Model Output Discussion - 8th December Onwards

[BLAST FROM THE PAST]

I'm not suggesting this is a realistic chart in terms of exact synoptics, but isn't this sort of set up what GP suggested before? (wrt heights building near Greenland, and the PV moving east)

And no, I refuse to get sucked in to talking about another easterly (yet)!

No its supposed to be 3c maybe 4c below for parts of Europe and 1-2c below for UK? We are heading away from that anomaly and if the current charts are correct it'll take a monumental cold spell to bring us back into line.

Yes was he previous thread that bad????

BFTP

Edited December 8, 2012 by BLAST FROM THE PAST

[Stoxs]

Latest NAE suggests the chance of some snow showers into the ne late Monday possibly into East Anglia and also east Kent later, the flows quite slack so unlikely to make much progress inland.

In terms of the GFS we can only hope thats its overdoing that shortwave as really that looks bad news in terms of rain and wind.

In terms of the overall pattern all the models agree on the Atlantic making progress, but really how far east is uncertain and also what impact high pressure will have to the east.

Hi Nick

Now i am not going hunting for it but i am sure you posted a very simliar quote last thursday/wednesday have we really been on the polar express that long and now ended up back where qwe started?

My opinion is this set up is changing all the time and slowly heading down the cold tunnel again, i can see this warmer trend that was progged for the next 2/3 weeks by some erode andc ould end up a few days at best if not less.

need to wait and see.

[Frostbite80]

It's where a low pressure system slides under high pressure to the south of the uk and pulls in cold air from the east, it can produce a good dumping of snow if conditions are right. :-)

[snowblues]

If the atlantic is to drop down a gear heading in to the uk in the upcoming outputs,could the forcasts for the next say 72hrs change again.!I dont mean raging easterly,just more of a easterly wind direction.

Edited December 8, 2012 by snowblues

[Buriedundersnow]

definate step up compared to the 12z.

is there any chance with a few more upgrades things could be brought forward a little more and if we do see upgrades has it just been the case of the models having something they had trouble working through.

[Gavin Hannah]

If the atlantic is to drop down a gear heading in to the uk in the upcoming outputs,could the forcasts for the next say 72hrs change again.I dont mean raging easterly,just more of a easterly wind direction.

theoretically, it could go a completely different direction from now but is very unlikely. 72 hours is pretty close. I certainly haven't seen any major divergence that close to t.0..

[legritter]

Taking all of todays info and charts into consideration an extremely very interesting and frustrating pre christmas real mix looks likely ,with plenty of nail biting days and pram shaking and the prozack bottle and razors coming out .to me it looks like there is a signall for an eventual path of lows tracking to our south .and going by pressure finland russia there is going to be a big build of frigid air .most world northern hemisphere forums etc also talk of polar vor on the move ,which on modells we are seeing .stay focussed gang and dont forget with the HIGHS comes the LOWS [moods i meen ] cheers

[Paul White.]

Hi I 99% sure that an undercut is an area of low pressure moving east underneath a block of high pressure moving west. This would result in easterly winds remember wind direction around a high pressure is clockwise and anticlockwise around the low pressure I hope his helps nd if I am wrong I will be put right by one of the brilliant members in here.

Paul

Edited December 8, 2012 by paulwhite22

[Ian Brown]

That low just doesn't look 'natural' to me, don't ask me why, but to me a good indication that the atlantic incursion just isn't modelled anywhere near right, both in terms of angle and speed. My (limited) experience suggests that the latter part of next week is nowhere near understood from any of the big models.

I think the 18z has 'thrown one in' here, with this bizarre deepening feature that is separate from the rest of the jet. One for the bin I think.

[nick sussex]

Hi Nick

Now i am not going hunting for it but i am sure you posted a very simliar quote last thursday/wednesday have we really been on the polar express that long and now ended up back where qwe started?

My opinion is this set up is changing all the time and slowly heading down the cold tunnel again, i can see this warmer trend that was progged for the next 2/3 weeks by some erode andc ould end up a few days at best if not less.

need to wait and see.

Given recent events its hard to say what will pop up. However the Atlantic is going to make a return and this isn't great news for those who have had enough of the rain and all the problems.

In terms of a colder pattern well for cold lovers the quickest route is the Atlantic making less eastwards progress , ejecting a shortwave east or se into France which for good reason all round we want to be much weaker and the energy being deflated away from the main trough to the west.

If the high stays far enough north then a chance then to develop a colder flow but really I think we have to wait for the models to see whether they're going to retrogress the pattern.

Given the recent easterly fiasco I think its best for people to have low expectations, especially as we're likely be dealing with yet more possible shortwave drama!

[Nick L]

An undercut in the simplest terms is when a low pressure goes underneath a high pressure or a "block". The result can mean the UK being on the northern side of the low where the coldest temperatures are, and potentially some snowfall!

Edited December 8, 2012 by Nick L

[Zenarcher]

What's and undercut?????

Someone may give you a better explanation,

I've drawn out a chart below,

It's when energy like a low pressure system goes under a high or block this then can help move it into a better position like more West to Greenland.

[Stoxs]

Given recent events its hard to say what will pop up. However the Atlantic is going to make a return and this isn't great news for those who have had enough of the rain and all the problems.

In terms of a colder pattern well for cold lovers the quickest route is the Atlantic making less eastwards progress , ejecting a shortwave east or se into France which for good reason all round we want to be much weaker and the energy being deflated away from the main trough to the west.

If the high stays far enough north then a chance then to develop a colder flow but really I think we have to wait for the models to see whether they're going to retrogress the pattern.

Given the recent easterly fiasco I think its best for people to have low expectations, especially as we're likely be dealing with yet more possible shortwave drama!

As Ian and others have pointed out these latest charts look and act unreal, where we end up who knows.

I am just glad i aint getting paid to stand up in front of a camera and tell all what its going to be like by the end of the week!

I have been here to long to belive much that the models throw out, i did get suckered into the latest one because it looked to good for cold/snow and expected it to be half what it showed not event hought it could be the total opposit! amazing

certain there will be a few surprises in store in the following week.

[Just Before Dawn]

GFS is notorious for throwing insane low pressure features around the place outside the reliable (which is about 15 minutes at the moment!!!) but the dartboard low that shuffles along the channel at T+177-ish is out of the top drawer. No doubt it'll be gone on the 00z runs, and even if it's there, I'd expect to see it hugely moderated. At least lets hope so, because as it stands at the minute, it would be driving water in front of it past The Bay of Biscay into the Channel, then pushing it onto shore on the back of hurricane-force winds for 8-12 hours. Then as it moves east, it pulls 60mph+ winds onto the north coast of Devon and Somerset as well as putting down a lot of precipitation exactly where we could do with an extended dry period. Major flooding again for the SW, and potentially a significant coastal flooding risk as far east as East Sussex and western parts of Kent.

Still, as I said, hopefully it will have disappeared on the next run.

[Catacol]

I think what the 18z GFS shows (though bear in mind that historically it is not the best of runs...) is that the medium range output is not going to the shredder. I did suggest in answer to one post earlier today that low pressures zipping from SW to NE was never on the cards unless the output was totally upside down. Tonight we see the block holding a bit stronger... as some have pointed out over and over again might be the case. Remember anomaly guidance still has higher than average pressure to the north and lower than average to the south. That is, by any other description, a "block" ie a pressure pattern providing resistance to the usual flow of west to east.

What has disappeared is any obvious chance of a very cold easterly in the short term, but the mild/cold battle for the end of this week that has replaced it is no less interesting. As was said yesterday there is still a good chance that somewhere in the UK will receive a pasting from this, though it is very hard to know where.

The moral of the story is not to take op output on a particular day as gospel. Temperatures are going to stay below normal whether it be from NE or NW winds, and with the vortex wobbling around so catastrophically I suspect there is a great deal of potential for variable output for the foreseeable future. I repeat, as I have done at least twice in the last few days, that we need a bit of luck from here. The hemispheric pattern has put a stop to any sustained "zonal" westerly regime because the vortex is incoherent and, if GP is correct, liable to shatter in the next 3 weeks or so. What we are left with is fragments of energy breaking off here and there, and high pressure building at high latitude in areas where the vortex is weak. As a few have pointed out today the vortex is forecast to wobble over to Siberia: that should actually increase the retrogression signal of the heights currently to our north east and as these heights transfer the idea of a northerly dropping in over Scandy is quite sensible. However there are lots of ifs and buts to this... and no clear forecast is going to be possible at range. However one forecast that will NOT be accurate will be for weeks of atlantic driven weather. There simply isnt the structure over the pole to produce it.

For the coming week we have been (it would appear) unlucky in that the vortex fragment left behind over Canada as wobble takes place has brought more energy with it than we want, and provided more impetus than coldies want. However it will be temporary. So our pattern is still exciting... it is still open to short range changes according to the behaviour of the broken vortex - a situation which I suspect the models will not handle at all well - and I honestly think we will be unlucky if we dont see at least a few days of something special in terms of cold out of this in the next 2 - 3 weeks.

Patience grasshopper.

Edited December 8, 2012 by Catacol_Highlander

[Ian Brown]

What's and undercut?????

If you want to look at the best example of undercutting lows, giving a lot of snowfall particularly to Southern Britain, run the archive charts on wetterzentrale from the end of Jan 1947 to around the 10th Of Feb.

[Hodgheg]

Here are my thoughts. I think this short lived cold may have a few short term surprises, i dont think the models are going to be reliable past say 120z. I think after say a week atlantic influence, the block will try to bring more of an influence again.

[nick sussex]

as have i and tried to point out why but no-one seems to have noticed!!

Generally I follow a rule with renewed Atlantic signals where you have blocking to the east.

Its best to wait for the models to settle down and see whether they've been too progressive, the first ECM run placed things further east, the next has made some westwards correction with also a more nw/se tilt. Will this continue is the question I suspect most cold lovers will be wondering.

I think we need to see a few more runs to see what the general consensus might be, also the placement of the Russian high is crucial, the further north and west remains the better chances for cold.

I should add its quite high risk with high pressure to the east if this slips too far south with energy running over top as this can just force a stalemate.

So whatever happens if the high is going to tease us it has to stay north extending a ridge nw towards Scandi.

Edited December 8, 2012 by nick sussex

[Bristawl Si]

I think i'd place more confidence in a last minute backtrack to something more interesting (colder/snowier) for many in the UK from late next week if the easterly and deep cold was already present.

If there is to be more of a battleground event then my recollection from past events is that the cold needs to have been on these shores for a few days before the onslaught of any atlantic systems.

[Weather Boy]

I think the 18z has 'thrown one in' here, with this bizarre deepening feature that is separate from the rest of the jet. One for the bin I think.

Yes, who, apart from total newbies to model watching, would seriously think that we are going to get an Atlantic low at anything like 955 mb at this time of year, especially given that it is the GFS which is notorious for over-blowing lows at this range. I would merriy stake my mortgage at 2-1 on us not seeing a low that goes below 960 and bet you at evens on a pressure level quite a lot higher than that - it's just not going to happen.

That poses a question for people more knowledgable than me. If the GFS (admittedly only one run) is sending a hypothetical low with so much energy under the block, given that we know that the low will be weaker than that, does it not follow that an undercut is actually more likely than the models are currently giving us, throwing up a scenario of a channel low giving very heavy snow to S Britain. ie - if we have a low at (guess) 985-990 mb, with less energy than the ludicrous low currently being shown, is that not more likely to be deflected by the low than currently shown?

Or is this just wishful thinking on my part.

[Froze were the Days]

Never seen such continuous messy runs particularly from the GFS, there are so many small LP's and HP's at strange latitudes with the JET all over the place not just on this 18z but over recent weeks it's anything but the 'default' zonal or meridianal pattern we have been accustomed to over numerous winters (before 2008) - no wonder it's been such a pain in the backside forecasting of recent times.

If I was to make a forecast for the rest of the month based on the output we have seen and going to experience I don't think it would be anywhere near zonal and your mild mush but transient less cold spells with always the possibility of returning cold conditions which never last long as the synoptics look so disturbed. Strange days ahead and expect even more 'ups and downs'.

[gaia rules]

Generally I follow a rule with renewed Atlantic signals where you have blocking to the east.

Its best to wait for the models to settle down and see whether they've been too progressive, the first ECM run placed things further east, the next has made some westwards correction with also a more nw/se tilt. Will this continue is the question I suspect most cold lovers will be wondering.

I think we need to see a few more runs to see what the general consensus might be, also the placement of the Russian high is crucial, the further north and west remains the better chances for cold.

OK my first post although been chart watching for 35 years and did work at Met Office. The Atlantic low seems to be disrupted in this later run with a weaker jet leading to the weird FI channel low and the heights are again falling from the north. With that Russian High and cold pool in the east moving closer again there is the hint of attempt number 2 of an easterly mid next week (10 days) . Although as everyone has said about this situation we really cant see beyond 120hrs and it takes at least 3 attempts for an easterly to arrive!

Edited December 9, 2012 by gaia rules

[Panayiotis]

Welcome to Netweather,glad we have another ex-professional joining the discussion!

[nick sussex]

OK my first post although been chart watching for 35 years and did work at Met Office. The Atlantic low seems to be disrupted in this later run with a weaker jet leading to the weird FI channel low and the heights are again falling from the north. With that Russian High and cold pool in the east moving closer again there is the hint of attempt number 2 of an easterly mid next week (10 days) . Although as everyone has said about this situation we really cant see beyond 120hrs and it takes at least 3 attempts for an easterly to arrive!

Welcome to net weather. Yes we're back to easterly teases, sometimes I wish a Greenland high would appear they're far less trouble although of course easterlies have a certain allure!

The GFS low because its deeper the ne momentum makes the undercut more difficult, also theres still far too much energy in that troughing to the west.

I think alot depends on retrogression and how much residual energy is left over to the west after the main PV has moved to Siberia, I doubt the models have the right solution on that yet.

[Nick123]

Ive been following this topic and the previous discussions since the "beast from the east" was first thrown into the mix, my initial reaction was I was totally taken in, but then a few days after the general concensus seemed to be that it was "game over." However, I have always believed that there would be a chance of it returning, or atleast something simimar based on the fact that the charts went from an extreme cold outlook to a very mild outlook within a matter of days. I agree totally with the last few posts, looks very interesting!