Model Output Discussion - 18z - 6th December onward

[Alex95]

Is that a standing order? I mean I really don't buy that easterlies can't break down after 4 days because on Christmas day in 2009.....I am not downhearted. I am excited about next week and will actually be out enjoying it. What is interesting and pointless is the drive for perfection and then comments on anything but. I am sorry but your post might be correct for that event but that's all.

It's just that some people seem to think a slack NNE flow is now nailed on because there's strong support, whilst it actually isn't. We could go back to a raging easterly, or the Atlantic could move in by the end of next week, but it's daft to get hung up over upgrades/downgrades etc etc at +168 and beyond.

[damianslaw]

Sticking to the reliable timeframe first i.e. 144 hrs tops, all models in agreement of the trough dropping into Germany on Monday pulling in cold uppers from the NE with a rapid rise in heights over scandi. Both GFS and ECM are suggesting these heights will be very strong circa 1040MB or higher and extensive, which won't be easy to shift..

The ECM charts yesterday were exceptional for the time of year and I'm not surprised to see they are different today, I think the reasons for the difference are down to the projected shifting of the polar vortex as we reach the middle of the month. Until the models firm up on where the PV is likely to settle (expected over Siberia), they will continue to show various scenarios for mid-month onwards.. with atlantic/continental battleground the most obvious choice to choose at this range.

I would refrain from getting hung up on what the models are showing beyond the 144 hr range.. my own thoughts are we may see an atlantic breakdown of sorts from the SW but with a southerly tracking jet and propensity for the longwave trough to continue to drop anchor over the country such a breakdown will give rise to heights raises over Greenland thanks to the Polar vortex shifting to Siberia.. all this in time for the run up to christmas.

[chris55]

Absolutely - and as also repeatedly hinted at in UKMO MR trend standpoint. The wide spread in EC12z members by next weekend, after the significantly colder spell well-signalled until at least Thursday, does beg many questions as to how things will evolve by end of next working week - let alone further on by 20/21st, when (much akin to EC Monthly), the EC ensembles offer another meaningful cluster suggestive of Greenland blocking. A highly dynamic state of affairs into the medium range, for sure, and I'd not want to sit in the MR chair at Ops Centre, Exeter, trying to pen some focused sense from things (as they stand now) post next mid-week onwards.

Scandi high/Failed Atlantic push (with snowfall) then a Greeny high for Xmas, that'd be nice.

[Cloud 10]

Regarding the 500mb anomaly charts some have mentioned,a quick check on the NOAA CHART

issued on the 26th of November compared to now seems to show good guidance on the general pattern with a high around the mid-atlantic, and low pressure over/just east of the UK.

NOAA predicted..

Today's 12z gfs anomaly chart..

[Harsh Climate]

GFS 18z - The low trying to trigger an easterly is waaay further west on this run, expect a completly different run to the 12z! Me thinks better

Edited December 6, 2012 by Harsh Climate

[fergieweather]

Incidentally as an aside - latest modified NAE and UKV continues to paint interesting story re some snow into early tomorrow AM easing down from N England to Chilterns / E Anglia / SE.

[Jonan92]

GFS 18z - The low trying to trigger an easterly is waaay further west on this run, expect a completly different run to the 12z! Me thinks better

Also interesting to note that the low in eastern US is also further west and pushing more hot air to Greenland area than in the previous run

12z

1

18z

The result: GH 10mb stronger

Edited December 6, 2012 by Jonan92

[weather eater]

Not sure that is the case I am afraid. If that was the case do away with the models all together. The anomaly charts do not wax and wane because they are set over a period and are the "average" of data that is waxing and waning. They do not speak of surface conditions. Excellent resource of course.

Either I’ve not worded well or you are not reading right, the wax and waning is the model runs GFS 12z etc, not the anomaly charts

[Cloud 10]

Incidentally as an aside - latest modified NAE and UKV continues to paint interesting story re some snow into early tomorrow AM easing down from N England to Chilterns / E Anglia / SE.

The "raw" version looks similar to what you have described.

[DanDorsetUK]

Looks to me on this run the low is stalling very quickly out in the atlantic at 72 with the high to the south pushing further north and slowing its approach i have a feeling the low out in the atlantic is going to push south with the high in the north sinking further south.

[Geordiesnow]

How many shortwaves want to pop out of Greenland like!? Got to be wary of these as they can have an impact on the output, and its not usually a positive one for cold lovers!

[Cheese Rice]

Incidentally as an aside - latest modified NAE and UKV continues to paint interesting story re some snow into early tomorrow AM easing down from N England to Chilterns / E Anglia / SE.

The NAE seems rather vague in regards to precipitation potential. The NMM model is much more bullish with a marked feature pushing south, pivoting over NE Yorkshire.

Just in time for rush hour as it reaches Southern England.

I would imagine seeing quite aggravated snow depths over the North York Moors particularly, with a widespread covering across most of England.

Edited December 6, 2012 by Cheese Rice

[Catacol]

I tell you what - this GEFS ensemble control at T180 is a 1962/63 scenario with an elongated low pressure signal sat right underneath a huge belt of anomalous high pressure.

If you dont believe me here is Jan 3rd 1963 with a bit of Siberian vortex poised in the background. Hmmm

Edited December 6, 2012 by Catacol_Highlander

[ITSY]

A positive: higher heights over Greenland, block heading NW along with our SW heading SE

A (smaller) negative: the HP which sparks the block not as strong

- don't think that will matter

Edited December 6, 2012 by ITSY

[Cheshire Freeze]

The NAE seems rather vague in regards to precipitation potential. The NMM model is much more bullish with a marked feature pushing south, pivoting over NE Yorkshire.

Just in time for rush hour as it reaches Southern England.

I would imagine seeing quite aggravated snow depths over the North York Moors particularly, with a widespread covering across most of England.

Yes the NMM you've posted suggests that a good few places in England and maybe parts of east Wales could get a quick surprise covering. Marginal, but the risk is there.

[Matty M]

Hello shortwave drama! It is the 18z, but my word.

[IDO]

GFS looks like cold pushed east, uppers not as cold and snow risk east coast Monday/Tuesday now gone.

[stainesbloke]

I tell you what - this GEFS ensemble control at T180 is a 1962/63 scenario with an elongated low pressure signal sat right underneath a huge belt of anomalous high pressure.

If you dont believe me here is Jan 3rd 1963 with a bit of Siberian vortex poised in the background. Hmmm

Quite! Even in that mega winter there were some milder blips. Next week looks very interesting, especially next weekend.....keep that low from coming too far north and we should see a bitter easterly flow with some heavy snow in the south. Yah!

[Harsh Climate]

GFS looks like cold pushed east, uppers not as cold and snow risk east coast Monday/Tuesday now gone.

I'm not so sure

Our easterly is taking longer but may be better in the end. Look at how the forcing into the high is a little but further north on this run, this might mean when the easterly does try n push in it catches more of the UK than just south eastern areas..

[Ian Brown]

What's going on here - the cold uppers are going back East as a shortwave appears.

[Geordiesnow]

oh dear this isn't going well, we are losing the easterly.

Quite a bit of shortwave development on the GFS runs, I did warn yesterday we must be wary regarding shortwaves in the East Greenland sea.

Either way, its no real different to the ECM run, e.g it will be cold and sunny with shower activity in Eastern areas, the only real difference will be how far inland those showers would come inland in Eastern areas!

Either way, I hope these shortwaves don't come into play so much it risks ruining the output for cold lovers, especially now we are seeing an upgrade in upper air temps over Scandi!

[SMU]

http://modeles.meteo...nh-0-126.png?18

GFS now has the slider shortwave to the SW of the UK moving SE as opposed to South-

we should look flatter & more like the UKMO & ECM tonight

S

Just read the above posts- its like 2001 on snowatch

Edited December 6, 2012 by Steve Murr

[Catacol]

... and the ECM ensemble finished like this at 240

Run it back 4 days and that low pressure signal is going nowhere. We have a stalled atlantic, maybe undercutting, and a strong block. The battle lines look to be smack over the UK. As suggestions go this is absolutely as good as it gets. For those in the west especially there is no better medium term snow signal than this... we still need some luck but I honestly dont think I could dream up a better ensemble picture for heavy snow than this.

Sod's law it'll probably rain when the breakdown comes... but who knows... maybe not...

[IDO]

oh no, the squiggly lines are slightly different and the colours have moved a bit.... i must kill myself....

With an already slack easterly becoming slacker of course it may make a difference. Even less wintry outbreaks from eastern areas. Hopefully just a delay not a retreat.

[Harsh Climate]

Way more WAA up western side of greenland than 12z, you don't need a degree in meteorolgy to realise that is a very good thing!