Model Output Discussion 26/11/2012 18Z onwards

[Matty M]

Looking at the high res NAM model, it shows the low travelling up to greenland in a good position, quite far west and its also quite deep like on the UKMO. Small differences though, and a shame it doesn't model areas further east.

Good spot mate

[mackerel sky]

One thing is certain if the cold and snow doesnt materialise it makes a mockery of the daily express headlines from a few days ago.

Someone posted a very good link to Paul Hudson's weatherblog on the BBC which included about 20 front pages of Express headlines. They make no bones about it, even if bulls*t it doubles their circulation. They can blame the unregulated private forecasting market who supply them with those headlines, which will then be exaggerated.

[Long haul to mild]

Well, after another gripping day of model watching, we still aren't much further forward to be honest!

The UKMO holds out the hope of better snow possibilities for this weekend; certainly much better than the NNW flow shown on tonight's ECM which would help those in Northern Scotland but probably very little else! (From a selfish IMBY view, NNW'lys are about as useful as a sundial in a tunnel!)

However, past experience tells me that the ECM has probably got it right, those kind of flows are far more common than the ENE one shown by UKMO, which rarely seem to come to fruition.

Hoping that UKMO sticks to its guns but think we will gradually see it water down to the ECM version over the next couple of runs.

Great though that we are discussing all this and it's not even winter yet!

[SMU]

Hi Steve , This is something that I've been wondering in that if these lows that some models suggest could sneak through next week lose a bit of energy then could they not become a series of sliders

What will help breakaway sliders is if that trough over europe is alligned more south like UKMO- IE more resistence.

S

[chionomaniac]

If your post has been recently deleted, then it was off topic or replying to an off topic post.

[Matty M]

Let us compare Hi Res NAM 18z at T78hrs to GFS 12z @ 84hrs

Large differences in position/depth of low and synoptic situation around southern Greenland

Edited November 26, 2012 by Matty M

[cold snap]

Just browsing through some ensembles.

Here are the Icelandic slp's from the GFS 12Z today.

Worth noting that at the crucial period (3rd Dec) the operational is towards the deeper end of the ensembles and that there are only 2 others and the control that lower pressure quicker. If anything we should expect the 18Z to follow the ensembles then the short wave crossing the Atlantic may be more delayed and less deep - which should also give it a more southerly track.

After that the ensembles are as mad as a box of frogs!

Some ens there

So by this time next week we could have blizzards or we could have a heat wave

Never seen such wide scatter .next week is pot luck

[Interitus]

The latest CPC charts look unsettled and cold with troughing and positive anomalies to the north and nw.

http://www.cpc.ncep....10day/500mb.php

This snippet from their discussions is quite positive.

THE AO INDEX WHICH RECENTLY HAS

BEEN NEGATIVE IS FORECAST TO APPROACH ZERO BY DAY 7, BE NEGATIVE AT DAY 10, AND

REMAIN NEGATIVE THROUGH DAY 14.

We just need to get through days 7 to 10 with some trough disruption to the west and any snowmen might not turn into puddles!

A word of caution with their AO forecasts, they are quite good to day 7, poor by day 10 and tend to be way out by day 14

http://www.cpc.ncep....ensm.diff.shtml

[LomondSnowstorm]

Let us compare Hi Res NAM 18z at T78hrs to GFS 12z @ 84hrs

I'm glad other people have picked up on the NAM because it is very helpful. I have no idea of the verification statistics but for this purpose anyway it's at least as good if not better than the GFS because of its higher resoution, and it has been very consistent in showing a better positioned low much closer to the UKMO than to the GFS and yesterday's ECM. If that continues then we should see more movement from the GFS and ECM towards the UKMO upstream, which will help, although we need the euro trough and shortwaves downstream to play ball as well.

[Bobby]

That's the 00z GFS for some reason.

[SMU]

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

Spot the Murr run....

S

[LomondSnowstorm]

Today's FAX for Thursday 12pm on the top- Yesterday's FAX for Thursday 12pm on the bottom-

I've edited it to show the shortwave that appears on today's FAX that was not noted on yesterday's- this is a crucial part of the puzzle as it'll likely move s'wards and disrupt the east flow in scandi- as they ride over the shortwave and we in turn get a northerly-

As shown on the bottom edit- a plain and simple flow with no shortwave movement in between- allowing the colder uppers to reach quickly-

Of course if the shortwave is pulled back into the pattern at t96 on the FAX- it's very much game on re: north-easterly for this upcoming wknd- but I expect the shortwave to behave a la GFS- mainly because it's a pattern that the GFS has had engrained in it recently- and only really the UKMO has stuck against it

I do see the difference between the FAX charts today and yesterday, but since it also appears to be present in the UKMO I don't think it's conclusive evidence either way. What the next frame of the FAX looks like though will be of much more interest.

[weatherguy]

http://www.knmi.nl/e...agse/index.html

Spot the Murr run....

S

It has as equal a chance at coming off as any of the others

[PolarWarsaw]

That's not currently any major concern as things stand, but meanwhile UKMO advise us of following modifications to their raw GM into days 4-5 (accounting for 00z Fri to 00z Sun) -

"3. Modifications:

Low over eastern Europe moved further north into eastern parts of Scandinavia. The result of

these modifications over the UK is to prevent the very cold airmass reaching the E’ern side of the

UK during Saturday (sub 0C WBPT).

Showers have been added towards the E’ern side of the UK through the forecast period, with

existing ones intensified, brought further inland and turned wintry across inland parts of the east

during Saturday." (NB - their revised graphics for snow shower signal emphasise latter point)

Am I correct in thinking that dismisses any Battleground event over the weekend as the Atlantic encroaches then -

[Matty M]

That's the 00z GFS for some reason.

True!! Apologies.

Regardless NAM moved the low further west and deeper compared to its 12z anyway. Not as major difference compared to 12z GFS as 0z.

[fergieweather]

The UKMO holds out the hope of better snow possibilities for this weekend

Yes, but nothing extraordinary in what I see from their latest guidance sent from the MR desk - e.g., abstracted here (prepared by them less than an hour ago) -

"Friday 30 November 2012

· The showers mainly across E’ern/NE’ern parts of the UK with some central/southern and

western parts perhaps staying dry. Heaviest and most frequent showers probably coastal

parts of E England.

· Showers wintry over high ground, with snow down to around 300-400 M (though probably a

little lower in the N). Some sleet/hail to much lower levels."

"Saturday 1st December 2012

· Showers, mainly across E’ern parts of the UK, but perhaps also running down Irish Sea

coasts into parts of Wales and the SW.

· Showers wintry over high ground falling as snow down to 300-400 M initially, but perhaps to

low-levels in the far E/NE later. Sleet and hail likely at low-levels."

Edited November 26, 2012 by fergieweather

[Jason T]

Hope you don't mind MODS

For anyone wanting to learn or even enhance your knowledge of the Models,ETC for (Beginners like me) or even above.

http://forum.netweat...nd-meteorology/

http://weatherfaqs.org.uk/node/140

Both links have all you need, Don't be afraid to ask in the relevant threads either.

[SMU]

Heres a hint to analyizing the 18z V the 12z

empty all your windows / icons to net weather- ready to refresh the forum

Open X2 windows

http://www.meteociel...npara=0&carte=1

http://www.meteociel.fr/modeles/ukmo2.php?carte=1021&ech=6&nh=1&archive=0

keep refreshing one then you can tab back across to the old run to compare storm tracks, pressure differences etc-

those links are GFS V UKMO

S

That's not currently any major concern as things stand, but meanwhile UKMO advise us of following modifications to their raw GM into days 4-5 (accounting for 00z Fri to 00z Sun) -

"3. Modifications:

Low over eastern Europe moved further north into eastern parts of Scandinavia. The result of

these modifications over the UK is to prevent the very cold airmass reaching the E’ern side of the

UK during Saturday (sub 0C WBPT).

Showers have been added towards the E’ern side of the UK through the forecast period, with

existing ones intensified, brought further inland and turned wintry across inland parts of the east

during Saturday." (NB - their revised graphics for snow shower signal emphasise latter point)

That means the UKMO have moved towards the ECM mean ( & presume the MOGREPS mean) away from the UKMO Raw.

there was only 2/3 ECM pterbations that were identical to the UKMO at day 5- ^ hence the above commentary

S

Edited November 26, 2012 by Steve Murr

[bluearmy]

and that the faxes will be modified to our east

[ukpaul]

http://www.knmi.nl/e...agse/index.html

Spot the Murr run....

S

It's Saturday (120h) through to Monday where the ECM op diverges from its ensembles. Given that, I can't see the 120h fax showing any dramatic change in the Atllantic from the Met Office's outcome up to that point.

Edited November 26, 2012 by ukpaul

[chionomaniac]

Heres a hint to analyizing the 18z V the 12z

empty all your windows / icons to net weather- ready to refresh the forum

Open X2 windows

http://www.meteociel...npara=0&carte=1

http://www.meteociel...npara=0&carte=1

keep refreshing one then you can tab back across to the old run to compare storm tracks, pressure differences etc-

S

That means the UKMO have moved towards the ECM mean ( & presume the MOGREPS mean) away from the UKMO Raw.

there was only 2/3 ECM pterbations that were identical to the UKMO at day 5- ^ hence the above commentary

S

Why do you need two tabs Steve? On meteociel you just slide your mouse back and forth to compare runs - the T+24 on the 18Z is the same as the T+30 on the old 12Z run still present!

Edited November 26, 2012 by chionomaniac

[Gael_Force]

Heres a hint to analyizing the 18z V the 12z

empty all your windows / icons to net weather- ready to refresh the forum

Open X2 windows

http://www.meteociel...npara=0&carte=1

http://www.meteociel...&nh=1&archive=0

keep refreshing one then you can tab back across to the old run to compare storm tracks, pressure differences etc-

those links are GFS V UKMO

S

That means the UKMO have moved towards the ECM mean ( & presume the MOGREPS mean) away from the UKMO Raw.

there was only 2/3 ECM pterbations that were identical to the UKMO at day 5- ^ hence the above commentary

S

Why not just use the model compare option that Meteociel already provide?

http://www.meteociel...npara=0&carte=1

Activer live compare above the map

Edited November 26, 2012 by Gael_Force

[Cloud 10]

http://www.knmi.nl/e...agse/index.html

Spot the Murr run....

S

There's something else on that chart which i thought you might have mentioned?...

[Fortune's Fool]

The front next sunday is actually rather interesting, it would not take much to produce a snow event.

As in Sunday the 9th?

[Tom Quintavalle]

As Chiono, KW and others have mentioned I'm finding the latter stages of the ECM 12z pretty encouraging.

Lows diving S.E into Europe, high pressure situated just west of Iberia and lurking Arctic high............, sound familiar to any of you, who are avid archive browsers.

I wouldnt be at all surprised to see some future runs start to show high pressure to our S.W being sucked polewards toward that Arctic high, if some WAA develops in mid-Atlantic. If some of that residual energy near W.Greenland finally relents there could be a window of oppurtunity for that type of synoptic evolution.

This kind of evolution has been a precursor to some of our classic cold spells, now I could well be barking up the wrong tree but it could well be a case of short-term pain for long-term gain.

Certainly the Atlantic looks very subdued at the moment and if a few pieces of the synoptic jigsaw fall into place we could be on the cusp of really decent December cold spell.

Can anybody name a classic cold spell with the kind of synoptic evolution described above?

Regards,

Tom.