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Model Output Discussion - cold spell to end Autumn


Message added by Paul

Please only post model discussion in this thread. 

For more general chat and banter, or moans and ramps loosely around the models, please head to the banter thread:
https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/

For general weather chat including about the snow/cold chances around the country, please go to the regional threads:
https://www.netweather.tv/forum/forum/142-regional-discussions/

Thank you!

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Just now, Chris.R said:

Just a question: surely the 18z at t78 is midnight Friday and t84 is 06:00 Friday, not 01:00 and 07:00 as some posters have said, we are in GMT so why add the extra hour? Am I missing something? 

Its because they are on meteociel, I'm guessing because they have strange clock winter time alterations in continental Europe.

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You know what - I havent seen 1 hopecast on here. People have put all their points of view across in a pretty good mannor- infact its been pretty good debate. The only post that sticks out a mile

Still coming slowly off a cautious fence Long term total global atmospheric angular momentum trends can tell you a lot about pattern changes due to the effects the rises and falls in global wind-

Afternoon All - A frantic few days on here with pages & pages of posts flying through in a matter of hours- I think we have 2 main discussion points at the moment-  1) The short to

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10 minutes ago, Britneyfan said:

Annoyingly bbc really are not onboard, showing complete opposite to GFS 

What ? How are they not on board very cold weekend as per all the models GFS, ECM and UKMO . Snow showers at the weekend and talking slider lows next week but unsure of rain or snow . Sitting on the fence ? Why do people make up stuff ??? 

 

The big 3 at midday Saturday .IMG_0720.thumb.PNG.5e8d038e2c3e1329785b64d6bd213263.PNGIMG_0721.thumb.PNG.577e6d39cb88d84d01d2d3ec5184a6bd.PNGIMG_0722.thumb.PNG.3df3a71518a5bda37f65a7ad53fafbe8.PNG

 

The BBC are gonna ignore that and there not on board ?

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1 minute ago, ICE COLD said:

What ? How are they not on board very cold weekend as per all the models GFS, ECM and UKMO . Snow showers at the weekend and talking slider lows next week but unsure of rain or snow . Sitting on the fence ? Why do people make up stuff ??? 

 

The big 3 at midday Saturday .IMG_0720.thumb.PNG.5e8d038e2c3e1329785b64d6bd213263.PNGIMG_0721.thumb.PNG.577e6d39cb88d84d01d2d3ec5184a6bd.PNGIMG_0722.thumb.PNG.3df3a71518a5bda37f65a7ad53fafbe8.PNG

 

The BBC are gonna ignore that and there not on board ?

They are on board for the Northerly and they are also on board for cold thereafter, they just aren't sure where the boundary will setup between mild and cold but they think that at least a decent chunk of the UK will be under cold going on the graphic.

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2 minutes ago, feb1991blizzard said:

They are on board for the Northerly and they are also on board for cold thereafter, they just aren't sure where the boundary will setup between mild and cold but they think that at least a decent chunk of the UK will be under cold going on the graphic.

Yep I saw it . It was the fact britneyfan said it was completely the opposite to GFS when it really isn't . There saying lows coming in but unsure of cold boundary like u said . ?

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2 minutes ago, ICE COLD said:

Yep I saw it . It was the fact britneyfan said it was completely the opposite to GFS when it really isn't . There saying lows coming in but unsure of cold boundary like u said . ?

If anything what Phillip Avery illustrated graphically was a lot more GFS than ECM with the low setting up to the South West but verbally he did stress it could be further North and East.

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2 hours ago, Paul_1978 said:

Where's CreweCold disappeared to? Spends ages chasing cold charts - we get some and he's nowhere to be seen.

I think Crewe stopped posting because he thought it was becoming a waste of time posting in this thread. I haven't been keeping up with the models but in brief , is the cold spell a  go?:yahoo:

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2 hours ago, Daniel* said:

Polar Low.

Looks like one, however very early for one to show up in a model. They tend to be something that suddenly turns up unforecast or 12 hours before. But may be the models may be improving, who knows.

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2 hours ago, Quicksilver1989 said:

A curiosity further afield...
image.thumb.png.fd5c96ed12d181cfbb2c328dd71ee729.png

Anyone noticed that high over the north pole? It's pretty much been a permanent feature in some way since mid November.

Very unusual

On the contrary it' very usual and explains why we have had some winter weather. It used to be much more common than in recent years.

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25 minutes ago, alexisj9 said:

Looks like one, however very early for one to show up in a model. They tend to be something that suddenly turns up unforecast or 12 hours before. But may be the models may be improving, who knows.

Polar lows will form in the here and now in a polar flow...not the result of a gfs model run

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Nice charts all round again today. Showing that consistent propensity to correct sliders south and west, often to the point everybody stays snowless But I reiterate my point from earlier, this is the best track for the first slider to take. It would set the cold in and path the way for a potentially more potent slider #2.

Seriously though, it's just not worth worrying about the details at this stage, the fluctuations in track are WAY off being nailed. Even at 24 hours to go, that's still to early to be sure experience has taught us.

Margins are often silly tight as well between dry, snow and rain. Sat in the sweet spot centre of a, say, 25 mile radius expect a good few cm. too far south and in the rain, maybe some backedge snow at best as the low exits SE.

 

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I must say it's been an interesting last few days of moddle watching lets hope we all get to c some snow at some point this week. As for our cold sbell lasting quite a wile and likes of gfs been hinting at this too in it's far outputs. It's Interesting reading the updated AO blog from Monday.  The first two weeks of December are predicted to be characterized by three strong ridges/high pressures.  The first is along the West Coast of North America contributing to downstream troughing and cold temperatures in eastern North America.  The second is across Greenland and to the south contributing to downstream troughing and cold temperatures across Europe.  The third is centered near the Urals contributing to downstream troughing and cold temperatures across East Asia with the troughing extending further east into the northern North Pacific.  It is the last ridge/high pressure centered near the Urals that I am focused on with possible longer lasting impacts on winter weather across the NH.  http://www.aer.com/science-research/climate-weather/arctic-oscillation

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PROFILE OF A SLIDER - AN INTERESTING EVENT NOT DISSIMILAR TO SOME OF THOSE MODELLED FOR NEXT WEEK

I remember many slider events in the 1960s leading to some significant snowfalls. I lived in north London at that time. Here's an example which might help some readers (and posters) understand that you do not always need that much embedded surface cold or really low uppers to achieve a decent snowfall. It was on January 9th 1968 and in the middle of a rather cold spell - not particularly memorable compared to some of the winters in that decade and certainly no 1962-63 (which contained numerous slider events - see my post on page 134 for further details of that winter). I already kept various observations and records back then and particularly the minimum and maximum temperatures. Just as with the forecast upcoming northerly, there had been a brief northerly outbreak over the preceding two to three days with some snow showers on exposed coasts and slight to moderate overnight frosts and daytime maxes around 3c to 5c over much of England. The first chart below shows the remains of the northerly to the east with a lobe of LP from Scandinavia down to southern Europe and HP over Greenland and ridging down to the mid-Atlantic HP. The HP was already coming under attack with LP south of Greenland pushing east and starting to separate the two cells. The UK had been covered in sub -8c 850s but these were receding eastwards with -4s to -6s remaining and 0s to +4s  approaching western Ireland. There were much lower 850s over central Europe and further north into Scandinavia. The overnight minimums over England ranged from -2c to -6c in rural areas - nothing exceptional. By midday (2nd chart) the Atlantic HP was sinking south with a ridge topling into France. The LP was pushing steadily eastwards (but in hindsight you can see that it was already looking like it might turn into a slider). The 0s to +4s 850s had moved across Ireland with much of England under -4s.

That evening the forecast was for rain and much milder weather to move into the west and cross the whole country overnight with a brief period of sleet or snow ahead of it. It was still dry in London when I went to bed but it had clouded over and the temperature had  risen from 0c to +3c during the evening. By midnight (3rd chart) the LP deepened slightly and slid (or even dived) south-eastwards - it was centred over Ireland. The Atlantic HP started to rebuild northwards behind it.  You can see that the signs of something brewing now by looking at the 850s. The much higher 850s (0s to +4s) were sinking away southwards and the -8s over the extreme east had not moved any further east and much of the country was still under -4s with some parts under -6s. The same was happening at the surface with the much milder wedge receding back southwards. The LP was engaging with the colder air to its east which was just cold enough (mostly around 2c at the surface) to turn much of the precipitation from rain to snow. This part is really important as it actually applies to most slider scenarios and explains why some of the posters on here get so excited. Once a slider develops and moves in a south-easterly direction you need to focus on the conditions just ahead of it and not the much milder air behind it. By midday on January 9th (4th chart ) the LP had continued its journey south-eastwards and was now centred in northern France. It was dragging in some of the cold surface air from the continent with the sub -8c 850s moving back westwards and even some sub -12s moving into the extreme north-east of Scotland - this was already matching the coldest conditions seen during the earlier northerly! So, the second benefit of a slider is that they usually drag in much colder air as they pass through (or at least whatever cold air is available).. 

Now I'm saving the best bit until the end. I woke up around 6 am and was amazed to see well over 6" of snow and a blizzard still raging. It turned out that the northern London suburbs received from 6" to 8" with a little drifting in the quite strong easterly winds just north-east of the LP. Much of the Midlands widely received around 12" of snow. Most of this snow fell in a 4 to 6 hour period and was very wet and sticky with surface temperatures around 1c to 3c. It was the first day of term and I was an excited 15 year school boy. I had a 4 mile bus journey to school and about halfway there the bus got stuck in the deep slushy snow and I walked the rest of the journey. Back in those days, they only closed schools if they were completely cut off! 

Now, I picked this particular event because there are some strong similarities to the current pattern and what is predicted for early next week on some of the recent model runs. The surface cold and the 850s will probably not be as low now as they were over Europe and Scandinavia back then but they are likely to be low enough (I remain rather sceptical about the sub -10s shown on some charts and -6s to -8s will easily be low enough in a slider scenario based on the current pattern). This was a great example of how an unexpected (certainly back in those days) snowfall can suddenly crop up. Let's now hope that one of those model run sliders materialises and the snow chasers amongst us can strike it lucky!

            Jan 8th 1968 0000                                  Jan 8th 1968 1200                           Jan 9th 1968 0000                              Jan 9th 1968 1200

 archives-1968-1-8-0-0.png     archives-1968-1-8-12-0.png    archives-1968-1-9-0-0.png    archives-1968-1-9-12-0.png

           Jan 8th 1968 0000                                  Jan 8th 1968 1200                           Jan 9th 1968 0000                              Jan 9th 1968 1200

 archives-1968-1-8-0-1.png    archives-1968-1-8-12-1.png    archives-1968-1-9-0-1.png    archives-1968-1-9-12-1.png 

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Good post^ :) 

The uppers have trended colder this tends to happen the closer we get I find always a good thing.

T+96 GFS has -11C uppers plunging as far S as Northumberland, even -10C uppers reach the S coast. I sense it will be very near the mark off a degree or two at the very most, quite an exceptional early blast. 

image.thumb.gif.760e0ce35e5ba68cdd6c92a3b2920f38.gif

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20 minutes ago, Daniel* said:

Good post^ :) 

The uppers have trended colder this tends to happen the closer we get I find always a good thing.

T+96 GFS has -11C uppers plunging as far S as Northumberland, even -10C uppers reach the S coast. I sense it will be very near the mark off a degree or two at the very most, quite an exceptional early blast. 

image.thumb.gif.760e0ce35e5ba68cdd6c92a3b2920f38.gif

I genuinely believe the GFS has a cold bias when it comes to upper air temps, especially when you see the UKMO and ECM are more or less in agreement the uppers will be around -8. Does the GFS have a higher resolution than the Euro models in this aspect? Either way, think its hard to know for sure which model is fully right when it comes to what the actual 850 temperatures are.

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00z out to +66 brings much stronger winds for Scotland and heavier precip. Could be an interesting thursday for them. The stronger winds help drive the colder 850s south a touch quicker aswell.

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4 minutes ago, MKN said:

00z out to +66 brings much stronger winds for Scotland and heavier precip. Could be an interesting thursday for them. The stronger winds help drive the colder 850s south a touch quicker aswell.

Yes i noticed ECM was first to pick up on this yesterday and now GFS has picked up the baton :)

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1 minute ago, Weather-history said:

I think he's looking at the CFS charts for winter 2018-19........:blink2::rofl:

Kevin have you seen 0z?

Looks really good for me and thee- snow showers packing into Greater manchester thur night !! (and we are getting close to +0)!!

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