslaw]

Models continue to trend towards a colder interlude with a flow from between west and north, by this time next week, thanks to a more amplified flow taking shape, with the effect of pulling down a deep trough into scandi and the jet taking a NW-SE trajectory, still not quite within the reliable timeframe, but the broad consensus at this point in time is for a colder shot from the NW over next weekend.

Interesting to note the amplification is aided by a change in the position of the aleutian/alaskan ridge this shown to retrogress a little. 

Would be good to see some wintry conditions next weekend - optimum time in my book, deep mid winter, coinciding with the weekend, we had a surprise snowfall second weekend of Jan last winter as well.. lets see, we've had not one snowflake fall since late November here.

 

[Catacol]

Tamara is right - we are stuck at the moment in a static pacific pattern. The graph below shows the progression of the MJO in terms of velocity potential - in an active phase the warmer colours starting in the Indian Ocean (left hand side of the graph) progress to the right as time passes. But we are not getting convection anomalies showing up as moving sufficiently into the Western Pacific (centre of the graph) to get the Rossby Wave amplification from this process to help drive our mid lat ridge higher. The forecast here sees no immediate change. It's a very flat looking profile.

There is some wave 2 action on the vortex forecast

But the signal for a disrupted lower vortex for mid month to my eye has faded a bit, and the projected zonal wind profile is fairly unexciting. It doesnt represent a vortex pumped up like last year, but it isnt a vortex on the edge of collapse either. Let's call it "average"...

 

End result? More of the same. Ridging of the Azores High under weak Nina conditions to continue - frost and seasonal cold waxing and waning for the foreseeable as demonstrated in the charts posted regularly by Knocker and John.... but for all the straining of my eyes I cant see a sustained cold pattern on the near horizon yet. A temporary toppler style pattern next week is possible as NWP is suggesting - and some snow may/will fall in places... but it isnt the sustained winter foundation many of us have been hoping/looking for so far this season. The pacific pattern certainly chose a damned bad time to move to a different phase and then go quiet.

I'm enjoying the frost and sunshine, but 10 days away from mid January it is high time the dice rolled in favour of UK winter and changed something. So far the winter has been as dry and blocked down here in the SW as has been the case for many years - but if the rest of winter plays out under these weak Nina conditions after such promising signs in November it will have to go down as a major disappointment.

However - lots of time remains.... and fingers continue to be crossed for change.