Model output discussion - 1st December onwards

[Radiating Dendrite]

12 minutes ago, GUWeather said:

OR the GFS is hinting at blocking to our north with the Low off Greenland undercutting a few days later than the Euro...? Would prefer that myself, looks to me that from 9th onwards we get the cold and snow from the 12z so far...

But the 9th is far out in lala land. I would rather a quicker progression which even though not perfect delivers in the end rather than chasing the perfect synoptic that never gets into the reliable. 

[blizzard81]

Just now, Mucka said:

RE comments on UKMO undercut.

It doesn't really undercut between 120 and 140. What happens is the low rides up the high with some energy (not really enough) disrupting SE. Yes we would have another chance with the next low if it were far enough South but we really need this potential trigger low to be a little further South and produce more undercut than shown on this afternoons output thus far as this afternnons UKMO would never pull in the cold upper air needed to produce snow (pushes too far North). I will post some comparisons from GFS ensembles when they come out as some are sure to show better undercut and of course othes will show all the energy heading up the block with little disruption of energy SE.

Great post. Level headed and saying it how it is. It does not show any hints of undercut to me. As far as GFS goes, disappointing and stormy, ugh! At least it won't be too mild lol.

[TSNWK]

1 hour ago, marksiwnc said:

Liam dutton just tweeted cold and drier in new year.  #hopeforsnow

 

I was delighted when I saw this post, as it implied to me that the met were seeing colder options within their model suites... But the impression I get since is that the 12z runs have been a little disappointing.. 

 

[Smiler1709]

People need to step back and see the general trend rather than taking each run as gospel. Each run will change for good or bad but the general trend for high pressure to the North East is building. So much more interesting model viewing. 

[chionomaniac]

13 minutes ago, Mucka said:

RE comments on UKMO undercut.

It doesn't really undercut between 120 and 144. What happens is the low rides up the high with some energy (not really enough) disrupting SE (the low at 144 to the NW of the UK is actually moving NW at this point and not SE). Yes we would have another chance with the next low if it were far enough South but we really need this potential trigger low to be a little further South and produce more undercut than shown on this afternoons output thus far as this UKMO run would never pull in the cold upper air needed to produce snow (pushed away too far North). I will post some comparisons from GFS ensembles when they come out as some are sure to show better undercut and of course othes will show all the energy heading up the block with little disruption of energy SE.

So where is the low going at T+168, considering it's route north is now blocked by raised heights here? Only one route to take....and it's a classic feeler under the block situation. 

[Mucka]

GFS ensembles undercut?

Probably 3 or 4 that show genuine undercut of possible trigger low, 3 of which I have posted below to show how the low in pushing SE under the block (into SW England)  and not N/NW up  away from the block as with UKMO.  (actually p20 last in chart doesn't quite push through)

 

 

The majority go for a UKMO type solution with the low riding up the block with varying degrees of split energy/disruption SE - some better than UKMO, some worse.

A few at the opposite end of the scale of the undercutting lows drive all the energy up and over the block.

Based on current output it looks as though the further NE you are the better chance you will have of having enough cold air in place to produce some snow.

Unfortunately it looks as any colder.drier weather will be temporary as the Atlantic gains the upper-hand again but not a done deal. Further into FI all options are pretty much open as conditions may have improved for better amplification again by then.

MetO 30 day forecasts still very disappointing for cold weather fans though.

Edited December 27, 2015 by Mucka

[chrisbell-nottheweatherman]

49 minutes ago, IDO said:

Yes too much Atlantic energy on the GFS, so little disruption and the LP system warms out the uppers, and shifts the pattern east rather than undercutting:

Fine lines, though GFS is known to en-power the Atlantic!

 

At that range, according to Ian Fergusson, the Met Office don't take GFS literally (see the following post):

https://forum.netweather.tv/topic/84555-model-output-discussion-1st-december-onwards/?do=findComment&comment=3308322

[Mucka]

15 minutes ago, chionomaniac said:

So where is the low going at T+168, considering it's route north is now blocked by raised heights here? Only one route to take....and it's a classic feeler under the block situation. 

Hey Chino, that is the question and why I said there could be other opportunities from following lows dependent on the orientation of the  block by then and track of the low, problem is the cold upper air by now is further NE and much harder to drag in and the block is weaker so disruption is likely to be less and keep those cold uppers too far N and NE. It is touch and go though and small changes int he distribution of energy at point of contact with the block can make all the difference for us.

My post that you replied to was really concentrating on the first low and the idea it was undercutting the block rather than disrupting N/NE and SE with the majority of energy heading the wrong way.

 

Edited December 27, 2015 by Mucka

[Liam J]

Was hoping to see some stellar GEFS members bringing deep cold into the UK but similar to the OP & control most direct the real cold NW in the direction of Norway. 4 maybe 5 members show a decent Scandi block setting up but the majority show an Atlantic influence of sorts in our vicinity....

Some mean 850 charts, Be very frustrating if we have a 'so near yet so far' scenario with the deep cold out of reach but I suppose the closer it is the easier it will be tap into it, right?

 

Edited December 27, 2015 by *Sub*Zero*

[IDO]

1 minute ago, blizzard81 said:

Great post. Level headed and saying it how it is. It does not show any hints of undercut to me. As far as GFS goes, disappointing and stormy, ugh! At least it won't be too mild lol.

Yes GFS and GEM have the initial trigger low not reading the script and triggering nothing. The second or third attempt are later and by then the block is too far away to expect an easterly. The undercut is then just diving under lower heights and  the pattern means no long fetch easterly, just the sinking of the jet and a pattern change to a colder upper flow. The GFS has too much energy from the vortex lobe and any potential for snow in FI is limited as the upper flow is warmed out (all possibly subject to change). However there is potential and with small changes and more trough disruption it could bring a more wintry set up. The mean T850s from D8 to D15 (at least) show the UK continuously under 0c and that hasn't happened for a while. Though no snowfest it puts us in a better position when the PV goes bust after mid Jan?

 

 

[blizzard81]

13 minutes ago, chionomaniac said:

So where is the low going at T+168, considering it's route north is now blocked by raised heights here? Only one route to take....and it's a classic feeler under the block situation. 

I feel a little rude here as I am nowhere near your level of knowledge on these matters but how can come the GFS did not undercut? How do you know that the UKMO will not go the same way as the GFS which is very similar at that timeframe.

[chionomaniac]

1 minute ago, Mucka said:

Hey Chino, that is the question and why I said there could be other opportunities from following lows dependent on the orientation of the  block by then, problem is the cold upper air by now is further NE and much harder to drag in and the block is weaker so disruption is likely to be less and keep those cold uppers too far N and NE. It is touch and go though and small changes int he distribution of energy at point of contact with the block can make all the difference for us.

My post you allude to was really concentrating on the first low and the idea it was undercutting the block rather than disrupting N/NE and SE with the majority of energy heading the wrong way.

 

I have not looked at 850's so have not even looked at where the cold is headed. You have brilliantly shown in your following post of the GFS ensembles, classic non undercutting scenarios where the orientation is all wrong and the stronger jet will ride over the top, but the UKMO is a classic undercut scenario, so I don't know why you are tying to suggest otherwise. Whether or not it verifies or leads to cold is another matter, but as undercutting highs go this looks good. At the beginning of an undercut the split negatively tilted trough often loses energy and becomes absorbed by the block and it may take a few bites of the cherry or else the block may become unfavourable tilted of drift east in time.

[SMU]

We dont actually need that atlantic low at 144 for a big undercut -

if anything if its a tad further west it will allow more ridging in the gap !!

best GFS ens

s

[MR EXTREMES]

8 minutes ago, Mucka said:

GFS ensembles undercut?

Probably 3 or 4 that show genuine undercut of possible trigger low, 3 of which I have posted below to show how the low in pushing SE under the block (into SW England)  and not N/NW up  away from the block as with UKMO. 

 

 

The majority go for a UKMO type solution with the low riding up the block with varying degrees of split energy/disruption SE - some better than UKMO, some worse.

A few at the opposite end of the scale of the undercutting lows drive all the energy up and over the block.

Based on current output it looks as though the further NE you are the better chance you will have of having enough cold air in place to produce some snow.

Unfortunately it looks as any colder.drier weather will be temporary as the Atlantic gains the upper-hand again but not a done deal. Further into FI all options are pretty much open as conditions may have improved for better amplification again by then.

MetO 30 day forecasts still very disappointing for cold weather fans though.

done deal atlantic gains upper hand I bet a bottom dollar it wont make inroads easy against the scandi block would not surprise me to see retrogression towards Greenland as vortex gets displaced into the north atlantic.

best chance of an undercut for some years.

I'm sure the ecm will throw a spanner into the works theres certainly lowering of heights into Europe as it stands the north sea is the boundary between cold from the east and certain turning cooler in the west of the uk and more so nw squeeze from both sides so to start with very mild but turning steadly cooler perhaps colder.

all this gaining pace but id still suggest still need this with in the 96hrs I reckon second bite of the cherry needed.

so we need the sausage scandi heights a lower heights to our south of coarse this could retrogress heights towards Greenland vortex getting its ass kicked more wave activity plz and mjo into phase 7 id prefer phase 8 as I believe that supports a Greenland block.

but beggers cant be choosers

[Cheshire Freeze]

At work so short on time but I agree with Chiono and Mr Murr, the UKMO 144 is an undercut and potentially very good going forward. Remember you're never going to get 100% disruption with all energy under the block. I suspect given the se'ly backed winds and preclusion of tm air mass the 144 chart precipitation is snow.

[nick sussex]

The UKMO is frustrating as we don't see the 850's, roughly at T144hrs  it looks like around -1 into the far se. Looking further east around -4 in western areas of Germany and around -7 towards the east.

In terms of frontal snow  you don't need the deep cold pool to the east, even if that doesn't reach the UK its about the temps dew points over central Europe.

 

[Mucka]

10 minutes ago, chionomaniac said:

I have not looked at 850's so have not even looked at where the cold is headed. You have brilliantly shown in your following post of the GFS ensembles, classic non undercutting scenarios where the orientation is all wrong and the stronger jet will ride over the top, but the UKMO is a classic undercut scenario, so I don't know why you are tying to suggest otherwise. Whether or not it verifies or leads to cold is another matter, but as undercutting highs go this looks good. At the beginning of an undercut the split negatively tilted trough often loses energy and becomes absorbed by the block and it may take a few bites of the cherry or else the block may become unfavourable tilted of drift east in time.

 

That is a strange post. I respect you Chino but absolutely disagree with what you are saying here.

Are we talking about the 120/144 low and not possibilities for the next low?

If you were right and I wrong then within the ensembles that show what you are describing as undecut (look like UKMO) would go on to show a stronger better oriented block than the ones I describe as undercutting (actually going UNDER the block into Europe and not riding up it toward the pole)

without even looking I can guarantee on the whole that those that have more energy heading SE UNDER the block will have a better oriented.stronger block and cold uppers closer or over the UK than those that send most energy N a la UKMO by 168 and out to end of hi res.

I can only imagine there is some misunderstanding because what I am describing is a a basic reality.

 

I haven't seen the 850's either but I don't need to understand the dynamic at play. 

Edited December 27, 2015 by Mucka

[phil nw.]

A promising UKMO run this evening.Trough disruption heading towards Europe with +ve heights extending west towards Iceland from the Scandinavian high.The low to the north of the Azores looks to be heading underneath the block.

GFS -not this time

GFS at t144 seeing too much ridging from the AH pushing north at that point.Small difference like these will tip the pattern one way or the other.

 

[inghams85]

33 minutes ago, Mucka said:

GFS ensembles undercut?

Probably 3 or 4 that show genuine undercut of possible trigger low, 3 of which I have posted below to show how the low in pushing SE under the block (into SW England)  and not N/NW up  away from the block as with UKMO.  (actually p20 last in chart doesn't quite push through)

 

 

The majority go for a UKMO type solution with the low riding up the block with varying degrees of split energy/disruption SE - some better than UKMO, some worse.

A few at the opposite end of the scale of the undercutting lows drive all the energy up and over the block.

Based on current output it looks as though the further NE you are the better chance you will have of having enough cold air in place to produce some snow.

Unfortunately it looks as any colder.drier weather will be temporary as the Atlantic gains the upper-hand again but not a done deal. Further into FI all options are pretty much open as conditions may have improved for better amplification again by then.

MetO 30 day forecasts still very disappointing for cold weather fans though.

Just to add to Chiono's post.......

You have just posted some ensembles as evidence of what an undercut looks like and try aren't undercuts AT ALL!

The UKMO almost couldn't be more classical undercut if it tried!

 

Edited December 27, 2015 by Polar Maritime
To move discussion on..

[Liam J]

Some brutal cold flooding southwards into Eastern Europe at T72 on the UKMO.

 

 

[MR EXTREMES]

to be fair the gfs does have another go at under cutting and gfs always had issues with scandi heights under doing its strength.

but this chart showing a stormy outlook does show that its hung around and made inroads into the uk but certainly more southerly tracked than so far this winter.

[Mucka]

9 minutes ago, inghams85 said:

Just to add to Chiono's post.......

You have just posted some ensembles as evidence of what an undercut looks like and try aren't undercuts AT ALL!

The UKMO almost couldn't be more classical undercut if it tried!

 

You have parroted something you know nothing about.

 

Oh look here is p9 that I describe as true undercut.

 

 

Now that is amazing given all the energy is going the wrong way according to you and obviously a total fluke I could predicted it before it happen.

 

Here si the jet profile 144 for that run

 

Which way is the jet heading Einstein?

I will draw the jet with big fat crayon for UKMO since we don't have the charts if you like but what you would see is a split jet with a slither of energy heading SE and a lot of energy heading N.

 

I'm done with this now TBH. it is getting like the Twilight Zone.

 

Edited December 27, 2015 by Polar Maritime
To move discussion on..

[chionomaniac]

9 minutes ago, Mucka said:

 

That is a strange post. I respect you Chino but absolutely disagree with what you are saying here.

Are we talking about the 120/144 low and not possibilities for the next low?

If you were right and I wrong then within the ensembles that show what you are describing as undecut (look like UKMO) would go on to show a stronger better oriented block than the ones I describe as undercutting (actually going UNDER the block into Europe and not riding up it toward the pole)

without even looking I can guarantee on the whole that those that have more energy heading SE UNDER the block will have a better oriented.stronger block and cold uppers closer or over the UK than those that send most energy N a la UKMO by 168 and out to end of hi res.

I can only imagine there is some misunderstanding because what I am describing is a a basic reality.

 

I haven't seen the 850's either but I don't need to understand the dynamic at play. 

Not strange but perhaps there is a bit of misunderstanding - regarding the highlighted GEFS ensembles - but none of them show an initial undercut as good as the UKMO at T+144 and I was only replying to your post that said the UKMO wasn't an undercut. The fact is that the GFS op undercuts the block perfectly as well by T+180 - it is just that it has drifted into an unfavourable position for the UK to be affected.

[nick sussex]

Whose watching the ECM from behind the sofa! lol

Apparently Amazons sales have some good offers on sledges! Lets hope the ECM can deliver because its been a dire winter so far for cold.

Amazing to think that within a week if the trough disruption is favourable snow could finally be falling in the UK.

[swilliam]

For me whether we get anything interesting ( from a cold perspective) depends on how far west the block is (i.e. out over and West of Norway). This has two benefits; it stops the cold pool lifting out northwards (round the end of the block) before it gets to us and it means the small lows to the south will head SE and not NE or N. A couple of examples where the block has spread or extended 

You can see from the ens spread this is where the uncertainty is