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Paul

Model output discussion - 1st December onwards

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Fresh thread as we roll into winter..

Not wanting to dredge up old news, but I just need to touch on some of the posts last night. In hindsight, I think we took the wrong decision to let that part of the discussion run last night, as to be honest some of what was said was out of line, outside the forum guidelines and off topic. 

Everyone is welcome to post in here, so long as they post about the models. Long posts, short posts, posts with charts, posts without. Experts, beginners, whoever. We need to all remember that, and even if some posts aren't of interest to some, they are to others, and that's a strength of this community. Sniping at and even taking the mick out of people just because they have a different style or outlook isn't a good look and lets be honest doesn't reflect well either on individuals, or our community as a whole. 

But anyway, on with the models. Please don't discuss the above in here now, it's time to move on and also we need to keep this forum on topcic. If you have feedback on the layout of the forums or anything else please use the feedback forum, and if you wish to discuss this further please feel free to pm me. 

Paul

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Again tentative sign's,  however sign's nonetheless of large lobe vortex being syphoned eastwards heading towards mid month. 

The ecm will most likely play consistent on its evolution. With hopefully pressure rises becoming a prominent evolution at base point of Greenland. 

Then its a matter of cross model divulge. 

ECH1-216.gif

ECM1-216.gif

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4 minutes ago, tight isobar said:

Again tentative sign's,  however sign's nonetheless of large lobe vortex being syphoned eastwards heading towards mid month. 

The ecm will most likely play consistent on its evolution. With hopefully pressure rises becoming a prominent evolution at base point of Greenland. 

Then its a matter of cross model divulge. 

ECH1-216.gif

ECM1-216.gif

Look at that Euro high though, i can't see much hope for anything in the cold category until that huge positive anomaly disappears. :(

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18 minutes ago, Greenland1080 said:

Basically, December is make or break for the winter, we need some decent wave activity or the winter will be dominated by the vortex and as such preclude any HLB from being able to form. Nothing new there what with the background drivers as they are, this is a very real possibility. But luckily! plenty of time left yet for us to head down an altogether different winter's path. Personally am still convinced we are going to see a big uptick in single wave activity from mid month onwards.

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I wonder if the Glosea model is still showing possible changes later on this month, or did Ian F say thought signs have gone...I can't remember!!

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Signs of a change now appearing days 9&10 ECM....things changing upstream and Euro high anomaly would be on borrowed time from this point...

ECH1-240.GIF?01-0

 

All aboard the train to the mid month change??

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ECM 240 hrs...what Happens nxt?

PV heading east. HP extending north 

towards Greenland....."I'm dreaming of a .........

 

image.png

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13 minutes ago, CreweCold said:

Signs of a change now appearing days 9&10 ECM....things changing upstream and Euro high anomaly would be on borrowed time from this point...

ECH1-240.GIF?01-0

I was just thinking the exact opposite cc looks very flat to me ?

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55 minutes ago, Greenland1080 said:

Think as Lancia has also said above, the last point there in his blog is key as we go into end of December and into new year.

Quote "Longer-term high latitude boundary conditions favor a negative bias to the AO including extensive Eurasian snow cover and low sea ice extent in the Barents-Kara seas.  The key will be how active the energy transfer from the troposphere to the stratosphere in late December, as early December looks quiet.  However if the energy transfer remains quiet, the polar vortex will remain strong, the AO mostly positive and mild temperatures will dominate the mid-latitudes." 

We need some more influence from the troposphere. There were a few charts showing a week, two weeks ago with promising tropospheric activity that may have impacted stratosphere but these have not made reality. 

PS. Happy with the end of the ECM though, compared to some recent runs!!

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Thats exactly why the northern hemispherical chart needs a mention. Although a flat mobile evolution is modeled on its viewing,  its possible evolutionary development as per forwarding. 

Its something advised to keep a check on via other suites in the next 2/5 days its fully open to debate (given) however COULD be a main player mid month and latter!

ECH1-216.gif

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6 minutes ago, northwestsnow said:

I was just thinking the exact opposite cc looks very flat to me ?

 

Look at the amplification upstream, particularly over Canada, that is what Crew is referring to I believe.

As previously stated we can't predict we would get a cold spell from that sort of set up but it would definitely put us in the game for blocking second half of Dec.

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For comparison to the day 10 ECM chart we have the day 10 GFS chart....

 

gfsnh-0-240.png?12

 

Similar upstream in as much as heights begin to lift away from the west of the Greenland area and across Canada. We end up with a highly amplified end of FI with much promise...

 

gfsnh-0-384.png?12

 

This gives some idea of what may have transpired had the ECM run further

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Personally I think today's charts have significantly improved mid months potential - maybe not blocking but a shift of the PV towards Siberia, leaving the potential of some height rises in the Atlantic. This may only lead to some better  PM shots, that will be ok though.

 

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I agree the Ecm 12z ends on a very positive note for coldies with a good chance of an incursion of Arctic air beyond T+240 hours. There is nothing I would like more than to see a nationwide cold snap and I hope mid December onwards will produce the change that most of us crave. :)

ecmt850.240.png

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29 minutes ago, CreweCold said:

Signs of a change now appearing days 9&10 ECM....things changing upstream and Euro high anomaly would be on borrowed time from this point...

ECH1-240.GIF?01-0

 

All aboard the train to the mid month change??

 

Cant see it happening tbh, its going to need some mighty wave activity now to get response from up top, if it happens its going to be at the very very earliest, early Jan.

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42 minutes ago, CreweCold said:

Signs of a change now appearing days 9&10 ECM....things changing upstream and Euro high anomaly would be on borrowed time from this point...

ECH1-240.GIF?01-0

Indeed the GFS & ECM seem to be fairly well matched at day 10 tonight

- although we need these positive height predictions to filter through to the earlier timeframes...

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Well the ecm shows a little promise at day 10 but we know at that range we are      Looking at a big straw clutch. Think we need to see some big wave activity to disrupt the pv think hopefully we will see a ssw around early Jan setting us up for a colder end to Jan Feb time which met office seem to be hinting at. In the nearer term it seems a lot more rain and gales to contend with on tonight's output

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18 minutes ago, johnholmes said:

for those looking for hope re cold then look away now as the NOAA anomaly hold out no hope in the 6-15 day time period!

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

John

i would suggest the signal is to muted at the moment - especially in the ENS MEAN to suggest otherwise - changes are just appearing at day 10 so thats the next landmark-

S

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8 minutes ago, johnholmes said:

for those looking for hope re cold then look away now as the NOAA anomaly hold out no hope in the 6-15 day time period!

http://www.cpc.noaa.gov/products/predictions/610day/500mb.php

That's the 6 to 10 day though isn't it, there could be a large difference if it was just a 10 day anomaly.

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Hi all!

as we are looking for cold think we should concentrate on the short term as at least the models are accurate on this.

there is a worrying amount of rainfall expected in Wales tomorrow with the wye, severn & vyrnwy already at breaking point. Bare a thought for those living near to the rivers as out of everyone they need to see the white stuff the most!!

as a beginner would love some accurate reading on the short term paterns to rainfall.

happy model watching 

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Good Evening All, the Atlantic train is in full swing and as I said last night "Four Lows and a Ridge" pretty sum up the outlook at the moment If we look out for coldies there is a glimmer of hope at T+168hrs  something a little colder in the flow from the Atlantic. but not long lasting by any means......:closedeyes:

tonia.png

toniax.png

000_dv1630957_si.jpg

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I am not surprised by the model outputs showing a polar vortex-dominated westerly airstream over the UK for the first part of December, as this would be wholly in accordance with the Net-Weather winter forecast, where significant polar vortex disruption isn't expected until during the course of January.

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The astronomical winter has officially started. Or perhaps “winter” is a better indication for today, as the weather is more akin to mid-autumn here in West-Europe. Over the past few days, a barrage of low pressure areas has moved into West-Europe, bringing lots of rain, wind and swaths of warm and humid air towards the continent. While this may seem boring at first, this type of dynamical weather does have a fascinating side, at least from a weather perspective. Here I will try to present a guide through the fascinations of the current weather, and also briefly go into the weather in the long term.

Ridge of high pressure, but far from sunny weather

After a wealth of low pressure systems crossing the UK, we are now in a period of relative calmness relatively speaking. This has all to do with a ridge located over the southwestern parts of Europe.

Note that I use different charts than usual (this time from tropicaltidbits.com).

GFS00.thumb.png.5ad1c91010f5bf8caac0a25b

GFS 12Z surface pressure (in black lines) and 500 hPa heights (in colours) initial conditions. Courtesy: Tropicaltidbits

Looking at the surface, we can see a 1034 hPa high pressure area centered over France. Low pressure activity is located to the northwest and northeast of this system.

In the upper levels, we can also see the same pattern, with a ridge (yellow colours pointing northward) located over France and troughs extending over the Atlantic and Scandinavia (blue colours pointing southward).

And yet, we are experiencing far from sunny weather in the UK. Why is that the case?

Heated battle between tropical and polar air

The main reasons that the weather is (at the least) not that sunny is that the UK is located directly at the battle zone between two air masses. This can be seen beautifully from satellite imagery:

EUMETRAIN.thumb.png.617f7c89eccc939cab02

Airmass satellite image of Europe. Courtesy: Eumetrain.

The purple colours indicate polar air (indicated by PM), whereas the greenish colours denote tropical air (indicated by the abbreviation TM).

At the border between the two competing air masses, there is a thick band of cloudiness. This band of cloudiness is indicative of the polar front, separating polar air from tropical air (denoted by the blue and red line). To the south of this band of cloudiness, tropical air is hurled into Europe to the northeast (see white arrow).

One could imagine that having two very different air masses that close together serves as a perfect breeding ground for low pressure formation. This separating line (the polar front) has been located over the UK for a couple of days, explaining why we have seen so many low pressure areas crossing the UK.

Another nice way to look at it is to check the potential wet bulb temperatures at 850 hPa (about 1500 m above sea level). That sounds rather complicated, but it is much easier if you assume it to be an indication of the air mass. Roughly speaking, higher values of theta-e indicate a more tropical air mass. See below:

ThetaE_06.thumb.png.a9c80025a8a6dd0b6346

GFS 12Z surface pressure (in black lines) and 500 hPa heights (in colours) T+6. Courtesy: Meteociel

Here again we can nicely see the separation between the tropical air over Western Europe (reddish colour/ high theta-e) flanked by two regions of polar air masses to the northwest over the Atlantic and northeast over Scandinavia (blue or purple colours/low theta-e). And finally at the borders between these two air masses we have the location of the polar front and perfect ingredients for development of low pressure areas.

More of the same to come?

Will we remain in the battle zone between polar and tropical air? Will unsettled weather continue to dominate the theme? Indications are strong that this will indeed be the case. As a first guide, we will take a look at the 8-14 day 500 hPa anomalies.

NOAA_Anoms.thumb.png.836fa6d0ab6532cfa1a

NOAA 8-14 day 500 hPa heights (in green contours) and anomalies (broken contours) Courtesy: NOAA.

The first thing that shows up is that the lines of equal height are still very close together at the 8-14 day range, often indicative of a westerly flow in our regions. Also, a negative height anomaly is present near Iceland. Often, troughing already exists at that location in winter, so a negative height anomaly indicates that troughing will be even stronger in that area. Most likely this will result in a stronger west-east flow (as the pressure difference between the north and the south is larger than average). Or, in other words, unsettled weather appears likely for the foreseeable future for the UK.

Records to be broken?

We could also take a different perspective, which sheds a new light on the weather to expect in the future. For example, by taking a look at the ensemble forecast for a certain place. In this case I take De Bilt, located in the centre of the Netherlands.

eps_temppluim_06260.thumb.png.b34f9a1a83

ECMWF ensemble for De Bilt as of 00Z 01-12. The red line indicates the operational run whereas the grey shades stand for the spread (uncertainty). Courtesy: Weerplaza.

For comparison, I have added a red line showing the average maximum temperature and the blue line roughly indicating the average minimum temperature for December.

Things do not get much more tentative to record breaking temperatures as in this graph. For instance, for the next few days and in the weekend to come, the minimum temperature forecasted in Bilt is higher than the average maximum temperature (!) for that date. Mild appears to be an understatement here.

Therefore, one could conclude that we are most likely to reside in tropical air for the time being. The lack of diurnal cycle (or in other words, the lack of difference between the day and night temperature) suggests it is going to be cloudy most of the time. Definitely not the most favourable outlook for winter weather.

Even at longer ranges (say 8-14 days, the same period as the NOAA 8-14 day charts are given), indications are for warmer than average weather to persist. Combined with the stronger westerly flow leads me to believe that a very mild, rainy period is about to start (or even continue).

Concluding note

While winter has started, a glance at the weather map would make it feel more like autumn. In fact, the temperatures resemble October rather than December. So it seems likely we are bound for another period of unsettled, very mild weather. Though winter is there, it is still far, far away. Yet, there is still much interest to be found, as is hopefully proven in this post J.  

 

 

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14 minutes ago, THE CHOSEN ONE said:

John

i would suggest the signal is to muted at the moment - especially in the ENS MEAN to suggest otherwise - changes are just appearing at day 10 so thats the next landmark-

S

Time will tell Steve, however at 10 days NOAA give two bites of the cherry so to speak, 6-10 and 8-14, neither have any signal, however slight, at least to my eyes, of any suggestion YET, of the change you mention. Six days from now who knows, so by 7 December they should, if it is going to occur, be showing something? By then assuming that to be correct then both main models should be showing something similar as well and consistently.

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