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Winter Model Discussion - 12/01/13 06z Onwards

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Much has been written by the team on the opening of each successive MODEL OUTPUT DISCUSSION thread regarding the quality and applicability of posts. Rather than repeat all that as some fail to read it anyway, I'll start this new thread with a single plea:

PLEASE KEEP ON TOPIC!!!!

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GFS remains very positive from the early hours of Monday

gfs-2-48.png?0

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Certainly the potential for heavy falls of snow from Monday

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Am I the only person not surprised by the models this morning or of late for that matter, many of you are not listening to what the MO and the NOAA are telling you, and that’s the fact that we have record uncertainty about the uncertainty. There is always an uncertainty about any given operational, which is why we have an ensemble suite so as to give a guide to that uncertainty, what is happening now is that uncertainty is off the scale and that’s why the ensembles are not helping much either.

As ananalogy lets use simple rainfall in a BBC forecast, usually it goes along the lines of, a band of rain will move across the South West overnight bringing 1-2 cms of rain perhaps 3 locally. But with this degree of uncertainty the forecast would go along the lines of, there might or might not be a band of rain moving into the South West overnight, maybe earlier in the evening or perhaps tomorrow morning it will bring between 0 and 10 cms, locally more or less and it may turn to snow, alternatively it might not be the South West it could be in the North East.

My advice for what it’s worth is stick to 72hrs and forget the rest.

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The ECM does seem to have "gone off on one" later in its run judging by the ensembles.

post-2839-0-48064000-1357982672_thumb.png

Still a slight niggle with its 96-144 output though.laugh.png

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From the previous thread

quote name='Severe Siberian icy blast'

I think people are panicking a bit I can understand that but I think those that are worried about been too far west will see a nice supprise , not forgetting nearly all of us will have snow cover after Sunday nights front comes down so any marginal set up when the second front comes down will be affected by the existing snow cover .even if its just an inch it makes all the difference to dew points , wet bulb , air temp .

quote

This is a good point, the fact we now seem to be seeing two fronts moving through, the first being weaker but a little colder, should get some snow on the ground for many, and as SSIB says this could well tip the balance for those in any marginal conditions.

Some also asked about the two fronts,

First one moving down Sunday night, no warm sector

brack1.gif

Second one Monday afternoon, a little more marginal for some, but any snowcover could well help.

brack1a.gif

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Just catching up with the posts and I have to laugh at a comment in the previous thread saying the latest NAE is a damp squid for the SE. Talk about not looking at the charts properly.

The main core of precip hasn't even reached the SE at +48 and remains across the spine of England.

http://expert-images...011406_1206.gif

As the front is moving SE the 12Z NAE at +48 will illustrate my point.

Just add if the 06Z is similar to the 0Z with regards to prolonging this cold spell then thats a very good omen as I shall explain later.

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06z has shifted things further west upto +36.

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Just catching up with the posts and I have to laugh at a comment in the previous thread saying the latest NAE is a damp squid for the SE. Talk about not looking at the charts properly.

The main core of precip hasn't even reached the SE at +48 and remains across the spine of England.

http://expert-images...011406_1206.gif

As the front is moving SE the 12Z NAE at +48 will illustrate my point.

Just add if the 06Z is similar to the 0Z with regards to prolonging this cold spell then thats a very good omen as I shall explain later.

I think the band of precipitation showing up on the NAE is a very weak dying frontal system that probably won't even reach the South East. A second, much more active frontal system then follows on behind.

Edit. I think that's kind of what you were saying?

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gfs-2-60.png?6Monday evening still looks on the cards with the GFS for heavy snow.

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My advice for what it’s worth is stick to 72hrs and forget the rest.

BBC is going out to midnight tomorrow (morning forecast) so maybe T38 is now FI. With lack of strong high's to the north mapping these lows and now casting snow/disruptions must be a forecaster nightmare. Wonder if there are any verification stats for picking up a new 'trend' then droping it 12 hrs later. I hope JH is still in bed as we jump from chart to chart.

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Just a few points:

The ECM is the model that verifies best in the day 5 range. Therefore, it's version for later next week is a worry; however it is a little by itself so I am not going to draw too many conclusions.

The fact is the models all show very different scenarios, even the ones that stay cold, therefore they are all likely to be wrong and there will prob be a blend of solutions.

Any how, people should focus on the here and now with monday looking like a snowy day for much of the uk. Also The eye in the sky is correct in saying the snow has not even reached the time frame where it would have reached the south east on the nae.

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I think the band of precipitation showing up on the NAE is a very weak dying frontal system that probably won't even reach the South East. A second, much more active frontal system then follows on behind.

Edit. I think that's kind of what you were saying?

At the moment the NAE doesn't really suggest the front is weakening although despite what the models say in these situations you are far better off just following the radar on the day.

Slight shift W on the 06Z although probably slightly further W than the NAE is suggesting.

gfs-0-66.png?6

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Just catching up with the posts and I have to laugh at a comment in the previous thread saying the latest NAE is a damp squid for the SE. Talk about not looking at the charts properly.

The main core of precip hasn't even reached the SE at +48 and remains across the spine of England.

http://expert-images...011406_1206.gif

As the front is moving SE the 12Z NAE at +48 will illustrate my point.

Just add if the 06Z is similar to the 0Z with regards to prolonging this cold spell then thats a very good omen as I shall explain later.

It;s a good oman , cause that's what it did in DEC 2010 , 6z has just extended Monday further West and has brought some light snow in in advance of the front .... Can only be a good sign ...

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I think the band of precipitation showing up on the NAE is a very weak dying frontal system that probably won't even reach the South East. A second, much more active frontal system then follows on behind.

Edit. I think that's kind of what you were saying?

Yes it looks like the first front (GFS 06z) dies/stalls before it reaches the SE and the second front catches it and pushes that south/SE. Lots of snow SE/ EA/ E Mids, Lincs.

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The main difference between the GFS and ECM later in the week is the heights to the north of Scotland. It is a fairly weak extension of the Arctic high on the GFS caused by a perfect pv split (for the UK) and drives the Atlantic systems further south.The ECM doesn't build this feature and we see the result.

IMHO the 6z GFS had proven itself poor at modelling the area to the north this week as shown by its repeated insistence on driving Monday's sw to the NE. The 0z has been more consistent.

However, relying on the arctic high to ridge south is always full of danger, so I'm not overly confident on that solution.

We'll see what the 6z GFS shows, maybe it'll finally show Monday's system moving south!

Anyway, given model variability recently I'll wait for hi-res outputs to start modelling the upstream flow before climbing off the fence as to where we end up at the end of the week!

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It looks like some western areas will get a snow, rain and then back to snow event.

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Big differences between ECM and GFS/UKMO in the modelling of the jet post t+96, GFS and UKMO have an upper trough extension SE (-ve tilt) across the N Atlantic from the vortex over NE Canada - which forces the jet south into SW Europe. While in the meantime we see a ridge build to the north of the UK in response to this.

ECM taking the jet much further north. The model's op run this morning has a fair bit of support from the EPS members. Though a fair few HP solutions too at t+144:

http://www.ecmwf.int...t!2013011200!!/

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Fantastic uppers of -12C approaching and heavy snow showers into Lincs/Wash area.

gfs-0-78.png?6

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Battleground UK at T81: post-14819-0-09700200-1357984537_thumb.p

-12 uppers North Sea and +5 uppers SW of Cornwall. Pattern further west than 0z at this point.

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Little change so far still looking at around 12 hours or maybe more of snow for some eastern areas

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I've had a look at a snow depth chart and we are looking at 9cm by 21:00 in the NE on Monday, 16cm in eastern Scotland, and 11cm in the London area

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I think far from the snow petering out as it hits the south east, the snow will intensify as a circulation develops to the south east. I think you guys in the south east and east anglia will do best, with the east midlands and north east following close behind.

Other areas look more marginal or uncertain.

Of course, on the day amounts will vary as precipitation does wax and wane as can often be seen on the excellent net weather radar.

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I have learned more than I imagined possible in five days of following this particular series of threads. Whatever I have read on the theory of model outputs, individual interpretation and comparison is incredibly useful. Grateful thanks to all who take the time and trouble to post their thoughts here, and indeed to the mods, it's a brilliant education.

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I think that the snow event is quite nailed on in terms of delivering on monday as well. Am always dubious about low pressures sliding in from the south as they often don't push as far north as models suggest, this shortwave dropping through from the north west is nailed on now in my opinion.

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