General Model Output Discussion

[Frosty.]

Look for yourself.

http://en.vedur.is/w...ntic/#type=prec

Note pretty much what I said apart from on Saturday in E Scotland as I suggested.

However I do agree with you for tomorrow and Wed. However my post was referring to the ECM which starts at +72.

Northeastern Scotland has a huge window of opportunity with the persistent NE'ly winds until the weekend and sometimes enhanced by troughs pushing south or sw although it won't get anything like the coverage it deserves. Beyond the weekend, a lot depends how far the high to the north retrogresses if we are then to get a N'ly which the gfs & ecm indicate. It looks very cold in most of the uk until well into next week but it may take a little while this week for the cold air to reach the south coast.

[Troubleatmill]

The window of opportunity for convection off the North Sea varies hugely depending on how far north you are, and I think some. For East Anglia and the southeast, OK, maybe 24-36 hours. But for NE England, the window looks like being between 48 and 72 hours- from 31 December to 2 January, and from north Yorkshire northwards, there will be some tomorrow as well. And for eastern Scotland, convection will be kicking in off the North Sea starting tomorrow and not finishing until at least Saturday, suggesting a window of 96-120 hours.

i completely agree with you though, i think north east england and eastern scotland has 3 days of convective snow to look forward too & with low temps that snow is just going to build up. The south east has a small window of opportunity, but hey i guess its better than this neck of the woods, as you know TWS - west lancs is a dreadful spot for snow, but enjoy it up there i expect you to do really well out of this

[Snowaddict]

Anyone got the SHORT ensembles yet ECM-

Steve

Mild outlier there Steve, but followed by the Control.

Stunning ensemble mean there for De Bilt..

Could well be some ice skating on the cards...

SA

[Thundery wintry showers]

Look for yourself.

http://en.vedur.is/w...ntic/#type=prec

Note pretty much what I said apart from on Saturday in E Scotland as I suggested.

However I do agree with you for tomorrow and Wed. However my post was referring to the ECM which starts at +72.

ECMWF's precipitation outputs (or at least the ones that we get to see for free) are always very generalised, much more so than those of the GFS, and often understate convective precipitation that is generated over the North Sea.

I find it very difficult to see how we could get charts like the progression of the ECMWF from T+72 to T+120 and not see three straight days of sunshine and snow showers from them in north-eastern England, regardless of what those precipitation outputs say.

[SMU]

Mild outlier there Steve, but followed by the Control.

Stunning ensemble mean there for De Bilt..

Could well be some ice skating on the cards...

SA

thanks for that TEITS but I wanted the nice debilt ones-

these are the 15 day

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

I wanted the 0-10

S

Edited December 28, 2009 by Steve Murr

[TEITS]

Indeed, 1947 was not a continuous snow fest. The reports I've seen for February 1947 suggest that there were frequent frontal snowfalls at the boundary between cold continental air and less cold air to the south during the first week, then a long dry cloudy spell in the middle associated with high pressure and south-easterly winds, and then frequent convective snowfalls in the last week as the high retreated to Greenland and winds backed north-easterly.

That is the opposite of what I read about that winter.

The 1947 cold spell was unique compared to 1963, 78/79, 81 in as much as snow fell somewhere across the country on a daily basis. The winter of 1947 was far snowier than any other winter. When you look at the archives you can see why because HP alternated between Greenland/Scandi and there was also occasions when LP systems attacked from the Atlantic. Im sure Mr D will agree with me on this.

Anyway let me clear up what im saying once and for all so we can move on. The ECM from +144 to +240 is disappointing for the simple fact that the Greenland block moves W and we're left with a cold, slack, non descript flow which would bring mainly dry conditions.

thanks for that TEITS but I wanted the nice debilt ones-

these are the 15 day

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

I wanted the 0-10

S

Sorry about that.

I know which ones you mean but I don't have the link for the short ensembles. I do have the link for the extended ensembles which will be updated around 9.30pm.

Here is the extended ECM ensembles anyway for later on.

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

Edited December 28, 2009 by THE EYE IN THE SKY

[nick sussex]

thanks for that TEITS but I wanted the nice debilt ones-

these are the 15 day

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.html

I wanted the 0-10

S

Here you go.

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

[Snowaddict]

Here you go.

http://www.knmi.nl/e...M_06260_NWT.png

I think that is the link that TETIS posted earlier?

If I'm reading it right then shorter term wise excellent, but ECMWF Op & Control both mild outliers towards the end, but with close correlation between both..

SA

[SMU]

Here you go.

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

Cheers,both control & op on the top end-

not to worry- I doubt the op was anywhere close to reality.....

eyes down for the 18z soon....

Steve

[JoeShmoe]

Here you go.

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

speechless

[Lewis]

Cheers,both control & op on the top end-

not to worry- I doubt the op was anywhere close to reality.....

eyes down for the 18z soon....

Steve

Hi steve,

This may be a kind of daft question (and if it's off topic mods, sorry, please remove it)..

When i look at the ensembles for precipitation, how accurate are these based on the model output with regards Low pressures etc, conditions at the surface and uppers.

What I'm trying to say is how reliable are they, i know the 12z is only one run, and looking at these short term ensembles http://www.knmi.nl/waarschuwingen_en_verwachtingen/ensemble_en.html it look's very dry but with the LP close by, it does not take into consideration convective potential does it?

I feel stupid now , I'm just kind of confused.

Lewis

[nick sussex]

Upstream in the USA NOAA have gone with the following models in their outlook.

HPC PROGS UPDATED MONING AND AFTN FINAL ARE BASED ON 00Z ECMWF/GFS

ENS MEANS DAYS 3-5 THU/SAT AND 00Z ECMWF/00Z ECMWF ENS MEAN DAYS

6-7 SUN/MON NATIONWIDE.

So interestingly here they prefer the ecm morning run to tonights 12hrs, i suspect this is because the morning one held better heights near Greenland, and this should be the way forward, the general guidance is for the Greenland block to remain the main driver, it is expected to retrogress further westwards but how far is open to question, later in the extended outlook they expect the eastern USA trough to edge north eastwards this would be a positive for downstream in Western Europe as this may help edge the block a little further east, preferably we want the Greenland block to stay further east this will stop the jet from heading north towards western europe and bringing low pressure in at an unfavourable angle. It's a fine balancing act here, we want the Scandi trough close enough but not too far west as this pushes things towards a western based negative NAO which comes with more hurdles in keeping the cold.

Edited December 28, 2009 by nick sussex

[Lewis]

18z rolling and a huge upgrade, a win win for all i think on this run, with the LP further south and the lower 850's across the South making it much less marginal for many areas, and still the precipitation if further North... Much better orientation of the low!

Edited December 28, 2009 by Storm Force Lewis

[nick sussex]

18z rolling and a huge upgrade, a win win for all i think on this run, with the LP further south and the lower 850's across the South making it much less marginal for many areas, and still the precipitation if further North... Much better orientation of the low!

Yes a good start to the run, also the whole pattern is slightly further east,the southwards correction continues from the gfs.

[SMU]

18z rolling and a huge upgrade, a win win for all i think on this run, with the LP further south and the lower 850's across the South making it much less marginal for many areas, and still the precipitation if further North... Much better orientation of the low!

Yes, excellent so far- which means the SE will get the colder air quicker- good for me as im off work from Weds until Mon!!!!

As for your question earlier- The PPN on the ECm is generally frontal based & not as focussed on Convective stuff- ive seen a clear East coast on the ECM ppn & heavy PPN all day in reality-

The upper air charts are very accurate-

Steve

[03jtrickey]

Don't believe this.. GFS a good 100-120 miles further south already by +36... could be some surprises in the morning

[Lewis]

Yes, excellent so far- which means the SE will get the colder air quicker- good for me as im off work from Weds until Mon!!!!

As for your question earlier- The PPN on the ECm is generally frontal based & not as focussed on Convective stuff- ive seen a clear East coast on the ECM ppn & heavy PPN all day in reality-

The upper air charts are very accurate-

Steve

It sure is, if this continues with the progression Southwards, the whole of the SE could be game on!

I noticed a couple of people posting about dew points earlier, looking at the 12z and also the 18z i don't think it will be problem due to resolution, i have been comparing my dew point and temp now to the 12z and 18z and then the NMM, even though the NMM is closer to the mark, it's still some 0.5c higher.

These charts are stunning infact, and it looks like East Anglia could see something as early as Wednesday now.

thanks for your reply regarding my earlier question Steve, I'm no longer confused

Lewis

Edited December 28, 2009 by Storm Force Lewis

[bluearmy]

Upstream in the USA NOAA have gone with the following models in their outlook.

HPC PROGS UPDATED MONING AND AFTN FINAL ARE BASED ON 00Z ECMWF/GFS

ENS MEANS DAYS 3-5 THU/SAT AND 00Z ECMWF/00Z ECMWF ENS MEAN DAYS

6-7 SUN/MON NATIONWIDE.

So interestingly here they prefer the ecm morning run to tonights 12hrs, i suspect this is because the morning one held better heights near Greenland, and this should be the way forward, the general guidance is for the Greenland block to remain the main driver, it is expected to retrogress further westwards but how far is open to question, later in the extended outlook they expect the eastern USA trough to edge north eastwards this would be a positive for downstream in Western Europe as this may help edge the block a little further east, preferably we want the Greenland block to stay further east this will stop the jet from heading north towards western europe and bringing low pressure in at an unfavourable angle. It's a fine balancing act here, we want the Scandi trough close enough but not too far west as this pushes things towards a western based negative NAO which comes with more hurdles in keeping the cold.

i have noticed that they tend not to use 12z current day but usually do the next day Nick.

i believe this is because the ecm ens mean from the 12z is rather too late for them to effectively analyse and use in their final discussion.

regarding the retrogression of the greenland ridge, the shape of the block is different to last time and i expect we will see a different long term evolution because of this.

[nick sussex]

In terms of this continued trend to bring things further south this is often the case in these synoptic set ups, the models often underestimate the block to the north, here the models have to juggle the low wanting to move ne and the high trying to push se, one has to give.

Of course given the changes so far theres still no way at this point of calling an accurate forecast, anything the media comes out with this evening best to add a margin for error as it will probably change again tomorrow.

It would be nice to see the Greenland block boxed in for longer so we want to see troughing remain over the eastern USA and Canada for as long as possible, as soon as the high is given a chance to edge west this will reduce the downward momentum on the jet, we want the jet as far south as possible before the block starts to retrogress westwards.

Edited December 28, 2009 by nick sussex

[TEITS]

With the 18Z obviously trending further S you have to wonder what will be the reality.

Absolutely fasinating stuff.

I still think some of the GFS temp predictions are rather iffy with upper temps of -7C!

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

The mild air reaches about 100 miles further South compared to the 12z.

12z:

18z:

Pretty big change 36 hours out.

[Duane S.]

Wow that is some short-term upgrade in terms of how quick the cold air covers the whole country.

I said first thing this morning that I was convinced it was being progged too far North, this is what I had been expecting from the GFS 24 hours ago. Much more like it.

We now have (relatively speaking) model agreement for the first time in a while!

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

Wow that is some short-term upgrade in terms of how quick the cold air covers the whole country.

I said first thing this morning that I was convinced it was being progged too far North, this is what I had been expecting from the GFS 24 hours ago. Much more like it.

We now have (relatively speaking) model agreement for the first time in a while!

Indeed, colder air covering the UK by +60

http://charts.netweather.tv/gfsimages/gfs.20091228/18/60/0degisotherm.png

[bluearmy]

does the precip also end up further south?? at the moment it still looks to get as far as the north midlands. will this be modified back south ??

loved rob M on N24 21:30.

[Lewis]

does the precip also end up further south?? at the moment it still looks to get as far as the north midlands. will this be modified back south ??

loved rob M on N24 21:30.

Whats good, and also weird, is that even though the low is positioned further South, the precipitation is still further North.

I think the GFS is still playing catch up, so i expect the precipitation to be much further South on the 00z at 3:30 tomorrow morning.

Lewis