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Hunt For Cold: Model Discussion - Heading Into Christmas

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If you're hunting for cold potential in the model output, this thread is for you. But if you'd like to look more widely at the models, please head over to the general model discussion thread.

This is a model related thread, so a general, frequent theme of the model output is a given, but it will not be strictly enforced:

  • Some topic drift, humorous responses etc are fine
  • Posts likely to lead the thread off on an entirely off topic tangent are not ok. For example (but not solely limited to): Posts entirely or mainly about Met Office, BBC or media forecasts with little or no model context, and posts solely asking for a weather forecast in a specific location.
  • Posts which start with something like 'I know this is off topic but ...' are not ok.
  • Posts which break the forum guidelines are not ok (eg trolling, troll-hunting, weather guilt tripping, overly defensive/aggressive, abusive, disrespectful to others)

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Last one from me for 6 weeks before I leave in the morning for Canada . Our experts we use in resort have told me that todays upper air soundings over the Russian Arctic are showing Easterlies now est

After a health scare I have had the best news ever and been given the all clear. What a year it has been weather wise.Just like to take the opportunity to wish Paul,all The moderating team a

Afternoon so 2 hours on the train should be plenty of time for a post- The last 2 weeks the projected SSW has gradually worked through the models & is now 'imminent' ~ 30hours away is when we

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1 minute ago, Spah1 said:

The MO are clearly going for the 3rd week of Jan for the fun to start. 

By the 6th Jan we should be seeing the goods. 


Unless of course the MO moves the goalpost to the 4th week by then

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It’s quite clear the HP will sink and then we will get some serious amplification around 15th jan onwards. 

I’m as impatient as all on here but 15th Jan onwards the fun starts. 

The MO are superior in this situation.

Jan week 3, polish off the sledge. 

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The ECM between day 7 and 8 somehow squeezes a small ridge to the north after avoiding a shortwave calamity .

The equivalent of a high wire act with a blind fold on!

Earlier at T120hrs hrs it teases with the jet cut back to the east , but upstream doesn’t play ball and the trigger shortwave disappears over the horizon.

At last low heights develop towards Iberia and the western Med . Can these hold on at day ten .

Edited by nick sussex
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1 hour ago, carinthian said:

Nice morning in Vancouver . A settled spell of weather for a few days before the next Pacific Low moves in later this week. First picture is looking over English Bay and entrance to Vancouver Harbour. Beyond is Bowen Island and the snow capped peaks in far distance over Upper Squamish and the Sunshine Coastal Region. Second picture was taken yesterday at my cousins home in Osoyoos, Southern Interior of BC. Still hunting for cold for you lot. The charts are very frustrating but that's one heck of a block over the British Isles and I sure the next few days will see some frost. Maybe, it will retrogress quicker than the current models show and open up for some Arctic air in the mix. Meanwhile back in Katschberg they have a 3 day snow event to look forward to from Wednesday thanks to a Arctic outbreak in Central and SE Europe. This follows on the heals of the recent snowfall in the Eastern Alps. Not much comfort to you snow lovers back in Blighty but its thanks to your high pressure block !! Lets hope your turn soon comes.




Further to the above post, latest ECM picture shows a crazy pressure profile over the Swiss Alps. They already had some very strong winds over the weekend with local blizzards and 125km/h winds. Looks like a repeat performance. Katschberg has a forecast of over 60cm of fresh snowfall from Wed-Sat ( sad I will not be there )  -15c at 2000m level.



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Now many of you will not realise the significance of this:


Those of you who have been reading my posts and those from the likes of @lorenzo@Catacol and others who comment on the key teleconnections will know that we've been banging on about about +ve EAMT (East Asian Mountain Torque) in particular. We could see this event unfolding a few weeks ago as part of the GSDM (global synoptic dynamic model), the GWO (global wind oscillation), GLAAM (global atmospheric angular momentum) and both FT (frictional torque) and MT (mountain torque) which all link in with tropical forcing, the ENSO state and the MJO. These charts are produced 2 days after the actual position - so this afternoon's chart (above) shows the position as on Dec 29th.  In my previous posts I said that EAMT was already rising strongly and that could be seen in the pressure distribution over eastern Asia (I showed the StormSurf charts, most recently yesterday).  Well, EAMT is not just rising but it's sky rocketing as can be seen by the red line in the chart and looks set to climb quite a bit higher, in fact with that 2 day chart time lag it already is.

I'll not go into the complexities but +ve EAMT events have an extraordinary influence on all levels of the lower and middle atmosphere and especially on the northern hemisphere global weather patterns and many of these assist directly or indirectly with setting up ridges and troughs and blocking patterns. Here are some of them:

1. A "major contributor" to wave breaking in the stratosphere (there are other influences too, of course) and vortex attacks by creating huge uplift and vertically propagating planetary waves from the Tibetan Plateau and particularly (as discovered more recently) the Mongolian Mountains, which can reach the upper stratosphere and even the lower mesosphere before reaching the "critical level" which is effectively "wind shear" in the troposphere as shown in this chart.


In the stratosphere the critical level has the easterlies above it which are the reversed winds and the planetary waves cannot break through it and are reflected (or even deflected) back down and they break at increasingly lower levels.  This produces one or more attacks on the spv (stratospheric polar vortex) and prolonged events can send up further planetary waves with attacks from above and below.  The last surge in EAMT occurred  during Dec 4th to 12th and peaked around Dec 9th/10th.  A few days later we saw some attacks on the SPV.                                                                                                                                                                                                                              

2. Now we have a further event which is likely to repeat the exercise and if there's any problem with the split or the downward propagation this may well deliver the final blow to the SPV in a few days.  In fact the timing is almost perfect with the split (if it happens) predicted for later this week.

3. EAMT also influences the tropospheric patterns with lateral planetary waves influencing the jet stream and downstream patterns in winter across the North Pacific and into N America. This can help the jet stream to meander and/or buckle.  This action in association with other factors can have knock on effects setting up the pattern and distribution of troughs and ridges around the hemisphere.

4. In the summer half of the year EAMT has a powerful influence on the Asian Monsoon.

5. The planetary waves also spread polewards and this is where it gets very interesting.  Some of us will have heard of and studied Judah Cohen's theories on early Asian Snow Cover extent and the greater likelihood of SSWs.  He recently admitted that it is more complicated than that and it was not a perfect correlation but nevertheless it does seem to work more often than not..  Over some years and particularly more recently, research has strongly suggested a link between North Asian blocking and the priming of the lower tropospheric layers and the surface to be receptive to a down welling SSW.  In several of my recent posts I've been showing those Asian pressure charts and the extraordinary expanse of HP over almost all central Asia northwards, Russia and Siberia.  I've been looking at the timing of these events and I'm pretty sure that it's no coincidence that a combination of +ve EAMT, extensive Asian snow cover (well above average right now as I showed yesterday) and the blocking regime are all coming together to make the patterns receptive or even highly conducive to downward propagation of the SSW to the surface. This obviously needs to be explored much more extensively and research into earlier SSWs (including near misses and failures) need to be considered. Another factor is GWD (gravity wave drag) which is mostly generated by the the east Asian mountains as well. That will be one of my 2019 projects. 

Malcolm @Blessed Weather and I have been studying these events and found that they fitted in perfectly to last February's SSW.  Here's the MT chart for back then:


Note the 3 spikes in EAMT.  The first one around Feb 1st to 5th and the SSW was triggered a week later on Feb 12th. The second one around Feb 20th-25th and we saw the full propagation down to the surface and just a few days later with the "Siberian Express" rushing westwards and producing the "Beast from the East" in the UK and progressing around the hemisphere to N America about a week or so later..  The final spike was March 5th-10th and the "Mini Beast" followed about a week or so later.

Overall, some of this is still theory but the extraordinary influences of +ve EAMT events have been studied for over 20 years. Now more of you might realise why I'm so excited about this month's two +ve EAMT events.  The models simply do not have much of these influences factored into how they churn out their nwp solutions and it's why they often need a few days to adjust to changes in the background signals.  Before long we are likely to see some much more sophisticated models being developed. The next few days of monitoring the model output will be totally absorbing and fascinating. 

Finally a Happy New Year to everyone and what a January we have in store for us!

David ?      

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check charts and correct typos
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5 minutes ago, nick sussex said:


At last low heights develop towards Iberia and the western Med . Can these hold on at day ten .

That's the best thing about the ECM tonight. In fact all the models have lowered the pressure in the Med in recent runs compared to a few days ago.

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Well the ECM at least is an improvement on its wretched morning run .

The best that can be said for it is the development of some lower heights towards the western Med . If there was more upstream amplitude we could have got some trough disruption which would have fed those holding the high further north and possibly a colder easterly flow into the UK.

However it’s evolution to even get to those lower heights to the south was so flimsy and on a knife edge that it could have gone horribly wrong with phasing of the shortwave and the upstream troughing .

The upstream patterns are all over the place with the ECM and GFS in different places.

My abiding sense is of relief that the ECM didn’t repeat its morning horror show !

Edited by nick sussex
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40 minutes ago, Devonshire said:

MODS - any chance of a 'Happy New Year' thread for those who don't want to bother appending such worthy sentiments to some proper model commentary? - x hundred members might otherwise derail this thread at a rather interesting time!?‍♀️ (Bah Humbug)

They will still do it in this thread anyway... splitters


BTW Happy new year everyone.

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29 minutes ago, BLAST FROM THE PAST said:

Reverse psychology......I hope. I’ll make a new post tomorrow.  I am anticipating that the pull back west of the HP will occur to allow the arctic blast from displaced PV, but December sniffed then failed. So I’m obviously wary but still believe some serious weather is coming....but am aware that it could pile down too Far East and U.K. miss .....again



Please don't curse it, aware of your December LRF with a wintery start and some noteworthy cold after Xmas!...couldn't have been more the opposite in all reality! ?

Slightly better ecm certainly an improvement on this morning, maybe some room for further improvement around day 8?

Edited by Froze were the Days
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30 minutes ago, Ed Stone said:

Meanwhile, back here in Blighty, the wait goes on, and on, and on, and on...???


Don't get hung up on the FI operational charts. The issue is the density of the grid each model uses, vertical layers and horizontal grid size, plus the programming.

GFS drops to a lower resolution after T+240 which makes the final five days largely useless; not that the operational run of any model should be taken with much seriousness beyond 5 days or so.

Stick with the ENS trend - which is good.

Check the CPC 300mb pressure anomaly trend its High pressure moving W / NW


Remember though that it's the anomalies here not the actual SLP - the trend is what we want!

Edited by Purga
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