Model Output Discussion 18th Nov.2013-12z onwards.

[Summer Sun]

The ECM mean is not interested one bit in a northerly

 

 

The GFS ensemble slowly builds pressure across the UK

 

[johnholmes]

Please read this again from steve......ecm ens MEAN will IMPROVE later :-)

 

not will=may, there is a difference

[Summer Sun]

Latest from Gibby on the 00z models

 

All models show a large High pressure close to SW Ireland with a light and slack NW flow affecting all areas with low level cloud cover bringing quiet and benign conditions to all areas over the next 24 hours. Through tomorrow cleaner and fresher, colder air will move SE behind a very weak cold front to reach all areas by evening with a dry and bright Saturday away from scattered showers over the North and East for a time, wintry over the hills. By Sunday the NW flow will of weakened as High pressure over the Atlantic ridges back in towards Southern Britain allowing milder and cloudier conditions to gradually topple down across the UK again from the NW through Sunday. This then persists in to the middle of next week with the likelihood of another spell of average temperatures under cloudy skies and light winds for all but the far North where freshening West winds and a little rain develops by then.

 

GFS then brings a weakening band of rain SE later next week followed by a more coherent spell of rain on a marked cold front which sweeps SE at the weekend bringing very cold and wintry Northerly winds with gales and heavy snow showers to all areas, heavy and prolonged with accumulations in the North and East. On this morning's operational cold weather is then shown to last throughout the following week with snow showers and perhaps some longer spells of snow possible before things quieten down under High pressure at the end of the run but with severe night frosts likely.

 

UKMO closes it's morning run with next Wednesday being mostly dry and rather cloudy still with a ridge from the Atlantic across the South. The North would see freshening Westerly winds later in the day with the risk of some rainfall later.

 

GEM this morning shows a cold front slipping SE midweek and bringing a change to colder and dry weather with overnight frost and fog later next week before the High flattens out and milder Westerly winds sink South over Britain followed by another push of colder Polar Maritime air at the end of the run bringing back cold and frosty weather and some wintry showers in the far North and NE.

 

NAVGEM shows pressure falling from the North later next week as Low pressure moves East to the North. The cloudy and benign conditions over the South would be maintained a while longer before a cold front would swing SE later next week to bring a spell of rain followed by colder weather with wintry showers in the North.

 

ECM today shows a sharp drop in temperature later next week as Low pressure crosses East to the North and a cold front sweeps SE across all areas. The weather would turn windy and cold with snow showers over all coastal areas, heavy and accumulative over the North and East temporarily before the emphasis shifts to clear skies and widespread penetrative frosts next weekend as High pressure topples in from the West eventually cutting off the Northerly feed.

 

The GFS Ensembles show only a very short cold snap towards next weekend before things recover to average or even a little above by the end of the run. The operational run is very isolated in it's persistence of cold beyond next weekend with many members showing rising temperatures including the Control run. Rainfall is very low with little for the next week across the South with only short spells of rain shown in Week 2 across the South while closer to average rainfall is likely towards the far North.

 

The Jet Stream today is projected to stay well to the North and NW of Britain over the next 7 days before it turns SE down across the UK later next week. It isn't long though before it is shown to move back North to a position close to Iceland very late in the run.

 

In Summary the next week is going to see a lot more of the same with a lot of quiet and benign weather under largely cloudy skies, very light winds and little in the way of rain, sunshine, frost or fog. There will be a temporary transition into a quieter and colder phase for 36-48hrs early in the weekend as a cold front clears SE leaving a short-lived legacy of scattered showers, wintry on hills in the North before the benign, milder and damper air returns on Sunday. It's not until later next week when a more active phase of weather looks like developing as High pressure gives way.

 

A cold front looks like sweeping South delivering what looks like a short but sharp drop in temperatures with snow showers and strong Northerly winds with some likely accumulation of snow over Northern and Eastern high ground. Thereafter there is a strong balance of agreement between the GFS Ensembles and other models that High pressure will move back in across the UK later from the West which in turn will remove the snow shower risk but introduce some very cold nights with severe frost before milder Atlantic winds begin to edge their way back into the UK, first to the NW and on to other areas later.

 

http://www.norton-radstockweather.co.uk/Model-Analysis%282859336%29.htm

[terrier]

Reading between the lines today it seems to me like 1 or 2 people are getting ahead of themselves these charts are not been supported so apart from a few days here and there I can't see a long lasting outbreak of any can't which is once again highlighted by gibby

[That ECM]

I love the way people are trying to call a snap or spell, when we just don't know yet. This is model watching at its best. I am loving the ride, good or bad. FWIW I think it will be a spell buts that's as much as guess as anyone's.

[Frosty.]

Reading between the lines today it seems to me like 1 or 2 people are getting ahead of themselves these charts are not been supported so apart from a few days here and there I can't see a long lasting outbreak of any can't which is once again highlighted by gibby

To be fair, the charts have in general been upgrading the cold potential as each day has passed, and now just because of the ecm 0z mean..we are getting ahead of ourselves, sorry but I'm with steve here, that guy knows his stuff and todays met office update is eagerly anticipated..MOGREPS and fergie tweets. :-) Edited November 28, 2013 by Frosty.

[snowice]

This mornings model headlines sponsored by Ear Muffs and Woolie Hats Ltd!

The big two ECM and GFS move towards agreement with a possible northerly, the GEM much lauded a few days ago hits the buffers or in model thread speak, takes too long to develop anything of interest so isn't mentioned anymore!

After the possible northerly interest grows as to whether this will be a toppler or whether it will be a toppler with bells and whistles on. For this we start the day with one of my paintjobs!

ECH1-240.gif

I know everyone knows I'm an upstream pattern bore but here is what we need to see for those wanting a bit more than a cold snap.

We know that the trend is likely to take the PV back towards Arctic Canada, the red circle is the key area upstream, the amplification there effects the low to the west of the UK in terms of where it throws its energy, more amplified upstream leads to this low more likely to disperse shortwave energy south and n/ne rather than east. As the PV pulls away from Siberia and Scandi its going to leave a space where the UK high can ridge to.

The happy face is just to lighten the mood because I suspect this saga will lead to the typical shredded nerves of coldies in here!!!

HI Nick,

do you think a shortwave could pop up and spoil the party?

 

[Ian Brown]

HI Nick,

do you think a shortwave could pop up and spoil the party?

 

There should be no party based on the output, but yes there is every chance of that.

[Summer Sun]

Hot off the press from Ian Fergusson on twitter

 

Cold expected by nxt Fri & into weekend 7th hopefully shouldn't pose any snow issues here in S (a different story N & NE/E coastal England)

 

Shouldn't last too long either: eventually, the cold shunted-off out to E as pressure rises again in from west and temperatures moderate.

 

However, even after few days of the much colder weather, any upturn in temps will be to perhaps average at most, so still a chilly story...

Edited November 28, 2013 by Summer Sun

[SomeLikeItHot]

To be fair, the charts have in general been upgrading the cold potential as each day has passed, and now just because of the ecm 0z mean..we are getting ahead of ourselves, sorry but I'm with steve here, that guy knows his stuff and todays met office update is eagerly anticipated..MOGREPS and fergie tweets. :-)

 

The ensemble mean often doesn't really tell the full story so while useful shouldn't be taken as most likely outcome unless they are clustered around the mean. You really need to look at individual members and how they are splitting. A poor ensemble mean can result from 50% great and 50% rotten split particularly if there is a spread in timing. The mean is a poor measure if there is a bi-modal split. Its like standing with one foot in a bucket of ice and another in a bucket of boiling water. You don't have warm feet despite what the average foot temperature may be.

 

Looking at last nights ECM London ensembles shows that probably 2/3 of ensemble members go for some cold shot, 1/3 don't go for any cold, of those that go for cold about half to a third keep it for at least 4 days, while the others end it more quickly. That is probably the best way of looking at the chances of something. (My estimates are rough).

Edited November 28, 2013 by SomeLikeItHot

[MR EXTREMES]

to be fair frosty we had upgrades in the last cold spell that was showing a few weeks back with some stunning charts!

 

I think the models look rather poor and other that the ecm arctic blast there really is not much more to be excited about once again I believe it when I see it I can see the whole pattern changing for the worse once again as nick sussex suggests sw drama can really ruin the situation and that the models are really not able to model a sw development in short notice!

 

although sw can also favour in building cold they can also disrupt a progressing pattern.

 

a few more days and we will know for sure im hope im wrong and that people wont be left disappointed again.

 

but the ecm screaming arctic blast is still way out in fi and other than that I don't see anything trending any futher than this cold snap.

yep and even ian f suggest this to so a brave call by the met for a short cold snap but length rather short sharp for some.

Edited November 28, 2013 by emotional rollercoaster

[terrier]

So we have heard it from Ian ferguson that the cold spell shouldn't last too long. So I would now go along with a 3/4 day toppler before we see us back to something akin to what we have now.

[SMU]

Just a comment on the ECM mean ( as I said the same thing yesterday )

 

The mean will catch up- this is a complex pattern development- The Superior resolution of the ECM operational will be able to resolve the shortwave pattern much better than the ensembles which will try to go off at different tangents-

 

Remember the GFS ensembles are All tweaked as well towards different outcomes- so out of 20 IIRC there is 4 groups, of which each group is swayed towards an outcome- it used to be on Net weather Extra what there bias was but its been a long time since I looked-

 

Perhaps Paul can remind us?

 

As a result of this you will find on the 00z & the 12z there will be SOME support from the ENS, although with the bias more than likely that half are going to distort or smooth the northerly out very quickly-

 

This is why the GFS ensembles ( the milder ones ) are the outliers today- not the operational.

 

The same can be said of the ECM, I doubt they will have bias applied, however at 168 & 196 where the action is the resolution of the shortwave pattern will be significantly weaker than the operational hence the poor mean as they are flattening out the Northerly-

 

I wanted be clear this morning- I have no issue with Gibby, in reporting his take on the weather, its great informal stuff- the only difference I see is like most - there is no forecasting, its all just what the models show-

Taking it to the next level in terms of forecasting - is taking the models & removing their bias & nuances to actually generate a forecast which will often deviate to what the model shows.

 

In this situation take the following runs.

 

00z GFS always performs the best as it has no eastward bias like the 12z -

00z & 12z ECM operationals.

 

The ECM mean will catch up by tomorrow when the amplification reaches 144....

 

S

 

PS - as for Ian F tweet- its a perfect illustration of following what the models show- but doesn't mean that's going to be correct- although I guess his hands are tied moreso than posting on here with a free canvas.

 

The decider models were all wrong for this week- when they were forecasting a return for westerly weather- I distinctly remember 2 or 3 posts from Ian plus a reply to me saying the favoured outcome would be westerly.

 

Im not saying it wont be- but don't forget the last 4 years pressure anomaly - total inverse to the norm.

we should not be discounting a longer cold spell on the whim of the models when they always predict the same no matter what............

Edited November 28, 2013 by Steve Murr

[SMU]

http://www.emc.ncep.noaa.gov/gmb/STATS/html/new_acz6.html

 

GFS currently 4th on the rankings V ECM / Canadian & UKMO - & that the best run of the GFS as well

S

[Snowman.]

CFS is currently broken 9 month hasn't updated since yesterdays 6z.

[BLAST FROM THE PAST]

V Good posts Steve, I F the day before was saying SW'ly flow and average to above average temps to return, the next day the cold tweet re a 'cold spell' perhaps, now a cold snap and return to average???.  One can only assume that was tweets showing what models showed/are showing? And that shows the fickleness of models at times.

 

BFTP

Edited November 28, 2013 by BLAST FROM THE PAST

[Bristawl Si]

From Steve's post a few mins ago:

"I wanted be clear this morning- I have no issue with Gibby, in reporting his take on the weather, its great informal stuff- the only difference I see is like most - there is no forecasting, its all just what the models show-

Taking it to the next level in terms of forecasting - is taking the models & removing their bias & nuances to actually generate a forecast which will often deviate to what the model shows."

 

I've thought that for a while but didn't want to say it.

 

Like your informative posts, Steve.

[stodge]

Morning all

 

A rare chance for me to have a look at the morning's output and offer some thoughts. Down here in lowland East London, I'm not concerned about a N'ly to be honest but I do see in the orientation of the HP a number of routes to some potentially cold or very cold conditions.

 

What I don't see however and this is expect what many on here want, is a route to snow.

 

The 00Z GFS operational output offered continuing low heights in southern Europe allowing the possibility of the HP becoming oriented in such a way as to allow a continental feed to the south or at worst almost calm conditions over the UK.

 

Make no mistake, calm clear conditions in mid December (even without snow cover) aren't going to be mild and fog-prone areas could well see ice days if inversion takes hold. For me, the question is where the HP will go after any long or short-lived N'ly incursion and whether it will trap any colder air within its circulation.

 

I should add that just as I don't see snow in this morning's output (beyond higher elevations where the outlook is much more promising), I also don't see zonality or long fetch SW'lies either.

 

My money (and very nice money it is too) would be on a shortish cold spell followed by a return to anticyclonic conditions but with greater risk of fog and frost than we have seen so far and some quite depressed daytime maxima where any fog lingers

[summer blizzard]

Shame it's a completely straight northerly, Scotland should be hammered though and the rest of us frozen.

 

[Due South]

Steve Murr, is the UK version of Big Joe B. Don't you just love him.

[Cecil Hogmanay Melchett]

Well its fascinating viewing for sure!!

I guess much of what happens depends on the depression forming off the Eastern seaboard in around a weeks time.

That i wouldn't imagine will be resovled for a good few days.

If the low is slower than progged then we could see some fantasic charts,if its faster (ala GEM),then we will se horid charts.

I wouldnt get too worked up if we see a fewe awful op runs,nor will i get too excited if we see some stellar outputs.

We'll have a much better idea by,say,sat/sun.

[SMU]

Shame it's a completely straight northerly, Scotland should be hammered though and the rest of us frozen.

 

 

Hi SB- id imagine with such a deep northerly & with 500MB temps sub -45c

http://www.wetterzentrale.de/pics/Rtavn2161.png

 

The conditions will be ripe for polar low development- or at very least a couple of decent troughs.

 

Just referring to my post above- forecasting via the way I do it will always have the odd miss, no-one will ever be spot on, however long term refining & more examples of the model nuances will only improve my accuracy, where as reporting what the models show will only be as good as that models resolution & bias at that point-

S

[beng]

Shame it's a completely straight northerly, Scotland should be hammered though and the rest of us frozen.

 

 

 

It may not end up as a straight Northerly though - if we get a short-wave developing in the flow. 

[Ali1977]

Not much comment on the latest GFS, must be a downgrade.

[Joe Levy]

Not much comment on the latest GFS, must be a downgrade.

No, we are just waiting to see what happens before we decide if it's a downgrade or not. In my mind, though it's slightly delayed, it seems a bit better as there is more energy in the Scandinavian trough but I could be wrong