Model Output Discussion - 28th November

[Catacol]

Very good post - all 'types' got sucked in this time around incl. the 'Big Guns' on here

Follow the temps over on here once December starts:

http://www.climate-uk.com/

Let's see if we are "slightly colder". How much below average does it have to get before we call it "cold"?

[chionomaniac]

Paul, are those charts in extra?

They could be very useful for checking the validity of blocking scenarios.

[Paul]

Yep :

Paul, are those charts in extra?

They could be very useful for checking the validity of blocking scenarios.

Yep

http://www.netweather.tv/secure/cgi-bin/premium.pl?action=ensn;type=panel;sess=

[johnholmes]

Follow the temps over on here once December starts:

http://www.climate-uk.com/

Let's see if we are "slightly colder". How much below average does it have to get before we call it "cold"?

4C I think? look in the Guides I am sure the official Met O list is in there, I'll have a look in my own files

yep -4 to -5C below average is described as cold

[Bristawl Si]

Follow the temps over on here once December starts:

http://www.climate-uk.com/

Let's see if we are "slightly colder". How much below average does it have to get before we call it "cold"?

CH i've been around long enough to know what's normal in the UK weather wise.

What we're seeing, at the mo, for next week is normal - cold in north with chance of wintry precipitation, less cold and maybe wet in south.

For me a very typical UK December - dare i say it but a bit 70s/80s like.

[Timmytour]

People are getting so fed up with the models promising so much and then not delivering, they've taken to protesting in the nude outside Ian Ferguson's BBC office!!!!

Damn that low off Scotland, it's just refusing to move where we want it to go!

Edited November 28, 2012 by Timmytour

[IDO]

These charts may not be something too many are familiar with, but what they show is the sea level pressure mean from the ensembles as the usual contour lines and the colours show the spread, which is the difference between the highest and lowest ensemble run - ie a high spread means a large difference between highest and lowest so less certainty in terms of the outcome.

To put a baseline in, here's the chart for 24 hours and as you can see the spread is virtually all blue and therefore there's good confidence in the pressure pattern (as you'd expect)

By 96 hours, there's a bit more colour coming in there, with an increasing amount of spread surrounding developments of the low pressure system to the northwest of the UK with 5-8hpa 'uncertainty' within parts of that.

Roll it forward to 144 hours and the differences increase with the mid-atlantic, southern tip of Greenland and the east coast of the USA all areas of low confidence, and incidentally all important locations in terms of upstream development for the UK

168 hours and that increases

And by 240 hours, we're talking 10-20hpa of potential swing (on just this run alone) across much of the Atlantic, the UK and the eastern seaboard.

So, what to draw from this? 96 hours is the point to watch in terms of upstream & beyond that there's too much uncertainty to draw any real conclusions at this point. To coin an old phrase - 'more runs needed'

Not seen them before. However I would look at it another way. The synoptic pattern throughout the run looks the same. If you look where the blocks are there is high confidence that the sea level pressures (SLP) will be close to those predicted (5-8%). These higher confidence areas surround the Atlantic and hold in the pattern. I suspect that the micro changes of short waves and movement of the lows are why the Atlantic SLP has a higher degree of mean variance. It follows, predicting a meandering high is a lot easier than fast changing Atlantic travelling lows.

I would therefore accept that spread as not significant (10-20%), and would not infer that this correlates to a low confidence in the output. Its more a low confidence in the micro elements of how deep the lows become and where they will be blown. If you cannot have confidence in the GFS ensembles on this showing (upto T168): http://cdn.nwstatic.co.uk/ensimages/ens.20121128/12/t850London.png you never will.

[Paul]

Not seen them before. However I would look at it another way. The synoptic pattern throughout the run looks the same. If you look where the blocks are there is high confidence that the sea level pressures (SLP) will be close to those predicted (5-8%). These higher confidence areas surround the Atlantic and hold in the pattern. I suspect that the micro changes of short waves and movement of the lows are why the Atlantic SLP has a higher degree of mean variance. It follows, predicting a meandering high is a lot easier than fast changing Atlantic travelling lows.

I would therefore accept that spread as not significant (10-20%), and would not infer that this correlates to a low confidence in the output. Its more a low confidence in the micro elements of how deep the lows become and where they will be blown. If you cannot have confidence in the GFS ensembles on this showing (upto T168): http://cdn.nwstatic..../t850London.png you never will.

You're talking confidence at up to 168 though, but you're illustrating it with the graph for conditions in London, at that stage though the lack of certainty regaring the features which will shape the UK's weather beyond that point are still in the Atlantic, so it's essentially comparing apples and pears. One shows a fairly reasonable degree of ensemble confidence to 168 at a single point in the UK, the other is looking at the wider picture and the subtle differences at 96 hours which wound forward lead to significant differences (and therefore lower confidence) in what will eventually happen across the UK.

To illustrate the point - here's the 168 hour postage stamps, I'm sure you'd agree there's a pretty wide range of scenarios on there..

That's not to say I don't agree that the broader pattern is more certain, but it's the smaller developments which will ultimately shape what is seen on the ground in the UK.

[bluearmy]

indeed nick. conspiracy theories abound !!! missing data, blah blah blah. anyway, following on from ed's last post re the transfer back of energy from split vortex to split vortex - that concerns me in that with heights high around the pole, i feel this energy surge across to our north merely strengthens the northern arm. high risk strategy if we get the cold across us but would rather get some blocking to our north.

now its out, i quite like the ens run and spreads

[snow1975]

On 18z at T138, low is digging further south.

[Catacol]

CH i've been around long enough to know what's normal in the UK weather wise.

What we're seeing, at the mo, for next week is normal - cold in north with chance of wintry precipitation, less cold and maybe wet in south.

For me a very typical UK December - dare i say it but a bit 70s/80s like.

The weather may be appearing normal on the ground at present, but it is not. The state of the vortex is not normal; the amount of forecasted blocking is not normal; the southerly tracking jet is not normal either - at least in the "modern" era.

How is a 70s/80s December "typical"? Do you mean 1981 which was the 9th coldest December on record, or 1974 which still holds the record at CET 8.1 as the warmest December ever. That kind of statement means absolutely nothing because you have not defined what you mean as "typical" at all.

Edited November 28, 2012 by Catacol_Highlander

[Timmytour]

The Pub Run seems to be leading up into an unremarkable spell of weather. By which I mean, not remarkable for its cold like 2010 and not remarkable for its mildness like so many winters in the first few years of the century

[Thundery wintry showers]

That is one hell of a NE'erly. I suspect the E and SE would be absolutely battered by heavy snow showers due to the proximity of the low if that came off. A true harsh chart. A little bit of something for everyone with the strength of the flow too. Lovely.

That assessment of the ECMWF chart probably stems from the blues shown on the colour scale of Meteociel. I think the T+216-240 northerlies on both the ECMWF and GFS would probably produce mainly sleet and rain showers for eastern England.

Here are the 850hPa temperatures:

http://cdn.nwstatic....ecmt850.240.png

The cold snowy potential has been toned down on today's runs, but in truth, even the earlier UKMO runs probably suggested just a couple of days of generally snowy weather for the east due to erroneously sending the North Sea trough southwards too quickly. Trough activity will bring precipitation inland on Friday/Saturday according to the GFS, but with marginal 850hPa temperatures (-3 to -5C generally) we are probably looking mainly at sleet/rain at low levels with snow on hills. The UKMO/GFS have also toned down the potential for frontal snow next Monday but the ECMWF outputs would still support a fairly widespread frontal snow event.

The disagreement over Monday's weather is also consistent with Paul's comment about T+96 being the point at which the GFS ensembles start to differ considerably- the "big three" models also start to deviate at around that time.

Edited November 28, 2012 by Thundery wintry showers

[nick sussex]

now its out, i quite like the ens run and spreads

Yes not too bad and the longer ensembles don't look too shabby.

http://www.weerplaza.nl/15daagseverwachting/?type=eps_pluim&r=midden

That link allows you to compare both ECM and GFS 12hrs on the same page, click the far right option.

[johnholmes]

this link with a comment on the predicted upper air pattern and what is showing at the moment

http://forum.netweather.tv/topic/75105-model-thoughts-summaries-27th-nov-onward/#entry2420530

[SMU]

http://modeles.meteociel.fr/modeles/gfs/runs/2012112818/gfsnh-0-162.png?18

Possible crazy pub run coming with a vertical allignment of advection signalling pressure rising.

S

[cold snap]

http://modeles.meteociel.fr/modeles/gfs/runs/2012112818/gfsnh-0-162.png?18

Possible crazy pub run coming with a vertical allignment of advection signalling pressure rising.

S

Do we have a north easterly at 168?

I think we do

[chionomaniac]

Yes not too bad and the longer ensembles don't look too shabby.

http://www.weerplaza..._pluim&r=midden

That link allows you to compare both ECM and GFS 12hrs on the same page, click the far right option.

Interestingly the means of the ECM and GFS are fairly similar. A cool down, slight warm up, followed by another cool down.

[TEITS]

This is going to be fun watching the rest of the run because I sense an E,ly will develop later.

http://www.wetterzentrale.de/pics/Rtavn1681.png

These certainly aren't your typical UK synoptics!

[cold snap]

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=174&mode=0&carte=1

Gfs pub run where anything can happen

Edited November 28, 2012 by cold snap

[Nick F]

The 18z seems to be making quite a thing of that low that moves up from low latitudes and then gets sucked up by the PFJ around t+144. Rapid cyclongenesis as the low encounters the polar front, need to keep watch on this feature, as we may be on the receiving end of it. Not only that, it also creates a wave in the jet.

[cooling climate]

It looks to me as though the 18z is going to bring in a easterly

as the trough in the Atlantic disrupts on its way southeast.

I was wondering what with the ECM strat charts forcasting a 20c

warming at the 30mb level over the pole in the next few days we

could see the charts becoming a lot more block with a -AO and

NAO hopefully.

[SMU]

http://modeles.meteo...nh-0-180.png?18

GFS developing a big cold surface high over Scandi- A 'stealth' high- going un noticed in terms of blues & yellows at 500MB but its there..

Big snow event in the 192 timeline for the UK- will get it on the high res charts as well-

S

Edited November 28, 2012 by Steve Murr

[Catacol]

4C I think? look in the Guides I am sure the official Met O list is in there, I'll have a look in my own files

yep -4 to -5C below average is described as cold

That seems quite steep. A quick look at the CET records shows that the average CET for December is 4.06. Only a handful of Decembers have ever come in at 4 degrees lower than that, including 2010 of course. Does the Met therefore reserve the word "cold" only for a handful of such freezing months?

[PolarWarsaw]

Like the low's of mild- lets not exaggerate the high's of a great cold run.

It's at t192- It wont happen and the fact its on the 18z would suggest it WONT happen-

Fun to watch-but let's not get this in our heads.