Model Output Discussion 18/11/2012 12Z onwards

[Frosty.]

The expected upcoming strat warming will give a major boost to the northern blocking during next month, as for the current model trends, next week will become quite a lot cooler than it is now and it still looks unsettled next week, probably the most unsettled weather towards the southeast with more possible flooding, also a risk of flooding increasing through the rest of this week towards the southeast as the initially strong winds fall light and fronts grind to a halt for many hours, so trouble ahead this week. Going back to next week, I can see high pressure ridging down from iceland towards nw scotland during next week with a more settled trend extending slowly south and east with increasing frost but southeast britain looks rather cold and wet after a mild wet start.

Edited November 20, 2012 by Frosty039

[VillagePlank]

What's more interesting, statistically more important, and factors out seasonal variation, is if we do the same exercise using the CET anomaly against the 1970-2000 mean. Here's the chart,

This is much more stronger correlation of about two orders of magnitude. Note that you can't post a negative CET anomaly after the AO goes beyond +2, and conversely, you can't post a positive anomaly once the AO is below about -3.

Remarkably, here's the line chart of AO vs CET Anomaly for the past 3 years,

So, I think, if you are doing long term forecasting, a good look at the AO forecast might be well worth the effort. If you take a closer look, the CET anomaly leads change sometimes before the AO changes. Curious. - this implies something else drives both these parameters and depending on the conditions at the time depends on how quickly each of the parameters are affected ie that the AO and the CET anomaly are correlated, it is because they are both being driven from the same source.

Edited November 20, 2012 by Boar Wrinklestorm

[latitude]

You can do either if you want, but the trend in a particular model is not the be all and end all of making a call for a particular scenario to develop. Trends on the models come and go all the time, sometimes the models will run with an idea for a while and then drop it, and this seems especially true of the GFS, perhaps because it goes out so far. However the experts when calling a trend are looking beyond a few runs on the GFS, especially as more tools are becoming available to them, a few runs on the GFS won’t bother them until such time as support comes from the other diagnostic tools. The move to a blocked spell is currently well supported if that then changes then so will the view of the more knowledgeable members. I would advise newbie’s and the less knowledgeable that they should only pay attention to those who seem to know what they are talking about and who back it up with evidence. Because that’s what I do, then apply my own logical and pragmatic thinking, I really can’t be bothered with all this jumping up and down getting my knickers in a twist over models that I know to be extremely fallible beyond 144hrs max.

Thank you very much. I was accused as a Troll by another member for asking the question.

[Methuselah]

I'm trying to come-up with a 'useful' (and hopefully also simple) mental visualization that might help newbies get to grips with what might happen should a narrow, but long, band of warm air be advected poleward to the point where it impinges on the polar vortex; as this seems to be the crux of what's going-on just now...And, being of the generally rather unimaginative persuasion, the best I can come up with is a jelly on a cone: if you put a jelly on a cone the one thing you can be sure of is that gravity will pull it down the sides of the cone; the one thing you cannot predict, however, is any precise detail...

What we are currently seeing on the model-runs, I think, is a narrow but sustained push of warm air directly into the vortex, which is quite likely to spill outwards as a result. But, I don't believe that any of the computer models can be expected to accurately predict the detailed outcome of something that hasn't even happened yet?

And, as for how the vortex will eventually 'repair' itself: it's anyone's guess...

PS: I've never heard of self-repairing jelly!

[Robbie Garrett]

A further response from the MetOffice if you are looking for a proffesional point of view, and take on the models output.

Talking about the media, and prospects of cold.

Post from earlier.

A response regarding the GFS output and ECMWF output reliability.

Thank you for your further email.

Of all the models we look at we tend to find that the GFS is the most variable and has a poor track record past day 8.

Obviously there will be times when it does pick something up, but on the whole it is more often wrong than right at that timescale.

This may be one such occasion but don't really know and tend to be influenced by the ECMWF model, which is also indicating colder, but possibly nothing quite so extreme.

Time will tell which is correct.

Big thank you to the MetOffice for this information from email.

Edited November 20, 2012 by Robbie Garrett

[nick sussex]

Much better upstream pattern on the GFS 12hrs run also pressure rises to the ne.

A good start to the evening.

[AWD]

Much better upstream pattern on the GFS 12hrs run also pressure rises to the ne.

A good start to the evening.

UKMO a lot flatter though;

http://www.meteociel.fr/modeles/ukmo2.php?nh=1&ech=120&carte=1021

[nick sussex]

UKMO a lot flatter though;

http://www.meteociel...=120&carte=1021

Its been like that for several days, the 144hrs when it comes out should be okay though and it does have a pressure rise to the ne.

[snowking]

Much better upstream pattern on the GFS 12hrs run also pressure rises to the ne.

A good start to the evening.

Yep fewer shortwaves and a much cleaner 12z so far from the GFS

Key one for me is here:

gfsnh-0-114.png

Note the low over NE Canada - on the 6z, that was two separate lows, the northernmost of which moved east into Greenland, which disrupted any potential heights around that area:

gfsnh-2012112006-0-108.png

SK

[AWD]

Its been like that for several days, the 144hrs when it comes out should be okay though and it does have a pressure rise to the ne.

Your right, it gets going eventually following the GFS in sending a ridge up towards Greenland;

http://www.meteociel.fr/modeles/ukmo2.php?carte=1021&ech=144&nh=1&archive=0

Pattern is a little further east however.

Edited November 20, 2012 by AWD

[No Balls Like Snow Balls]

Could be some really rather cold days across central England over the weekend and early next week, paticulary on Monday if the 12z GFS were to verify :-)

Some good times to come over the next few weeks one suspects :-)

[AWD]

NOGAPS has the HP closer to the UK and therefore doesn't get enough of a ridge into Greenland.

It would provide some frosty nights and cool days under the influence of HP however.

http://www.meteociel.fr/modeles/nogapse_cartes.php?&ech=162&mode=0&carte=1

Edited November 20, 2012 by AWD

[Barry12]

Could be some really rather cold days across central England over the weekend and early next week, paticulary on Monday if the 12z GFS were to verify :-)

Some good times to come over the next few weeks one suspects :-)

Highs of 4-5 for me, brrrrr.

[The Eagle]

Great synoptics. Shame about the lack of a cold pool to tap.

[ukpaul]

Look across to the USA for this GFS FI run, much of the country in the freezer for days and temperatures south of -20c moving in.

[AWD]

In the short term, rainfall seems to be the main issue, with flooding possible in some western locations. The GFS has some heavy rain over SW England early tomorrow morning;

http://cdn.nwstatic.co.uk/gfsimages/gfs.20121120/12/18/ukprec.png

As does the NAE;

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=ukuk&MODELL=nae&MODELLTYP=1&BASE=-&VAR=prec&HH=15&PRINT=1&ARCHIV=0&PANEL=0&INFO=0&WMO=

With a further band of heavy rain crossing the country Thursday night into Friday;

http://cdn.nwstatic.co.uk/gfsimages/gfs.20121120/12/51/ukprec.png

http://cdn.nwstatic.co.uk/gfsimages/gfs.20121120/12/63/ukprec.png

This band could also be accompanied by some very gusty/squally winds so some interesting weather on offering this week, certainly needs watching.

http://cdn.nwstatic.co.uk/gfsimages/gfs.20121120/12/45/ukwind.png

Edited November 20, 2012 by AWD

[EML Network]

That's the best 12z I have seen for a cold and snowy potential for some time now, the 12z has had a habit of underplaying the prospects of s decent cold spell for quite a while, being the less favorable run for a cold outbreak.

Since I've been mostly comparing the 12z runs...(mostly) ....(they mostly come out at night.....mostly ;-)...

So to see this run in particular catch onto the idea is a good sign,

If the 18z run follows it's recent trend, I'm expecting a pretty stella run from it later tonight.

For me that's been the best chart yet, loaded with potential from beginning to end ...more of that please :-)

[Methuselah]

New thread here:

Closing this one, now...