Model Output Discussion 01/09/17

[ScottishSnowStorm]

5 minutes ago, Daniel* said:

No many a time they’ve ditched their own model and used a blend of x, y and z. That is what troubles me. 

It's just going to be another wait and see tomorrow then but isn't it always ?

[Daniel*]

As one would expect the GFS 18z is a bit of an outlier nonetheless not on the extreme side a few go even colder and stubbornly so. Considerable spread in the extended range some go mild. 

[Guest]

With the UKMO coming in for so much criticism and "seemingly" at odds with ECM and GFS, it is useful to compare their latest 12z fax charts to their 12z model run.

                           T+72                                                  T+96                                                  T+120                                                T+144

                              not published

                          T+72                                                   T+96                                                      T+120                                                      T+144

 

              

There are only very slight differences but I am used to viewing over 50 years of fax charts and prefer them. These have the fronts, troughs and dam lines and give me a rather better feel for the likely pattern evolution. Unfortunately, the fax charts only go up to T+120 and the T+144 is the critical chart. So I'll focus on the T+120s only. The fax chart shows the Atlantic HP ridging towards Greenland. The LP in the Norwegian Sea is heading in a south-south-easterly direction and the indications are for a northerly re-load to take shape. The T+144 does look a little different but I believe the T+168 chart that @SummerSun posted this afternoon did still show the Atlantic HP maintained in situ. Remember, the GFS and ECM at T+120 (shown below for comparison) are prior to their respective evolutions to the next Arctic re-load. Obviously we can all see how they evolve during the next few time frames. I'm wondering if part of the problem is that we are all guessing what comes next on the UKMO model run and basing it too much on their final (T+144) chart. They may be slightly different but they could well just find a slightly different route to the next northerly. So, my message is neither optimistic nor pessimistic but rather one of caution. Given that the MetO bulletins and other forecasts do seem to suggest cold weather continuing (with several milder blips), we can see on their next 2 runs if they really are on a similar or different path to the other models. I suspect that they already are pn the same hymn sheet and this will be confirmed by tomorrow evening. 

 

                     GFS 12z T+120                               ECM 12z T+120

.    

 

Edited November 27, 2017 by Guest
Correct typos

[ScottishSnowStorm]

GEFS 18z diagrams for here don't seem to be as good as the 12z ealrier

[Zakos]

The jet stream in the short range output is looking very weak for the time of year, I dont see much evidence for it to come crashing in once the cold air becomes established over Europe. Fingers crossed!

[ZK099]

This is a wait-and-see scenario. It's essentially GFS/ECM + other lowkey models Vs. UKMO. The UKMO could of course be correct and has been before. But currently the odds are in favour of very cold weather. 00z runs will be the most important for some time as to whether the GFS or ECM remain stubborn or move towards the UKMO. I wouldn't worry too much about the Fax charts atm but the 00z runs will shed a lot more light. Nervous few hours but good model watching regardless 

Edited November 27, 2017 by ZK099

[Duane S.]

Wow. Quick one from me, catching up with events and need sleep! We really are being treated at the moment, this isn't far off as good as it gets for this time of the year for us avid weather chart watchers!

One thing was niggling me though - the UKMO stance. The (proper) Easterly that never was, back in early Feb. I remember there was a model that refused to go with it whilst the others were consistently showing dreamy winte charts. I couldn't for the life of me remember which one it was though. I wouldn't have slept well if I didn't go back and check and I was consoled to find out it was the ECM that (correctly) showed the sinking high and all the others that backtracked eventually.

Doesnt necessarily mean anything, every time a new set of circumstances but generally, if the ECM is on board with a cold spell  (and is not out on its own), it is a good sign.

Obviously, until the UKMO does actually backtrack (assuming that it does), we should continue to be wary but with all the background signals as they are, it does seem rather isolated and out on a limb presently.

[Daniel*]

One saving grace the fax charts look interesting beforehand that crucial timeframe with wintry potential not from the odd flurry either. 

T72 

[❄️❄️❄️❄️❄️❄️❄️❄️❄️]

It's just typical, when the models continue to produce good adjustment on paper produce very upset with the exception of the top GFS, which has a cold may have a bias (although, on the contrary, it may be, ECM was a little warm bias?) Anyway. The trend towards the UK to be on the cold side of the plane, but I've seen more than enough to suggest that the snowfall will be minimal and in most places is also likely to see heavy rain, not anything too dark, but it seems waste me .And I am sure nolvety cold northerly winds, heavy rains will wear off quickly. IMO, we are paying the price for the Sun settled clip before attacked by warm air from middle latitudes when Svalbard and surrounding areas were colder than they are, then it's another story.

[Geordiesnow]

1 hour ago, RAIN RAIN RAIN said:

It's just typical, when the models continue to produce good adjustment on paper produce very upset with the exception of the top GFS, which has a cold may have a bias (although, on the contrary, it may be, ECM was a little warm bias?) Anyway. The trend towards the UK to be on the cold side of the plane, but I've seen more than enough to suggest that the snowfall will be minimal and in most places is also likely to see heavy rain, not anything too dark, but it seems waste me .And I am sure nolvety cold northerly winds, heavy rains will wear off quickly. IMO, we are paying the price for the Sun settled clip before attacked by warm air from middle latitudes when Svalbard and surrounding areas were colder than they are, then it's another story.

I'm always on the belief that I rather see the PV to be attacked when its strong rather than when its weak because as you are alluding too, we are really feeding on scraps in terms of cold air and as crewecold said in one of this posts, it is remarkable at how at upper heights just how how mild our side of the Northern Hemisphere is, of course with the Russian high its colder at the surface but I really can't stand the Russian high, its the biggest waste of space too me, it very rarely if hardly ever migrates westwards and all it does is send warmer air towards Western Russia so anyone hoping for a decent cold easterly with convective showers probably should forget it whilst that high is strong and persistent. The days of a big chunk of PV and low heights dropping into Western Russia/Scandinavia are so rare these days because of the persistance of the infamous Russian high!

As for the current Northerly, then yep, its remarkable how a Northerly that lasting 2-3 days and on paper looks fantastic can look so underwhelming on the snow prospects(at least according to the TV forecasts). I do think the GFS has a cold bias in terms of uppers as the UKMO is similar to the ECM but the uppers have marginally got colder even on the ECM so some eastern areas could wake up to a covering of snow on Thursday morning and reports of snow showers down eastern areas could well be reported by Wednesday afternoon. Certainly a bit more promising than when uppers were barely getting below -5 and the prospect of cold rain and a cold wind was at one stage on the cards with some ECM runs.

 

[Mucka]

Good morning (for cold lovers)

UKMO is moving toward ECM and GFS with that Atlantic low.

Hopefully it will be better again on the evening run.

EDIT

GFS 00z back to its old ways with a flatter trough and reluctant to retrogress the high, again I think this is part of this models bias and so long as ECM doesn't back it I would stick with the better defined (sharper) trough and quicker transition into a Northerly with a more amplified Atlantic pattern as a consequence.

Sometimes it is like the models look for any way out if a cold spell is looming for the UK.

 

Edited November 27, 2017 by Mucka

[Badgers01]

I am sat in departures at LAX just catching up with the drama before I fly home back to Blighty ... pls keep up the commentary surely the METO has to fall in line with the other two ..? 

[Cheshire Freeze]

We're struggling here guys

[Mucka]

GEM still wants to take the Atlantic low North, let's hope this morning is the last time we see that modelled. 

And here is UKMO 144, much improved but still a way to go this evening.

 

GFS takes its sweet time but gets there in the end. Still think the Atlantic low and not the trough failing to dig SE is the only real threat.

Just look how incredibly blocked it is upstream - crazy synoptic.

Edited November 27, 2017 by Mucka

[booferking]

GFS struggling to get heights into Greenland more low issues down the line UKMO could still go either way at 144hr along with gem backtrack sorry to say but this is far from done..

[Cheshire Freeze]

5 minutes ago, booferking said:

GFS struggling to get heights into Greenland more low issues down the line UKMO could still go either way at 144hr along with gem backtrack sorry to say but this is far from done..

GFS still finds a way...but this is going to be far from simple

[Mucka]

7 minutes ago, booferking said:

GFS struggling to get heights into Greenland more low issues down the line UKMO could still go either way at 144hr along with gem backtrack sorry to say but this is far from done..

I think so long as we keep that Atlantic low trapped long enough for the trough to dig SE then nothing can go wrong re the cold pattern. Even any shortwaves around Greenland would form on the East side of the ridge and keep us on the cold side.

Looking at it pragmatically I would rather have UKMO moving toward GFS and ECM and ignore GEM (I don't mean dismiss it, it is not far off UKMO just flatter upstream)

If ECM sticks to its guns and UKMO moves further toward it this evening I think we will be pretty much home and dry.

Edited November 27, 2017 by Mucka

[Cheshire Freeze]

5 minutes ago, Mucka said:

I think so long as we keep that Atlantic low trapped long enough for the trough to dig SE then nothing can go wrong re the cold pattern. Even any shortwaves around Greenland would form on the East side of the ridge and keep us on the cold side.

Looking at it pragmatically I would rather have UKMO moving toward GFS and ECM and ignore GEM (I don't mean dismiss it, it is not far off UKMO just flatter upstream)

If ECM sticks to its guns and UKMO moves further toward it this evening I think we will be pretty much home and dry.

Whichever model you look at this morning, GEM or GFS, the trop vortex looks FUBARed

[Mucka]

Only GFS Fi can escape blocking so easily, Houdini would be proud.

 

Edited November 27, 2017 by Mucka

[Cheshire Freeze]

1 minute ago, Mucka said:

Only GFS Fi can escape blocking so easily, Houdini would be proud.

 

Ends with a nice warm southerly to bring along the daffs

Edited November 27, 2017 by CreweCold

[Daniel*]

18 minutes ago, CreweCold said:

Ends with a nice warm southerly to bring along the daffs

A good things it’s in the naughty corner in extreme FI. Second chart looks like a Bartlett high nothing to see here the first one is evocative to December 2015, exceptionally mild. 

Good that the UKMO is more closer with GFS/EC this morning.

Unfortunately we can not entirely rule out the west based NAO and blowtorch southwesterlies evident on one of the 5 clusters of the EC in the extended range, but good thing there is little support. 

[Mucka]

GFS ensembles are a real mess unfortunately. Certainly they don't inspire confidence in any of the myriad of outcomes they come up with.

That said, they are marginally colder than yesterday's 00z set, so it is case of glass half full or half empty?

Edited November 27, 2017 by Mucka

[knocker]

Today any rain still around from yesterdays fronts will quickly clear the south and north east leaving a cold north westerly to northerly airflow over the UK which will be quite strong in the north with frequent wintry showers with snow on the norther hills. This will continue overnight and into tomorrow.but again there will be a northern and western bias with many parts of England remaining dry, albeit cold.

So by Weds 00 we have the not unfamiliar analysis of low pressure centred over the Baltic States and high ridging north into Iceland with the UK, as previously mentioned in a cold northerly with wintry showers in favored spots. Over the next 30 hours this slowly starts to change with the ridge adjusting NE across the Faeroes which veers the surface flow and concentrates snow showers along the east coast down to Norfolk and even a little inland. Needless to say temps not a long way above freezing  in many places apart from God's Little Acre.

This onshore flow continues overnight but the ridge is sinking south under pressure from energy running towards Iceland from NE North America,  Thus by Saturday midnight the onshore cold flow has been cut off as the UK comes under the influence of the ridge. Still cold with a widespread air frost Saturday morning but over the weekend the ridge continues to come under pressure and is relegated south west as temps rise to around average over the UK as the surface wind becomes more north westerly.

But by Tuesday 00 we are back in familiar territory with renewed amplification and the surface wind once more veering northerly as the colder air to the NW is directed south east initiating a another cold spell But wait, will the energy to the west be  strong enough to dissect the ridge? Tune in at 10 for the next installment.

 

 

Edited November 27, 2017 by knocker

[Ali1977]

GFS still good but a very slight backtrack to UKMO, and vise Versa. Middle ground in this set up not ideal, ECM will hopefully stick to its guns !! 

[Mucka]

Dare I say ECM looks fine so far at 96h re Atlantic low, actually pretty close to last nights GFS 18z

Edited November 27, 2017 by Mucka